Chapter 1: Key Information

The ear is a complex organ that enables orientation in space, everyday physical activities and social communication. While the anatomy of the ear may be intimidating to some extent, we have tried to provide a simplified but explanatory picture to enhance your comprehension of processes important for diving.

Pressure equalization in the middle ear is the most important skill for divers. If not mastered properly, divers can get injured and sometimes permanently disabled. In divers with healthy ears, ear barotrauma is preventable. Divers should invest time and effort to master equalization techniques.

In this chapter, you’ll learn about:

Anatomy of the Ear

The ear is the organ of hearing and balance. It consists of a cavity in the skull structure lined with soft tissue, which encloses three distinctive spaces filled with air or liquid (external, middle and inner ear); these distinctive spaces host both sound transmission mechanisms and sensory apparatuses.


The external ear includes the pinna (auricle) and the ear canal up to the eardrum (tympanic membrane), which separates it from the middle ear. The lining of the external ear is skin rich with glands that produce earwax.

The middle ear is a cavity in a temporal bone lined with a thin layer of tissue similar to that found in the nose and throat. It is separated from the ear canal by the eardrum and connected to the throat via the Eustachian tube. It includes three tiny bones (auditory ossicles) forming the chain attached to the eardrum on one side and to the oval window membrane on the inner-ear side. The middle-ear space is filled with air at ambient pressure, which needs to be equalized when ambient pressure changes (as occurs in diving or flying). This is accomplished by moving air in or out through the Eustachian tubes, which connect the throat to the middle ear, using equalization techniques such as the Valsalva maneuver.

The inner ear, or labyrinth, includes the cochlea (hearing organ) and the vestibule and semicircular canals (balance organs). The cochlea and the vestibule are the origin of the auditory and vestibular nerves.


Pressure waves transmitted by air or water are funneled by the pinna and the ear canal to the tympanic membrane. The pressure waves cause the tympanic membrane to vibrate, which causes the auditory ossicles to move simultaneously in response. The stapes (the last bone in the chain) strikes the oval window of the cochlea. Since this is a closed system, when the oval window is pushed inward, the round window pushes outward. The fluid within the cochlea transmits the pressure waves to the auditory nerve, which in turn, sends signals to the brain that are interpreted as sound.

Parts of the vestibule are projections known as the semicircular canals. The fluid within this system moves correspondingly with head movement. Inside the semicircular canals are hairlike structures called cilia. The cilia detect movement of the fluid through the canals and send the signals through the vestibular nerves to the brain, where the movement is interpreted and used to help determine the position of the head in three-dimensional space.

Middle-Ear Equalization

Middle-ear equalization is a basic, required diver skill that enables the equalization of the pressure in the sinuses and middle-ear spaces with ambient pressure.

Procedure in Practice

As divers descend in the column of water, environmental pressure increases in a linear fashion at a rate of one-half pound per square inch (PSI) for each foot (0.1 kg/cm2 for each meter) and transmits across the body tissues and fluids. Boyle’s law describes how the volume of the gas decreases when pressure increases, if the amount (mass) of gas and the temperature remain the same. The middle ear is a rigid cavity with the exception of the eardrum. So when pressure increases, the only way for the volume to decrease is the bowing of the eardrum toward the middle-ear cavity (unless gas is added to the space). After the eardrum stretches to its limits, further reduction of middle-ear cavity volume is not possible; if descent continues, the pressure in the middle-ear cavity remains lower than its surroundings. Modest pressure difference will cause leakage of fluid and bleeding from the eardrum and mucosa lining the middle-ear cavity (ear barotrauma O’Neil grade 1). When the pressure difference reaches 5 PSI (0.35 bar), the eardrum may rupture in some divers; at a pressure difference greater than 10 PSI (0.75 bar), rupture will occur in most divers (ear barotrauma O’Neil grade 2). In addition, sudden and large pressure changes may cause inner-ear injury.

So now you understand why during descent you must let more gas into your middle ear to keep the volume of the gas constant and equalize the pressure. A normal middle ear has only one physical communication with the source of additional gas, and that is the Eustachian tube that connects to the nasal cavity (rhinopharynx). Under normal circumstances, the Eustachian tubes are closed, but every time we swallow or yawn, the muscles in our throat allow for a small transient opening that is enough to ventilate our middle ear and compensate pressure.

Nothing challenges our ears and Eustachian tubes more than scuba and breath-hold diving. To become a safe scuba diver and avoid middle-ear injuries, it is essential that you understand the effects of Boyle’s law and learn how to actively let air into your middle ears via the Eustachian tubes. In the following sections, you will find different equalization techniques for you to try.

On ascent, the surrounding pressure decreases and the pressure in the middle remains higher if the gas has no way to leave the middle-ear cavity. When the pressure in the middle ear exceeds surrounding pressure by 15-80 centimeters of water (cm H2O) which corresponds to an ascent in water of 0.5-2.5 feet, the Eustachian tubes open, and surplus gas escapes. If your ears do not equalize at the same rate and the pressure difference reaches about 66 cm H2O (2 feet), vertigo due to unequal pressure stimulus (alternobaric vertigo) may occur.

Upper respiratory tract infections, hay fever, allergies, snorting drugs, cigarette smoking or a deviated nasal septum may compromise equalization. When properly employed, the following techniques are effective in middle-ear and sinus squeeze in healthy subjects.

Equalization Techniques

Passive: Requires no effort. Occurs during ascent.

Voluntary tubal opening: Try yawning or wiggling your jaw. Up to 30 percent of divers can successfully master this technique.

Valsalva maneuver: Pinch your nostrils, and gently blow through your nose.

Toynbee maneuver: Pinch your nostrils and swallow (good technique if equalization is needed during ascent).

Frenzel maneuver: Pinch your nostrils while contracting your throat muscles, and make the sound of the letter “k.”

Lowry technique: Pinch your nostrils, and gently try to blow air out of your nose while swallowing (think Valsalva maneuver meets the Toynbee maneuver).

Edmonds technique: Push your jaw forward, and employ the Valsalva maneuver or the Frenzel maneuver.

The Toynbee maneuver is an effective technique for equalizing your ears during ascent

Tips for Equalization

  1. Prior to descent, while you are neutrally buoyant with no air in your buoyancy control device (BCD), gently inflate your ears with one of the listed techniques. This gives you a little extra air in the middle ear and sinuses as you descend.
  2. Descend feet first, if possible. This allows air to travel upward into the Eustachian tube and middle ear, a more natural direction. Use a descent line or the anchor line to control the speed of descent.
  3. Inflate your ears gently every few feet for the first 10 to 15 feet.
  4. Pain is not acceptable. If there is pain, you have descended without adequately equalizing. Ascend a few feet until the pain stops.
  5. If you do not feel your ears opening, stop and try again; you may need to ascend a few feet to diminish the pressure around you. Do not bounce up and down.
  6. It may be helpful to tilt the blocked ear toward the surface.
  7. If you are unable to equalize, abort the dive. The consequences of descending without equalizing could ruin an entire dive trip or cause permanent damage and hearing loss.
  8. Decongestants and nasal sprays may be used prior to diving to reduce swelling in the nasal and ear passages. If your doctor agrees with your decision to use decongestants, take them one to two hours before descent. They should last from eight to 12 hours, so you don’t need to take a second dose before a repetitive dive. Nasal sprays should be used approximately 30 minutes before descent and usually last 12 hours. Take caution when using over-the-counter nasal sprays; repeated use can cause a rebound reaction resulting in increased congestion and possible reverse block on ascent. Decongestants may have side effects. Do not use them before dive if you do not have previous experience.
  9. If at any time during the dive you feel pain, experience vertigo or note sudden hearing loss, abort the dive. If these symptoms persist, do not dive again and consult your physician.

Next: Chapter 2 – Injuries >

Chapter 2: Injuries


Ear injuries are the leading cause of morbidity among scuba divers. The most common injury is middle-ear barotrauma (MEBT). Most cases of MEBT are mild, heal spontaneously and are never reported. In more serious cases, divers seek medical attention, and some call DAN. Various surveys indicate that more than 50 percent of all divers experience MEBT at least once. In contrast, only 4.4 percent of divers experience DCS in their lifetime.

Divers are affected by various other ear injuries, many of which are preventable, detailed in the chapter that follows.

In this chapter, you’ll learn about:

Middle-Ear Barotrauma (MEBT)

Middle-ear barotrauma is the accumulation of fluid and blood in the middle ear or rupture of the eardrum as a consequence of failed equalization of pressure in the air space of the middle ear during diving or flying.


The air pressure in the tympanic cavity­ — air-filled space in the middle ear — must be equalized with the pressure of the surrounding environment. The Eustachian tube connects the throat with the tympanic cavity and provides passage for gas when pressure equalization is needed. This equalization normally occurs with little or no effort. Various maneuvers, such as swallowing or yawning, can facilitate the process.

An obstruction in the Eustachian tube can lead to an inability to achieve equalization particularly during a descent when the pressure changes fast. If the pressure in the tympanic cavity is lower than the pressure of the surrounding tissue, this imbalance results in a relative vacuum in the middle ear space. It causes tissue to swell, the eardrum to bulge inward, leakage of fluid and bleeding of ruptured vessels. At a certain point an active attempt to equalize will be futile, and a forceful Valsalva maneuver may actually injure the inner ear. Eventually, the eardrum may rupture; this is likely to bring relief from the pain associated with MEBT, but it is an outcome to be avoided if possible.

Factors that can contribute to the development of MEBT include the common cold, allergies or inflammation — conditions that can cause swelling and may block the Eustachian tubes. Poor equalization techniques or too rapid descent may also contribute to development of MEBT.


Divers who cannot equalize middle-ear pressure during descent will first feel discomfort in their ears (clogged ears, stuffed ears) that may progress to severe pain. Further descent only intensifies the ear pain, which is soon followed by serous fluid buildup and bleeding in the middle ear. With further descent, the eardrum may rupture, providing pain relief; this rupture may cause vertigo, hearing loss and exposure to infection.


While diving: When feeling ear discomfort during descent, you should stop descending and attempt equalization. If needed, ascend a few feet to enable equalization. If equalization cannot be achieved, you should safely end the dive.

First aid: When feeling fullness in one’s ears after diving, abstain from further diving. Use a nasal decongestant spray or drops. This will reduce the swelling of nasal mucosa and Eustachian tube mucosa, which may help to open the Eustachian tube and drain the fluid from the middle ear. Do not put any drops in your ear.

Treatment: Seek a physician evaluation if fluid or blood discharge from the ear canal is present or if ear pain and fullness lasts more than a few hours. If vertigo and dizziness are present, which may be a symptom of inner-ear barotrauma, you should seek an urgent evaluation. Severe vertigo and nausea after diving require emergency medical care.

Fitness to Dive

Return to diving may be considered if a physician determines that the injury is healed and the Eustachian tube is functional.


  • Do not dive with congestion or cold.
  • Descend slowly. If unable to equalize after a few attempts, safely end the dive to avoid significant injury that may prevent you from diving the rest of the week.

Tympanic Membrane Rupture (Perforated Eardrum)

Tympanic membrane perforation is a tear of the eardrum, which can occur while scuba diving due to failed middle-ear pressure equalization.


The tympanic membrane (TM) is a tissue separating the external ear from the middle-ear space. It is attached to a chain of small bones (auditory ossicles) located in the middle ear. The TM also serves as a barrier between the sterile middle-ear space and the ambient environment.

Eardrum rupture may be caused by descending without equalizing the pressure in the middle ear, by a forceful Valsalva maneuver, explosion, a blow to the ear/head, or acoustic trauma. It is usually accompanied with pain; rupture relieves the pressure (and pain) in the middle ear and may be followed by vertigo. There may be some bleeding in the ear canal.

Contributing factors include congestion, inadequate training and excessive descent rates.


  • Ear pain during descent that stops suddenly
  • Clear or bloody drainage from ear
  • Hearing loss
  • Ringing in the ear (tinnitus)
  • Spinning sensation (vertigo)
  • Nausea or vomiting that can result from vertigo


Most perforated eardrums will heal spontaneously within a few weeks. It may be necessary to treat nasal and sinus congestion. If the tear or hole in your eardrum does not heal by itself, treatment will involve procedures to close the perforation. These may include:

  • Eardrum patch: An ENT specialist may seal the tear or hole with a paper patch. This is an office procedure in which an ENT applies a chemical to the edges of the tear to stimulate growth and then applies a paper patch over the hole to provide a support structure for the growth of eardrum tissue.
  • Surgery: Large eardrum defects may be fixed by surgery (tympanoplasty). An ENT surgeon takes a tiny patch of your own tissue and plants it over the hole in the eardrum. This procedure is done on an outpatient basis, meaning you can usually go home the same day unless medical conditions require a longer hospital stay.

For an ENT referral in your area, email  or call the DAN Medical Information Line at +1 (919) 684-2948.

Fitness to Dive

If your physician feels the healing is solid and there is no evidence of Eustachian tube problems, you can return to diving within several months. Chronic perforations that do not heal are a contraindication to diving.


Do not dive with congestion. Maintain a comfortable rate of descent, and equalize as needed.

O’Neill Grading System

The O’Neill grading system is a new way to grade the severity of middle-ear barotrauma. It is simplified and is expected to provide more consistent diagnosis with sufficient details to direct the treatment.

Grade 0
Eustachian Tube Dysfunction

  • Baseline photo depicting anatomical appearance of the TM before exposure to pressure
  • Symptoms with no anatomical change (no trauma) from baseline

Grade 1

  • Erythema increased from baseline
  • Fluid or air trapping (visible bubble) in the middle-ear space

Grade 2

  • Any bleeding noted within the tympanic membrane or middle-ear space
  • Perforation

Inner-Ear Barotrauma

Inner-ear barotrauma is damage to the inner ear due to pressure differences caused by incomplete or forceful equalization. A leak of inner-ear fluid may or may not occur.


Mechanisms of injury

The inner ear is separated from the external world by the middle ear. It is the organ for hearing and balance. When the pressure in the middle-ear space is properly equalized, the risk of inner-ear barotrauma is extremely low.

If the pressure in the middle ear is not equalized during descent, the water pressure on the eardrum transfers inward through the middle-ear ossicles to the oval windows, and the round window bulges outward. The pressure itself may damage sensitive inner-ear structures. If the pressure is excessive, either the oval window or, more commonly, the round window may tear, and the inner-ear fluid (perilymph) may leak into the middle ear (perilymph fistula).

The Valsalva maneuver increases the pressures in cranial tissues and circulation, which may transmit to the cochlear fluid, causing an outward movement of the round window. Pressure waves alone can cause damage to the inner ear without window rupture. If the rupture occurs, the loss of fluid from inner ear leads to damage of the hearing organ and sometimes of the balance organ. If the leak is not stopped soon by spontaneous healing or surgical repair, permanent hearing loss may occur.


Divers may experience:

  • Severe vertigo
  • Hearing loss
  • Ears roaring/ringing (tinnitus)
  • Involuntary eye movement (nystagmus)
  • Fullness of the affected ear

Symptoms of middle-ear barotrauma are almost always present. Vertigo is usually severe and accompanied by nausea and vomiting. Hearing loss can be complete, instant and permanent, but divers usually lose just the higher frequencies. The loss becomes noticeable only after a few hours. You may not be aware of the loss until you have a hearing test.


In case of vertigo underwater, abort the dive, and obtain assistance to reach the surface safely. Begin surface oxygen if decompression illness is suspected. First aid providers should conduct a complete neurological exam and note any deficits.

Inner-Ear Barotrauma or Inner-Ear Decompression Sickness?

It is important to distinguish between these two conditons, because their treatments differ. The standard treatment for DCS of any kind is hyperbaric oxygen treatment in a recompression chamber; recompression or any pressure change is contraindicated when inner-ear barotrauma is likely. While the symptoms are similar in both conditions, barotrauma is preceded by failed equalization of middle-ear pressure and usually occurs at the beginning of dive, while DCS occurs due to failed decompression at the end of the dive.

Definitive Treatment

Urgently seek an evaluation by a physician to rule out DCS. If your physician determines it is not DCS, consult an ENT specialist with experience treating divers. For a referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.

Avoid any exertion, middle-ear equalization, altitude or diving exposure, sneezing or nose blowing. Do not take aspirin, nicotinic acid (vitamins), other vasodilators or anticoagulants. Conservative treatment includes bed rest in a sitting position and avoiding any strains that can increase intracranial or middle-ear pressure. If symptoms do not improve, surgery may be necessary. Healing of the tear (fistula) usually occurs within a week or two. Hearing loss may become permanent.

Fitness to Dive

Evaluation of fitness to dive requires an expert diving physician and depends on the degree of permanent damage as well as the probability of repeated injury.


In many cases, complete healing occurs spontaneously. If fistula presents and does not heal soon spontaneously, surgery may be recommended. In some cases, the inner ear may be damaged permanently; the body may adapt to one side not working properly. If injury occurs to the other ear, the situation can be serious and may involve incapacitating balance problems.


Learn gentle but effective equalization techniques, and avoid aggressive employment of the Valsalva maneuver. Do not dive when congested.

Perilymph Fistula

A perilymph fistula is a tear in the round- and/or oval-window membranes through which inner-ear fluid (perilymph) is leaking.



Leakage of perilymph from the labyrinth may occur when the round or oval window is disrupted due to severe middle-ear barotrauma or forceful Valsalva maneuver.


The symptoms of perilymph fistula may include dizziness, vertigo, imbalance, nausea and vomiting. Some people experience ringing (tinnitus) and fullness in the ears, and many notice some hearing loss. Symptoms worsen with changes in altitude (elevators, airplanes or travel over mountains), weather changes and with physical exertion.


This condition can usually be managed conservatively with absolute bed rest in the sitting position. Straining, sneezing, nose blowing, sexual activity, loud noises and middle-ear equalizing should be avoided to prevent pressure waves in the inner ear.

The round-window fistula often heals spontaneously within a week or two with this regimen, but if hearing loss progresses or the other features persist, it may be necessary to resort to surgery to repair the round-window leak.

Fitness to Dive

Even after the acute symptoms of an oval- or round-window fistula have resolved, the diver’s future in diving is questionable. Flying should be completely avoided for several months to allow complete healing of the injury or the surgical repair.

For a referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.


Ensure the Eustachian tubes are functioning properly before diving by gently equalizing on the surface.

Alternobaric Vertigo

Alternobaric vertigo occurs during descent, ascent or immediately after surfacing from a dive and is caused by unequal pressure stimulation in each ear.


According to various sources, up to 25 percent of divers experience alternobaric vertigo at some time.


During ascent, air in the middle-ear space expands, relative pressure increases, the Eustachian tubes open passively, and gas escapes through the Eustachian tubes into the nasopharynx. Occasionally the Eustachian tube may obstruct this flow of air, with subsequent air distension and increased pressure sensation in the middle-ear cavity during ascent. If the obstruction is one-sided and the pressure difference is greater than 60 centimeters of water, vertigo may occur as the pressure increase stimulates the vestibular apparatus. Usually it is relieved by further ascent, because the increasing differential pressure in the middle-ear space forces open the Eustachian tube and vents the excess air. Contributing factors include middle-ear barotrauma during descent, allergies, upper respiratory infections (congestion) and smoking.


The symptoms of alternobaric vertigo may include disorientation, nausea and vomiting.

Note: The disorienting effects of vertigo while diving are extremely dangerous. The inability to discern up from down, follow safe ascent procedures, and the risks associated with vomiting pose a significant hazard to the diver as well as other divers in the water.


Advice provided by Dr. Carl Edmonds about how to manage alternobaric vertigo during a dive:

“If a diver encounters ear pain or vertigo during ascent, he should descend a little to minimize the pressure imbalance and attempt to open the Eustachian tube by holding the nose and swallowing (Toynbee or other equalization maneuver). If successful, this equalizes the middle ear by opening it up to the throat and relieves the distension in the affected middle ear.

“Occluding the external ear by pressing in the tragus (the small fold of cartilage in front of the ear canal) and suddenly pressing the enclosed water inward may occasionally force open the Eustachian tube. If this fails, then try any of the other techniques of equalization described previously, and attempt a slow ascent.”

Uncomplicated cases resolve quickly within minutes upon surfacing. If symptoms persist, see your primary care physician or an ENT specialist. Do not dive if you have equalization problems.

Associated injuries include middle-ear barotrauma and inner-ear barotrauma; alternobaric vertigo may occur during descent or ascent, but is commonly associated with a middle-ear barotrauma of ascent (reverse squeeze). Other conditions such as inner-ear DCS or caloric vertigo (when cold water suddenly enters one ear) should be ruled out.

Fitness to Dive

As soon as all symptoms and contributing factors have been resolved, a diver may return to diving.


Take measures for the prevention of ear barotraumas. Avoid the unequal pressurization of the ear by avoiding tight-fitting wetsuit hoods or earplugs. Maintain good aural hygiene. Do not dive when congested or unable to equalize.

Reverse Squeeze

A reverse squeeze is barotrauma due to an inability to release pressure from the middle ear on ascent.


Pressure must be released from the middle ear as the diver ascends, or the expanding air will bulge and even rupture the eardrum. Expanding air normally escapes down the Eustachian tubes, but if the tubes are blocked with mucus at depth (usually the result of poor equalization on descent, diving while congested or relying on decongestants that wear off at depth), barotrauma can result.



  • Pressure, fullness in ear
  • Ear pain
  • Vertigo


While diving: Sometimes one of the equalizing techniques used on descent will clear your ears on ascent. Pointing the affected ear toward the bottom may help, too. Ascend as slowly as your air supply allows. Increasing pressure usually opens the Eustachian tube and relieves overpressure. However, in rare cases it may persist all the way up. In that case, you will have to endure the pain to reach the surface. Notify your buddy, and stay in close proximity.

First aid: Nasal decongestant spray may help open the Eustachian tube. A physician evaluation is advised if you experience vertigo, protracted pain and fullness of the ears.

Fitness to Dive

Repeated episodes require an ENT evaluation. For an ENT referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.


Prior to diving, try equalizing on the surface to ensure Eustachian tube function is adequate.

Facial Baroparesis

Facial baroparesis is reversible paralysis of the facial nerve due to increased pressure in the middle ear when ascending in an airplane or from scuba diving.


Mans Bell’s Palsy

The facial nerve is a cranial nerve that controls the muscles of the face. On its way from the muscle to the brain it passes through the channel in the wall of the middle-ear space. Pressure changes in that space normally have little or no effect on the nerve.

In some people, the canal of facial nerve misses the bony wall and is separated from the middle-ear cavity by only a thin membrane. If such a person experiences an overpressure in the middle ear equal or greater to the capillary pressure, circulation to the facial nerve stops, the facial nerve loses its functionality and facial muscle is paralyzed (facial baroparesis). This can happen while flying or diving. Fortunately, the pressure in the middle ear returns to normal soon after the exposure, restoring the circulation to the nerve and enabling its functionality. Facial baroparesis tends to recur with flying or repeated diving.


Symptoms include numbness, paresthesia, weakness or even paralysis of the face. Decreased sensation and a facial droop can be seen, generally on one side of the face.


Facial baroparesis usually is discovered postdive. Even when its duration is brief and it resolves spontaneously, the patient should be evaluated by a physician to exclude other possible causes such as stroke, infection, trauma or decompression sickness.

In rare instances of protracted facial baroparesis, treatment may be necessary. There is experimental evidence that overpressure lasting more than 3.5 hours may cause permanent damage. Divers who continue to experience facial numbness and drooping should see a physician within three hours.

Fitness to Dive

This condition is self-limiting and resolves spontaneously within hours, but it can recur with diving or flying. Return to diving may be considered when symptoms have completely resolved and have been determined to be the result of facial barotrauma.


Learn gentle but effective equalization techniques. Do not dive with congestion.

Temporomandibular Joint Syndrome (TMJ)

Temporamandibular joint syndrome is pain in and around the temporomandibular joint caused by prolonged gripping of a mouthpiece from a snorkel or scuba regulator.



It has been reported that TMJ occurs in 15-20 percent of snorkelers and scuba divers.


TMJ is a chronic inflammation of the jaw joint just in front of the ear. The pain can be great enough to make holding the mouthpiece between the teeth difficult. The condition is exacerbated by local factors such as joint laxity, anatomical factors, capsular or muscular inflammation, or the type of mouthpiece used.

Diving-associated TMJ is thought to result from the forward posturing of the mandible by an ill-fitting mouthpiece and clenching of the mouthpiece, especially with heavy regulators. Diving may aggravate preexisting TMJ. The pain is sometimes severe enough to cause divers to abort the dive. It can occur in novice divers who clench their teeth, sometimes with such intensity that they occasionally bite through the mouthpiece.


  • Pain in the TMJ and ears
  • TMJ clicking or crepitus (cracking or popping sound)
  • Trismus (inability to open mouth fully) and impaired TMJ mobility
  • Dizzy spells (could be hazardous should it occur underwater)
  • Masticatory muscle pain
  • Stuffy sensation in the ears
  • Eustachian tube dysfunction
  • Headache and facial pain


While diving: Work to relax your bite while retaining the mouthpiece in place. If unsuccessful, safely end the dive, surface and consider alternative mouthpiece options.

Definitive treatment: If pain persists, a consultation with a specialist is suggested as solutions are highly individualized. Treatment includes bite adjustment, management of dental problems and the use of orthodontic mouthpieces. Heat and anti-inflammatory drugs are helpful.

Fitness to Dive

Return to diving is possible upon pain resolution. You must also be able to grip the mouthpiece without pain.


Use only a mouthpiece that fits properly. Consider a customized mouthpiece. Correct contributing conditions such as dental problems, anxiety and teeth grinding (bruxism).

Surfer’s Ear

Surfer’s ear is the narrowing of the outer ear canal due to an abnormal growth of bone caused by exposure to cold and wet conditions.



The external ear canal is a tubular structure that conducts sounds and protects the middle ear. Exostosis is a chronic condition characterized by narrowing of the inner half of the ear canal as a result of bone growth. The bony wall grows outward slowly over a period of years in response to local irritation by cold water. These growths are called swimmer’s nodes and are common in swimmers, surfers and divers. This condition is not related to infection nor is it caused by infection; however, the narrowing of the ear canal may prevent water from draining out, which increases susceptibility to outer-ear infections. The bony swellings continue to grow while there is a continued exposure to cold water (such as that found in seawater and outdoor swimming pools in temperate climates). Exostosis often occurs in outdoor enthusiasts in their mid- to late-30s, but individuals who experience significant cold-water exposure — such as surfers, swimmers and divers — can develop the condition earlier.

The narrowed ear canal is more prone to blockage by earwax or debris and more susceptible to swimmer’s ear (otitis externa). An exostosis on the floor of the ear canal can form a sump that retains moisture and is susceptible to infection. Exostosis is seen as a narrowing of the ear canal. The average ear canal is about 0.25 inches wide (7 milimeters). The bone growth may cause it to narrow to 0.04 inches (1 millimeter). Early signs include water trapping in the ear canal after swimming. Debris trapping and infections may make surgery necessary.


External ear infections and difficulty removing water from the external ear canal may be recurrent. Exostosis symptoms in advanced cases include a decreased hearing possibly combined with an increased prevalence of ear infections.

Differential Diagnosis

Other causes of external ear-canal obstruction could include infection or earwax (cerumen) impaction.


In case of decreased hearing or repeated infections, exostosis may be removed surgically.

Fitness to Dive

Exostoses do not affect fitness to dive unless they are occluding the ear canal or causing recurrent infection.


  • Wear a hood in cold water.
  • After diving, rinse both ears with freshwater to flush contaminated water and salt.
  • If prone to ear infections, blow warm air into external canal using a hair dryer (take care to make sure the air is not too hot).
  • If your ears have a natural tendency to build up a blockage of earwax, have them checked regularly, particularly before a prolonged diving trip.

Swimmer’s Ear

Acute inflammation or infection of the outer ear (pinna and ear canal) caused by prolonged exposure to wet and warm conditions is known as swimmer’s ear.



Otitis externa affects one in 200 Americans every year and is present in chronic form in 3-5 percent of the population. Swimmers, surfers and other individuals who are exposed to wet and warm conditions are at an increased risk.


The external auditory canal is the tubular opening between the outside environment and the eardrum (tympanic membrane). It is covered by skin and secretes earwax (cerumen), which helps protect against infection.

Otitis externa, commonly referred to as swimmer’s ear, is the acute inflammation or infection of the external auditory canal, resulting in ear pain and pus discharge.

Breakdown of the external ear canal’s protective barrier leads to infection. Excessive moisture, mechanical trauma or underlying skin conditions are contributing factors. The bacteria normally found in the external ear canal often trigger the infection. With frequent immersion, water swells the cells lining the ear canal. Eventually, these cells separate far enough for the bacteria that are normally found on the surface of the ear canal to penetrate the skin, where they find a warm environment and start to multiply. Otitis externa is more likely to develop if the skin in the ear canal is already chafed and cracked by excessive moisture from showering or scratching. Bacteria or fungus from the water can easily invade damaged skin.

Seborrheic dermatitis, psoriasis and excessive cleaning of wax from the ears that injures the skin lining the external ear canal may increase susceptibility of the ear canal to infection. Excessive debris or cerumen may trap water in the canal.


The chief complaint is generally itching often accompanied by pain, tenderness and swelling of the ear canal. If left untreated, the swelling can increase to include nearby lymph nodes and produce enough pain that moving the jaw becomes uncomfortable.


First Aid

  • Avoid getting in the water until after the problem clears up.
  • Use a hair dryer to carefully dry the ear after you shower (take care to ensure the air is not too hot).
  • In case of pain, over-the-counter pain medications can be effective. Examples of such medications include acetaminophen (Tylenol), ibuprofen (Advil or Motrin) or naproxen (Aleve). Read and follow all instructions on the label.

Stop swimming and diving; schedule an appointment with your physician. Do not put anything in your ear unless instructed to do so. If you have diabetes or take medicine that suppresses your immune system, swimmer’s ear can cause severe problems that require immediate medical attention.

It is important for your physician to rule out external ear squeeze, otitis media and mastoiditis (infection of the bone just behind the ear).

Fitness to Dive

Return to diving is possible once your physician determines that the infection
has resolved.


Keep your ears clean and dry.

  • Dry ears with a towel after swimming or showering by tilting your head and pulling your earlobe in different directions while your ear is facing down.
  • Refrain from putting objects — such as cotton swabs or your finger — in the ear canal or removing ear wax yourself; both actions can damage the skin, potentially increasing the risk of infection.
  • You can dry your ears with a blow dryer if you put it on the lowest setting and hold it at least a foot (about 0.3 meters) away from the ear.
  • Talk to your doctor about whether you should use alcohol-based eardrops after swimming.

If you know you don’t have a punctured eardrum, you can use over-the-counter eardrops or homemade preventive eardrops before and after swimming. This mixture of one part white vinegar to one part rubbing alcohol may help promote drying and prevent the growth of bacteria and fungi that can cause swimmer’s ear. At the end of each day of diving, put five drops of the solution into each ear. Let it stay for five minutes before draining back out.

Next: Chapter 3 – Symptoms >

Chapter 3: Symptoms


Pain is the most common symptom of ear injury, but the most alarming symptoms are vertigo, tinnitus and acute deafness. All three symptoms may be caused by a variety of acute and chronic medical conditions that affect fitness to dive. Acute onset of these symptoms in relation to diving may indicate inner-ear barotrauma or decompression sickness and should prompt medical evaluation.

Vertigo is often confused with dizziness, which has different causes and implications. Divers should be familiar with these symptoms so that they can recognize potential problems and intervene appropriately.

In this chapter, you’ll learn about:

Seasickness or Motion Sickness

Seasickness is a condition individuals may experience when on a moving platform. It involves a general feeling of illness, dizziness, nausea and vomiting. It is also called motion sickness. Passive motions disturb fluid movement within the labyrinth and affects one’s sense of balance and equilibrium. It is exaggerated when the brain receives conflicting messages delivered from the eyes, muscles and joint sensors (proprioceptors). In a closed room, the view indicates that the surroundings are still, while the signals from the labyrinth indicate that the body is moving.

Motion sickness can occur when traveling on a ship, plane, train, bus or car. Some people are more sensitive than others, but if the motion stimuli are strong and the exposure lasts long enough, nearly all individuals will experience it.


The symptoms of motion sickness include dizziness, sweating, nausea, vomiting and a general feeling of discomfort or illness. Symptoms can strike suddenly and progress from simply not feeling well to cold sweats, dizziness and vomiting. Motion sickness is more common in women and in children 2-12 years old. Individuals who suffer from migraine headaches are also more prone to motion sickness. Motion sickness lasts as long as the motion lasts. Once the motion stops, symptoms quickly subside. Some people feel “sea legs” after a long sojourn at sea.


Prevention and Management

If you know you have motion sickness or might be prone to it, consider this advice:

  • On a boat: Stay on deck and focus on the horizon. Avoid inhaling exhaust fumes.
  • In a car: Sit in the front seat. If you are the passenger, look at the scenery in the distance.
  • Do not read in moving vehicles. Reading makes motion sickness worse.
  • Avoid heavy meals prior to diving.
  • Drink plenty of water.
  • Avoid alcohol the evening before you travel.
  • If possible, stand up. Sitting or lying down can make you feel worse.
  • Eat dry crackers to help settle a queasy stomach.
  • Avoid others who have become nauseous with motion sickness.


Motion sickness can be treated with over-the-counter and prescription drug products.

  • Over-the-counter products: Antihistamines are commonly used both to prevent and treat motion sickness. A side effect of antihistamines is drowsiness, which is exaggerated when alcohol is consumed. Drowsiness may adversely affect diver safety.
  • Prescription products: The scopolamine skin patch (Transderm Scop) is a popular option. The patch is applied to the skin area behind the ear at least eight hours before exposure and can help prevent motion sickness for up to three days per patch. Scopolamine may cause dry mouth, blurry vision, drowsiness and dizziness. Patients with glaucoma, enlarged prostate and some other health problems should not use this drug. Be sure to tell your doctor of your existing health problems to help determine which drug is best suited for you.
  • Alternative remedies: Various alternative remedies have been promoted as being helpful in relieving or preventing motion sickness. In most cases, the evidence of efficacy is missing. However, if you have mild symptoms, you may try ginger or peppermint products to ease your symptoms without risking side effects.


Vertigo is the persistent feeling of tilting, swaying, whirling or spinning motion of oneself or of the surrounding world when nothing is moving.


Vertigo during or after diving is a common symptom of middle-ear or inner-ear injury. It is often associated with nausea and in severe cases vomiting. If vertigo happens underwater, the diver may not be able to tell which way is up; panic and vomiting may cause choking and drowning. On land, the patient may not be able to sit or stand

There are various causes of vertigo. In diving, it is most often caused by inner-ear barotrauma. It can also occur from stimulation of one side and not the other, such as when the pressure difference in only one ear equalizes (alternobaric vertigo) or when cold water enters one ear but not the other (caloric vertigo). This type of vertigo disappears as the condition equalizes and leaves no lasting effects except that the associated disorientation, nausea and vomiting while underwater may contribute to diving accidents.

Vertigo is an acute symptom of vestibular injury that may be associated with other symptoms, some of which may become chronic. Symptoms may include imbalance and spatial disorientation, vision disturbance, hearing changes, involuntary eye movement (nystagmus), and cognitive and/or psychological changes, among others.

Differential Diagnosis

Vertigo is not the same as dizziness, lightheadedness or unsteadiness. When you’re dizzy, you may feel lightheaded or lose your balance. If you feel that the room is spinning, you have vertigo.

For vertigo, differentiate between inner-ear decompression sickness (DCS) and inner-ear barotrauma.

General Guidance

  • Vertigo occurring briefly during or after a dive and resolving spontaneously requires evaluation of Eustachian tubes before resuming diving.
  • Persistent vertigo is a sign of serious conditions and requires urgent evaluation by an ENT specialist. For an ENT referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.
  • Severe persistent postdive vertigo is an emergency.

Fitness to Dive

Damage to vestibular organs by DCS, barotrauma or acoustic shock may be permanent. In case of single-ear injury, vertigo may go away in two to six weeks, because the brain learns to compensate and ignores the side that is damaged, but the canal will not heal. The diver will have difficulties maintaining balance in the dark when deprived of visual clues. Damage to both vestibular organs is debilitating and may make certain life activities (such as driving a car) challenging or impossible.

Persistent or recurrent vertigo, even if controlled by medications, is disqualifying for diving.

Return to diving after inner-ear barotrauma or DCS should be evaluated on an individual basis depending on the extent of permanent injury of inner-ear organs.

Tinnitus (Ears Ringing)

Tinnitus is noise or ringing in the ears.

Tinnitus is the sensation of an external sound that is not actually present. Tinnitus (ears ringing) affects approximately one in five people and can be caused by many medical conditions.

Tinnitus is the sensation of an external sound that is not actually present. Tinnitus (ears ringing) affects approximately one in five people and can be caused by many medical conditions.

Possible Diagnoses

It is important to find the underlying cause of the tinnitus. Acute tinnitus occurring during or after diving is likely related to ear barotrauma or inner-ear DCS. If associated with diving, your physician must determine whether it is barotrauma or inner-ear DCS, because the treatments are not the same, and administering the wrong one can be harmful.

Other possible causes of tinnitus include:

  • Concussion
  • High-intensity noise or blast
  • Infection
  • Ear infection (otitis media)
  • Tumor
  • Temporomandibular joint (TMJ) dysfunction
  • Foreign body in the ear
  • Vascular abnormality
  • Meniere’s disease
  • Hypertension
  • Migraine
  • Some medications (including aspirin and quinine)
  • Various poisonings (such as carbon monoxide, nicotine and heavy metal)

Fitness to Dive

If tinnitus is not related to diving and the underlying problem is not a contraindication for diving, there is no reason to curtail diving because of tinnitus itself.


Hearing Loss/Deafness

Hearing loss or deafness is the partial or complete loss of hearing from normal baseline.

Complete or partial hearing loss can occur for a variety of reasons. There are several diving-related causes including barotrauma, decompression sickness (DCS) and damage to the inner ear.

Hearing loss can be classified as conductive or sensorineural.

  • Conductive hearing loss involves the ear canal, eardrum and tiny bones of the middle-ear ossicles; these anatomical components mechanically conduct sound to the inner ear, where electrical signals are generated.
  • Sensorineural hearing loss involves the brain, the eighth cranial nerve or the inner ear.

Possible Diagnoses

There are many causes of hearing loss, including infection, blocked ear canal, barotrauma, drugs, trauma, round- or oval-window rupture, stroke, Meniere’s disease, noise and medications.

Fitness to Dive

Although uncommon, dive-related permanent hearing loss resulting from ear barotrauma or inner-ear DCS is possible. If the injury causes permanent unilateral (one ear only) hearing loss or impairment, most physicians will recommend against a return to diving. This is often recommended because if subsequent diving resulted in injury to the remaining functioning ear, the individual may experience permanent bilateral hearing loss. This recommendation applies to all monaural (one-sided hearing) individuals, regardless of the cause of unilateral hearing loss or impairment.

An additional population for whom diving is often discouraged or extreme caution is advised includes those who have undergone cochlear-implant surgery, ossicle surgery or tympanic-membrane repair (myringoplasty.) Diving places individuals with this medical history at risk of damaging the surgical repair, resulting in hearing loss. For divers who have undergone such procedures or suffered permanent hearing loss from ear barotrauma, extreme caution is often recommended, and close consultation with an ENT physician prior to diving is highly advised. For a referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.

It is important to mention that bilateral hearing impairment (either congenital or acquired) does not necessarily medically preclude someone from diving. However, in cases of bilateral hearing impairment, a diving environment may pose potential difficulties with surface communications, both with other divers and with crew members. Obstructed communications in cases regarding boat traffic, diver recall and other unforeseen circumstances may result in delayed emergency response, injury or death.

Next: Chapter 4 – Hygiene >

Chapter 4: Hygiene


People are aware of their ears in many ways. They take prominent place on the head, and thus aesthetic concerns sometimes compete with health concerns. Natural protection of the skin of the ear canal involves a wax, which in some cases may become a health nuisance and cause real medical issues. Some people perceive the wax as a hygiene issue and overzealously try to get rid of it. This can cause problems of its own.

Outdoors activities, especially water sports, expose ears to cold, wet and overly warm conditions, which can damage ears. There have been many proposed commercial solutions that supposedly will mitigate the risk of ear injury or damage. Unfortunately, few such products have been tested by health authorities. In this section, we will discuss aural hygiene and medications as well as earplugs (a device we do not endorse for divers) and ear ventilation tubes.

In this chapter, you’ll learn about:

Aural Hygiene

Having a clean ear canal is important for divers. In extreme cases, earwax can form a plug and trap air between itself and the eardrum, which can cause an “explosive” tympanic membrane perforation that tears outward instead of the more common inward perforation.

In addition, an earwax plug could prevent water from chilling one ear, while the other is naturally chilled by water filling the ear canal. This temperature differential between the two ears causes caloric vertigo.

Finally, a wax plug may prevent proper drainage from the ear canal. The retained moisture may cause softening of the skin and pave the road to infection.

So, how should you clean your ears?

The Wrong Ways

Avoid cotton-tipped swabs. The cotton-tip applicators may push wax deeper into the ear, making wax removal more difficult. In addition, the ends of the cotton-tip applicators can detach and be left in the ear canal. In a few days this usually results in a severe ear-canal infection. If this happens, the cotton should be identified and removed by a qualified physician. Do not ever attempt to do this yourself; you could tear your eardrum.

Handling Insect Infections

Occasionally, people who sleep outdoors or who live in warm areas can get insects in their ears. An insect in the ear can be an alarming experience. For removal, you’ll need a cool head, especially if the insect is still moving or stinging.

In the field, you can use rubbing alcohol, which rapidly drowns the insect and cleanses the ear canal. It is also acceptable to use a bulb syringe filled with a warm soapy water (such as baby shampoo) and hydrogen-peroxide solution. If this is unsuccessful, get medical help right away. The preferred method is removal by a qualified physician with special instruments and a microscope.

The Right Way


So, how should you clean your ears? When you bathe, occasionally wash your ears with a bulb syringe filled with warm soapy water and hydrogen-peroxide solution. On a diving trip, use a mixture of half white vinegar and half rubbing alcohol after a day’s diving; this serves to cleanse and dry the ear canal as well as change the pH balance to make the area less prone to bacterial infection. This can also help prevent swimmer’s ear (otitis externa).

If you have a hard time getting water out of your ears, try using a hair dryer. It’s a good idea to lift the ear upward and back to straighten the ear canal and then to blow warm dry air into the ear canal for five minutes. Take special care to ensure the air is not too hot.

Remember that ear care is as basic and important as the care of any of your other diving equipment.


Earplugs are devices that occlude the external ear canal. They are primarily used to block the pressure of water on the eardrum. Generally, earplugs should not be used by divers.

Procedure in Practice


Standard solid earplugs create an air space that cannot be equalized while diving, making them generally unsafe for diving; however, some divers use earplugs in special situations.

The main concern is that water pressure could wedge the plug into the ear canal. If this occurs, there is risk of external ear barotrauma. To address these concerns, some manufacturers promote the vented earplug, which has a small hole for venting between the water and the ear canal. The holes typically have a valve for pressurization without letting water enter the ear canal.

Most manufacturers of vented plugs emphasize the ease with which their products equalize and recommend that divers clear their ears frequently while wearing the earplugs to maintain proper pressurization. However, these assertions have not been independently tested. There is not enough data or evidence to recommend the use of plugs for divers. The risks of complications underwater from malfunction or removal of an earplug are real and can potentially place the diver at increased risk for injury.


Eardrops are a solution of medications intended for application in the external ear canal.

Prophylactic Use of Eardrops

For most divers, eardrops are not necessary after diving. The purpose of most eardrops is to prevent external ear canal infections (known as otitis externa or swimmer’s ear). Infections of the ear canal are associated with persistent moisture as well as local skin trauma, which can result from inserting cotton swabs or other objects into the ears that can damage the thin skin lining the ear canal. As DAN medical information specialists are fond of saying, “Don’t put anything smaller than your elbow in your ear.” Persistent moisture and local skin trauma can enable bacterial overgrowth and infection.


Eardrops are formulated to help dry the ear after exposure and lower the acidity (pH), making the external ear canal an unfriendly environment for bacterial or fungal colonization and infection. Common ingredients include acetic acid (the active ingredient in vinegar), boric acid, aluminum acetate, sodium acetate, isopropyl alcohol and glycerin. The acids alter pH, which retards bacterial growth; aluminum acetate and sodium acetate are astringents, which shrink tissues. Isopropyl alcohol helps dry the tissues, and glycerin may help lubricate the skin to prevent excessive drying.

For divers plagued by swimmer’s ear, gently rinsing the ears with freshwater after each dive may help. Drying the ears with a hair dryer may also be helpful, but take care to ensure the air is not too hot.

Therapeutic Use of Eardrops

Eardrops can be prescribed by your physician to treat infection or inflammation of the external ear canal. These drops may contain antibiotics and/or steroids.

Note: It is important to never put drops into the ear canal if eardrum rupture is suspected. Normally the eardrum serves as a barrier to the middle-ear space. If ruptured, contamination or medications harmful to the inner ear can gain access.

Fitness to Dive

Prophylactic ear drops are used to prevent external canal infections during repetitive multiday diving. If you feel ear pain, you should stop diving and have your ear evaluated. Divers diagnosed with an ear infection or ear injury should not dive before fully healed and cleared by a physician.

Ear Ventilation Tubes

Ear ventilation tubes are small tubes that are surgically inserted through the eardrum to enhance drainage and equalization.



Small ventilation tubes may be surgically inserted through the eardrum (tympanic membrane) to help interrupt a cycle of repetitive middle-ear infections. The infection process causes swelling and inflammation in the Eustachian tubes, preventing proper drainage; the ventilation tubes enable drainage from the middle ear until the Eustachian tubes normalize. Inserting the ventilation tubes through a small incision in the tympanic membrane (myringotomy) usually corrects this situation.

The tubes are not meant to be permanent implants and usually fall out on their own or are removed by the physician. The small incision usually heals shortly after the tubes are removed. In rare cases, a small hole may remain if the tubes are left in for a long period of time. This situation can be tested for and is best addressed by your physician. It is unlikely that the tubes are still in place after more than a few years.

Fitness to Dive

Diving is not recommended while the tubes are in place as they will allow water to enter the middle ear, risking vertigo and infection. After the ventilation tubes are removed or come out, adequate time for healing must be allowed (at least six weeks). Middle-ear and Eustachian tube function must be confirmed as normal before diving
is considered.

A bigger problem may be scarring of the Eustachian tubes as a result of the chronic ear infections. This can make ear equalization difficult for the diver. Currently, there is no surgical procedure that can correct a partially obstructed Eustachian tube.

Children and adults alike need immediate attention for symptoms of middle-ear infection and barotrauma. Symptoms may include but are not limited to pain; ringing or roaring in the ears (tinnitus); a sensation of partial, decreased or muffled hearing; and drainage from the ear canal.

Next: Chapter 5 – Medical Conditions >

Chapter 5: Medical Conditions


Your ears and ability to equalize may be affected by various diseases. In this section, we have provided information about two conditions divers often ask about: Meniere’s disease and deviated nasal septum. If you have questions about specific conditions that are not highlighted in this book, do not hesitate to contact the DAN Medical Information Line at +1 (919) 684-2948.

In this chapter, you’ll learn about:

Meniere’s Disease

Meniere’s disease is a disorder involving recurring episodes of vertigo, which may be associated with vomiting, fluctuating hearing loss, ringing in the ears (tinnitus) and a sensation of increased pressure in the ear.


This chronic condition affects the inner ear. It results in vertigo and hearing dysfunction. A disabling episode of vertigo may involve severe nausea and vomiting. In addition, Meniere’s disease can muffle or impair hearing. Individuals may also experience a sensation of increased pressure in the ear. Migraine headaches have also been linked to this condition.


Treatment focuses on symptom management. Medications are used to control the vertigo and associated nausea and vomiting. Diuretics are sometimes used to help regulate the excess volume of endolymph (fluid contained in the inner ear) that is associated with Meniere’s disease.

An ENT physician consultation is recommended as surgical procedures may help achieve relief. For a referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.

Fitness to Dive

This condition is variable. It may spontaneously resolve or progress to involve the other ear. If you are at risk of experiencing disabling symptoms such as vertigo, disorientation, nausea or vomiting, you should not dive; should these symptoms occur underwater, they may lead to panic, choking and even drowning. In addition, these symptoms may be confused with dive-related injuries such as inner-ear barotrauma or inner-ear decompression sickness.

Deviated Septum

A deviation of the wall separating the two nostrils that may lead to obstruction of the nasal passages and sinuses is a deviated septum.

The nasal septum is the wall that separates the two nostrils. When the septum is displaced or curved, it is known as a deviated septum. Generally this condition is of little or no consequence and may go unnoticed; affected individuals may experience difficulty equalizing. A deviated septum may be present at birth (congential disorder) or result from trauma to the nose. It is often discovered during a routine physical exam. This condition has been linked to sinusitis as well as barotrauma (sinus and middle ear).



Decongestants may provide some relief. Surgical correction (septoplasty) is typically reserved for those with symptoms such as snoring, nasal obstruction, recurrent sinusitis or sleep apnea.

Fitness to Dive

There is no contraindication to diving with an asymptomatic deviated septum. If recurrent infections or difficulty equalizing occurs, an ENT consultation is suggested. For a referral in your area, email , or call the DAN Medical Information Line at +1 (919) 684-2948.

Decompression Sickness


Decompression sickness (DCS) is an unwanted outcome of diving. Measures to mitigate the risk of DCS have to be a part of every dive. This booklet provides updated concepts of causes and mechanisms, typical manifestations, standard management and prevention of DCS.

In this book, you’ll learn about:

Chapter 1 – Introduction to Decompression Sickness
The Physiological Mechanisms of DCS
Predicting Gas Uptake and Elimination

Chapter 2 – Effective Use of Your Dive Computer
Important Cautions
Basic Guidelines
Specific Tips and Tricks

Chapter 3 – Diagnosing Decompression Sickness
Signs and Symptoms of DCS
Differential Diagnosis of DCS

Chapter 4 – Treating Decompression Sickness
On-the-Scene First Aid
Subsequent Evaluation
Hyperbaric Oxygen Therapy
In-Water Recompression
Emergency Resources

Chapter 5 – Factors Contributing to Decompression Sickness
Thermal Stress
Optimal Practices
Postdive Air Travel
Medical and Physical Fitness
State of Hydration
Breathing Gas Mixture
Carbon Dioxide Level
Patent Foramen Ovale
Additional Factors

Chapter 6 – Summary and Closing Thoughts



Managing Editor: Petar Denoble, MD, DSc
Author: Neal Pollock, PhD

Chapter 1: Introduction to Decompression Sickness


One of the hazards associated with underwater diving is decompression sickness (DCS), caused by uncontrolled release of gas from tissues during or after surfacing.”

Diving is a popular recreational pastime as well as an activity with numerous practical applications in the scientific, commercial, military and exploration realms. While diving can be done safely, it is essential for all divers — no matter what their reason for diving — to appreciate that the underwater environment is unforgiving. Problems may arise during a dive due to insufficient medical or physical fitness, improper use of equipment or inadequate management of the high-pressure environment.

One of the hazards associated with the pressurized underwater setting is decompression sickness (DCS), a condition also known as “the bends.” This chapter explains the basics of DCS, while subsequent chapters provide details regarding its manifestation and management, risk factors that may predispose you to the condition and preventive steps that you can take to minimize your chance of developing it.

In this chapter, you’ll learn about:

The Physiological Mechanisms of DCS

Tissue Tension

When a diver is exposed to an environment of elevated pressure, inert gases (nitrogen, for example) accumulate in tissues. The deeper a dive is, the faster the body’s absorption, or “uptake,” of such gases. When the diver ascends, the drive is reversed, and gas leaves tissues. A diver’s ascent must be controlled to allow for an orderly elimination, or “washout,” of the accumulated gas. A slow ascent, conducted either continuously or in stages, usually allows for safe decompression, whereas a too rapid ascent following gas accumulation can sometimes result in DCS.

Air pressure increases slowly from zero at the boundary of space to one atmosphere (14.7 psi) at sea level; water pressure increases much more dramatically, adding one atmosphere of pressure for every 33 ft of seawater.

The concentration, or “tension,” of dissolved inert gas within your body’s tissues is a function of ambient pressure — that is, the pressure of the environment surrounding you at any given time. The inert gases that are not used in your body’s metabolic reactions normally exist in equilibrium with your ambient environment — in the same concentration as in the air around you. Tissues under such conditions are described as “saturated.” Minor pressure changes, such as those created by shifting weather conditions, produce minor pressure variations in atmospheric gases that are then matched by pressure changes in the gases in the body’s tissues. When a pressure difference, or “gradient,” is created, molecules from the area of higher concentration flow toward the area of lower concentration until balance is re-established. Since all of us constantly experience minor changes and corrections of this nature, the gas tension in our bodies is in a state of dynamic, rather than static, equilibrium — even before diving is added to the equation.


The diving environment puts a significant additional burden on this adaptive mechanism. Here’s why: Pressure is measured using a unit known as an “atmosphere.” There is no actual physical boundary between the Earth’s atmosphere and space, but the atmosphere is often considered to extend 62 miles (100 kilometers) from sea level to the edge of outer space. The pressure produced by this entire column of gas acting at sea level is one atmosphere, equal to 14.7 pounds per square inch (psi) or 101.3 kilopascals (kPa). By comparison, the change in pressure underwater increases by one atmosphere for every 33 feet of saltwater and every 34 feet of freshwater. As a result, any variation you experience in surface atmospheric pressure is extremely modest compared with the variation in pressure you can undergo when you travel vertically underwater; this can create huge gradients in the uptake of gases during your descent and in their elimination during your ascent.

Gas Exchange

Your lungs serve as the primary connection between your body and the environment in which you are situated at any given time. When you expose yourself to increased pressure underwater, the gas in your lungs is compressed. This creates a gradient from your lungs to your bloodstream and, subsequently, from your bloodstream into your tissues as they are perfused, or supplied, with oxygenated blood. Your tissues will take up inert gas until the gradient is eliminated, an effective state of equilibrium, or saturation, with the surrounding environmental pressure. It takes a long exposure for complete saturation to be reached, but once reached, staying longer does not further increase gas uptake or the required decompression.

Predicting Gas Uptake and Elimination

Tissue Compartments

This natural physiological mechanism can be predicted by a series of mathematical algorithms based on “half-time compartments,” which approximate the exponential uptake and elimination patterns expected in various types of perfused tissues. The key to these algorithms is that different parts of the body take up and eliminate inert gases at differing rates — for example, blood is considered a “fast compartment” and bone a “slow compartment.” (The term “compartment” is not meant as an exact referent for these tissues but, rather, as a mathematical construct to estimate what happens in various parts of the body.)

The fastest tissues are the lungs, which achieve equilibrium almost instantly. Blood follows in speed, then the brain. The slowest tissues are those that are relatively poorly perfused, such as ligaments and cartilage, or those that have a high capacity for inert gas uptake, such as fat in poorly perfused areas. The reason for using a mathematical algorithm to estimate tissue status is that it is not yet practical to directly measure uptake or elimination in specific tissues.

For a theoretical tissue with a half-time of 10 minutes, 50 percent of the difference is eliminated in the first 10 min, then 25 percent in the next 10 min (half of the remaining 50 percent), then 12.5 percent in the next 10, and so on.

An example may demonstrate how the algorithms work. Let us imagine a diver who has been instantly displaced from the surface to a fixed depth — effectively, a fixed pressure — and let us say that in this particular dive scenario, a fast compartment has a half-time of five minutes. In such a case, the first five minutes of exposure to the higher pressure would result in sufficient inert gas uptake to eliminate half of the difference produced by the pressure gradient (50 percent, in other words); this is the steepest portion of the uptake curve. The second five-minute period would eliminate half of the remaining difference (another 25 percent). The third five-minute period would eliminate half of the remaining difference (12.5 percent); the fourth, 6.25 percent; the fifth, 3.125 percent; and so on. This exponential pattern means that the rate of change becomes progressively slower as the magnitude of the difference decreases. The example described a fast compartment; half-times for slow compartments have been computed in some algorithms out to almost 500 minutes. In decompression theory, the absolute difference in pressure is immaterial — the same half-time construct applies to any gradient. With no additional influences on the process, equilibration, or saturation, would be achieved in a period equal to about six half-times. As gas dissolves in the tissue, the difference between the external pressure and internal pressure decreases, reducing the driving force.

Most dives do not last long enough for the diver to reach saturation — these are known as “bounce dives.” During such exposures, the inflow gradient exists throughout the descent and bottom phase of the dive, which causes continued uptake of inert gases, certainly in the body’s slow compartments and probably in intermediate compartments. When the diver starts to ascend, and the ambient pressure starts to drop, the gradient begins to reverse — first in fast compartments and then in progressively slower compartments.

Degree of Supersaturation

Effectively, during and after surfacing, most of a diver’s tissues will be supersaturated in comparison with the ambient pressure. If the degree of supersaturation is modest, inert gases can travel in an orderly manner from the body’s peripheral tissues into the blood and then to the lungs, from where they can be exhaled to the atmosphere. But if the degree of supersaturation is too great, the elimination of inert gases becomes disorderly. In this case, gas bubbles can form in the tissues of the diver’s body.

Bubble formation does not always cause problems, but the higher the gradient, or degree of supersaturation, the greater the likelihood that signs and symptoms of DCS can occur. 


It is a dangerous misconception that measurable bubbles form after all dives and are of no importance. But at the same time, it is a misconception that bubbles visualized in the blood stream in and of themselves signal DCS. The formation of gas bubbles during decompression represents a stress greater than is optimal and may lead to DCS. It is best to follow conservative dive profiles to minimize the likelihood of bubble formation. The greatest difficulty is in knowing what counts as “conservative,” since most divers have never been monitored for bubbles, and uptake and elimination is altered by a number of factors in addition to the pressure-time profile.

The half-time compartment calculations are used to generate exposure-limit predictions for a range of hypothetical compartments. In paper or plastic form these are known as “dive tables.” Modern dive computers allow for much more flexible guidance since they are able to continuously monitor the pressure-time profile and simultaneously compute the status of a variety of theoretical tissue compartments. But in reality, the picture is much more complex. Gas exchange is influenced by more than just the pressure-time profile. So while it is important for divers to understand the concepts behind calculating half-time compartments, divers must also keep in mind that a wide range of factors can influence gas uptake and elimination and effectively alter decompression risk. Thus the onus is on the diver not to rely too heavily on a table or device for safety.

Next: Chapter 2 – Effective Use of Your Dive Computer >

Chapter 2: Effective Use of Your Dive Computer


“Divers are surprised when symptoms of DCS develop after dives that appeared safe according to their dive computers. Remember, models reflect an average diver, not you.”

In recent years, dive computers have supplanted dive tables as the primary means of regulating dive profiles. Dive computers offer an advantage in that they enable the diver to dynamically establish different compartments as the controlling compartment, as conditions change during a dive. In reality, the compartments in a dive computer’s modeling software do not have to represent any particular tissue, as long as the guidance provided by the model results in an acceptable outcome — specifically, very little DCS.

In this chapter, you’ll learn:

Important Cautions


While the guidance provided by decompression models can be very useful, it is important for divers to keep in mind that dive schedules — whether they are presented in printed tables or on the screen of a dive computer — are limited in what they measure and in the assumptions upon which the model was constructed. Tissue compartment parameters can be adjusted, or new compartments can be added to an algorithm, if experience shows deficiencies in a given model — but in real time, the calculations are limited by the variables that are being processed. Algorithms can estimate limits based on time and pressure (depth) profiles for a given breathing gas, but they are not able to compute the impact of myriad real-time factors, including thermal status, exercise intensity, joint forces and a host of individual predispositions that are currently not well understood, let alone quantifiable in their impact on decompression stress.

Divers are often surprised when symptoms of DCS develop after dives that were conducted within the limits of their dive computers. It is important to remember, though, that while mathematical models predict outcomes, they do not guarantee them. The fact that a dive was conducted within the limits suggested by a dive computer (or a dive table) does not make a DCS hit “undeserved.” The mathematical algorithms provide guidance that must be evaluated and tempered by a thoughtful diver.

Many divers are also unaware of the fact that dive computers make use of many different mathematical models, or versions of different models; there is no universal standard. A single manufacturer may even use more than one model, possibly in a single type of computer. This makes it extremely difficult to assess the nuances of every system.

Basic Guidelines


There are some basic guidelines that can help to ensure the safe and effective use of a dive computer. The following considerations are intended to offer a somewhat light-hearted insight into what your dive computer can — and cannot — do.

It is helpful to think of your dive computer in these ways:

  • As a business competitor: Master it by learning its strengths and weaknesses.
  • As a date: It must be turned on for the relationship to work.
  • As a buddy: It should descend and ascend whenever, but only when, you do.
  • As a personal assistant: It reminds you of rules and schedules you might otherwise forget.
  • As an actor: It recites the lines without having to understand their implications.
  • As a politician: Do not believe everything it tells you.
  • As a hotel concierge: It will help you do what you want — but at a price.
  • As a stranger: It knows virtually nothing about your personal reality.
  • As a mate: Is it compatible with your friends?
  • As a news reporter: It will air your dirty laundry.
  • As a tool: Use it appropriately.

Specific Tips and Tricks

Push the Right Buttons


You should know not only which buttons to push to make your computer work, but also which mathematical model or model derivation it employs in making its decompression computations. There is a surprising range in models, from conservative to liberal, and these differences may not be evident at first glance. For example, a computer may establish conservative limits for an initial dive but liberal limits for repetitive diving. It is best to learn enough about the various available models and derivations before you select a dive computer, so you are sure to choose one that is compatible with your own level of risk tolerance. Choosing one purely based on familiarity may not be the best strategy. Even if you have had good outcomes on previous dives with a computer, it does not guarantee that it will be the best one for your future diving. Accumulating knowledge takes commitment, but informed planning for decompression safety should be a top concern.

Tune In and Turn On

Failing to turn on your dive computer (or to take it with you on a dive) may sound like a joke, but it does happen and can create real problems. No computer can factor in the exposure profile of a previous dive if it was not there. And any decompression model is invalid unless you start using it when you are “clean” — fully off-gassed from any previous dives. If you forget to take your computer with you on a dive early in a repetitive series, you are then restricted to using tables for the duration of that series (assuming that you are able to manually compute the exposure of the unmonitored dive). And do not even think about hanging your computer on a downline during a surface interval in an effort to compensate for having forgotten it on an earlier dive; there may be stories about that happening, but it is not a responsible practice.

Use It Appropriately

The only person who does not have to worry about taking a dive computer on every dive is the one who uses it solely as a datalogger — that is, only to record time and depth information instead of to calculate decompression profiles. Remember, however, that using your computer simply to log your time and depth data means that you must still plan all your dives using dive tables and must recompute your repetitive group status afterward, as appropriate. You cannot move in and out of relying on your computer’s decompression computations unless it has recorded all of your exposure profiles.

Remember Its Limitations

Dive computers are wonderful at carrying out programmed mathematical computations, but they are blind to the many insights you may have before, during and between your dives. For example, your dive computer knows nothing about your personal health status, your level of physical fitness or your individual susceptibility to decompression stress. It also knows nothing about your thermal stress or physical efforts during or between dives. The fact that many dive computers display water temperature might suggest that thermal stress is factored into the device’s algorithms. A water temperature reading, however, provides no useful information regarding thermal stress, since the diver carrying the device could be wearing anything from a bathing suit to a wetsuit without a hood to a cold-water drysuit with a hood, gloves and cold-water undergarments. More important, it is not yet possible to directly compute the impact of differences in thermal status during different parts of a dive, even if the computer was able to measure the diver’s core temperature and skin temperature in key spots.

We do know that being warm (rather than cool or cold) during the compression and bottom phase of a dive promotes inert gas uptake (not optimal), and that being warm during the decompression phase promotes elimination (optimal). While impractical for the comfort-loving diver, decompression safety is optimized by being neutral or cool during the inert gas uptake phase of descent and bottom time and warm during the inert gas elimination phase of ascent. While the concept of thermal changes on decompression stress is clear, we are still years away from being able to quantify the real-world effects of these factors for dive-planning purposes. Similarly, while some computers are able to track gas consumption, we have much to learn before this information can be meaningfully incorporated into decompression models. Variations in air consumption can reflect differences in the depth of a dive or in the diver’s experience, level of anxiety or degree of physical exertion. The bottom line is that interpreting the precise physiological impact of the interactions among these diverse factors is exceedingly difficult, requiring thoughtful practice by divers.

Heed Your Computer’s Readings

Divers need to pay attention to their dive computers if the information provided is to be of any use. Be aware that confirmation bias can promote risky behavior. “Getting away with” a risky exposure once, twice or even many times may eventually catch up with you. It may not truly be safe for you or for a partner who might have a higher degree of susceptibility to decompression stress. Those who wish to worry less about their exposure will have greater peace of mind if they choose a computer that employs an extremely conservative decompression model. It is also important to pay attention to your dive computer. If you are diving with a group, do not forget that there can be considerable variability in the guidance provided by different computers or computers with different user-selected settings. That means there is considerable benefit in diving with others who use a computer with a similar decompression model and settings, because if modest discrepancies arise, following the most conservative directive will likely not be terribly burdensome for the group. But if members of a group are using dive computers with substantially different models, and each diver wishes to follow his or her own device, it can lead to a breakdown in the buddy system.

Do Not Rely Blindly On Your Computer

Although heeding your computer is important, do not take its advice unthinkingly. The same profile can sometimes be conducted without problem again and again, right up to the dive where it does not prove safe. Divers often try to blame a specific factor, such as dehydration, for the development of symptoms following one dive but not another. This approach is not productive. The range of variables in play during a dive are rarely identical, and there is a probabilistic element to decompression risk — that is, chance can play a role in the manifestation of DCS.

The best approach is to avoid the extremes of either fatalistic resignation or smug focus on a single supposed magic bullet. There are many, many small steps you can take to make any dive safer. The most important one is to stay within a reasonably conservative time-depth profile and to add safety stops to every dive. Other important steps are to minimize your exercise intensity and avoid overheating during the gas-uptake phase of your dive, to choose the right breathing gas, to practice enough that you are able to perfectly control your buoyancy, to remain well-rested and well-hydrated, choose more conservative user-adjustable settings on the computer, and to dive with a partner who has similar goals and follows similar practices. Adding small safety margins to each step can help to provide a comfortable security cushion. Dive computers are powerful tools, but sound knowledge of diving physiology, good physical conditioning and adherence to thoughtful practices offer the best protection for divers.

Keep It With You

If you do develop DCS symptoms, you should keep your computer with you when you go for medical evaluation. Some facilities may have the ability to download or review your profile to aid in the evaluation of your case. The medical staff will surely appreciate seeing confirmation of your description of the events that precipitated your symptoms.

Next: Chapter 3 – Diagnosing Decompression Sickness >

Chapter 3: Diagnosing Decompression Sickness


“While DCS is commonly thought of as a bubble disease, bubbles are probably only the gateway to a complex array of consequences and effects.”

DCS may develop when a diver’s degree of supersaturation is so high (or, stated another way, if the elimination gradient is so steep) that a controlled transfer of inert gases from the body’s tissues to the bloodstream — and then from the bloodstream to the lungs and the lungs to the environment — is not possible. If that removal process is inadequate, inert gases will come out of solution and form bubbles that can distort tissues, obstruct blood flow, cause mechanical damage (to the joints, for example) and/or trigger a cascade of biochemical responses.

Although much is known about DCS, its mechanisms of insult are still being investigated. And while DCS is commonly thought of as a bubble disease, bubbles are probably only the gateway to a complex array of consequences and effects.

In this chapter, you’ll learn about:

Skin mottling like this is characteristic of cutis marmorata, a condition that can warn of likely development of more serious Type 2 symptoms.

Signs and Symptoms of DCS

The collective insult to the body’s systems can produce symptomatic DCS. The condition’s primary effects may be evident in the tissues that are directly insulted. Its secondary effects can compromise the function of a broad range of tissues, further jeopardizing the diver’s health.

The ability to recognize the signs, or objective evidence, and the symptoms, or subjective perceptions, of DCS — and to differentiate them from signs and symptoms less likely to be associated with DCS — is important. A variety of classification systems have been established for DCS. One common approach is to describe cases as Type 1 or Type 2.

Type 1 DCS

Type 1 DCS is usually characterized by musculoskeletal pain and mild cutaneous, or skin, symptoms. Common Type 1 skin manifestations include itching and mild rashes (as distinct from a clear mottled or marbled and sometimes raised discoloration of the skin — a condition that is known as cutis marmorata that may presage the development of the more serious symptoms of Type 2 DCS). Less common but still associated with Type 1 DCS is obstruction of the lymphatic system, which can result in swelling and localized pain in the tissues surrounding the lymph nodes — such as in the armpits, groin or behind the ears.

Collage showing pain at several part of body

The symptoms of Type 1 DCS can build in intensity. For example, pain may originate as a mild ache in the vicinity of a joint or muscle and then increase in magnitude. However, the pain associated with DCS does not typically increase upon movement of the affected joint, although holding the limb in one position rather than another may reduce discomfort. Such pain can ultimately be quite severe.

Type 2 DCS

The Romberg test evaluates postural control. The sharpened Romberg, which includes crossing the arms and putting one foot in front of the other, is more sensitive to changes in static balance.

Type 2 symptoms are considered more serious. They typically fall into three categories: neurological, inner ear and cardiopulmonary. Neurological symptoms may include numbness; paresthesia, or an altered sensation, such as tingling; muscle weakness; an impaired gait, or difficulty walking; problems with physical coordination or bladder control; paralysis; or a change in mental status, such as confusion or lack of alertness. Inner-ear symptoms may include ringing in the ears, known as “tinnitus”; hearing loss; vertigo or dizziness; nausea; vomiting; and impaired balance. Cardiopulmonary symptoms, known commonly as “the chokes,” include a dry cough; chest pain behind the sternum, or breastbone; and breathing difficulty, also known as “dyspnea.” The respiratory complaints, which are typically due to high bubble loads in the lungs, can compromise the lungs’ ability to function — threatening the affected diver’s health, and even life, if treatment is not sought promptly.

Type 2 symptoms can develop either quickly or slowly. A slow build can actually obscure the seriousness of the situation, by allowing denial to persist. For example, fatigue and weakness are common enough concerns, especially if their onset is protracted, that they can be very easy to ignore. Less common symptoms, such as difficulty walking, urinating, hearing or seeing — especially if their onset is quick — can sometimes prompt faster recognition of the existence of a problem. It is fair to say that divers can initially be reluctant to report symptoms, though they usually will do so if their symptoms do not go away. This is a shortcoming divers should be aware of, lest they fall prey to it.

Presentation of DCS

The presentation of DCS is frequently idiosyncratic — that is, its “typical” pattern can be atypicality. In some cases, an affected diver’s chief complaint may draw attention away from more subtle but potentially more important symptoms. The following list ranks the initial manifestations of DCS, from those most commonly to least commonly reported (Vann et al. 2011):

  • Pain, particularly near the joints
  • Numbness or paresthesia
  • Constitutional concerns — such as headache, lightheadedness, unexplained fatigue, malaise, nausea and/or vomiting, or anorexia
  • Dizziness or vertigo
  • Motor weakness
  • Cutaneous, or skin, problems — such as an itch, rash, or mottling (“cutis marmorata”)
  • Muscle discomfort
  • Impaired mental status
  • Pulmonary problems — such as breathing difficulties (“the chokes”)
  • Impaired coordination
  • Reduced level of consciousness
  • Auditory symptoms — such as hearing sounds that are not there or having a hard time hearing
  • Lymphatic concerns — such as regional swelling
  • Bladder or bowel dysfunction — such as retention of urine
  • Compromised cardiovascular function

According to this recent review, pain and numbness, also known as paresthesia, were reported initially in nearly two-thirds of cases of DCS, constitutional symptoms in approximately 40 percent of cases, dizziness/vertigo and motor weakness in approximately 20 percent, and cutaneous symptoms in approximately 10 percent (Vann et al. 2011).

Differential Diagnosis of DCS


DCS is a high-profile diving injury because of its potential severity. But divers need to remember that not all diving-related problems turn out to be DCS. When two or more conditions have overlapping symptoms, as is the case with many diving-related injuries, differential diagnosis is the process by which medical personnel figure out which of the potential conditions is most likely responsible for the symptoms.

The term decompression illness (DCI) was coined to encompass both DCS and the related condition known as arterial gas embolism (AGE), the latter arising from barotrauma of the lungs that introduces gas into the systemic bloodstream. Some of the other conditions and circumstances that involve similar symptoms include inner-ear barotrauma; middle-ear or maxillary sinus overinflation; contaminated breathing gas; oxygen toxicity; musculoskeletal strains or trauma sustained before, during or after a dive; marine life envenomation; immersion pulmonary edema; water aspiration; and coincidental neurological disorders, such as stroke (Vann et al. 2011). Thermal stress — sometimes due to excessive heat, but usually due to cold exposure — can also be responsible for similar symptoms. In some cases, a careful medical history can easily rule out one diagnosis or another. For example, symptoms of immersion pulmonary edema often develop at depth. In such a case, a good history would rule out DCS, which only develops after significant decompression stress during ascent.

It is essential for divers with any of these symptoms to seek medical evaluation and support. While first responders are able to perform initial analysis of an injured individual, such as administering a field neurological assessment, the capabilities of nonphysicians do not come close to the clinical skills and insights held by experienced clinical specialists.

Next: Chapter 4 – Treating Decompression Sickness >

Chapter 4: Treating Decompression Sickness


“If signs or symptoms consistent with DCS develop, initiate appropriate first aid and contact the nearest emergency medical services. For additional emergency assistance contact DAN +1-919-684-9111.”

There are several elements to the effective management of DCS, specifically on-the-scene evaluation and first aid, transport and definitive medical evaluation and treatment. Anyone who has suffered DCS should seek appropriate evaluation, and possibly ongoing care, from a physician well informed about diving-related medical issues.

In this chapter, you’ll learn about:

On-the-Scene First Aid

The foundation of first aid is basic life support. The primary first aid measure for DCS is delivery of supplemental oxygen in the highest concentration, or fraction, that is practical (Longphre et al. 2007). High oxygen fractions, if provided rapidly and over a sustained period, can reduce or even eliminate symptoms of DCS, albeit often only temporarily if definitive treatment is not secured. Continuous-flow oxygen systems, using non-rebreather or pocket masks, are frequently available in diving environs; however, such equipment delivers modest oxygen fractions. Much higher fractions can be achieved with demand masks, though they are appropriate only for conscious individuals able to breathe on their own.

A variety of different masks can be used with oxygen systems.
DAN experts developed this remote emergency oxygen (REMO2) surface oxygen rebreather for first-aid use (Pollock and Natoli 2007).

Rebreather systems are another on-the-scene option; such systems permit the unused oxygen in the diver’s exhalations to be recycled, or rebreathed. A rebreather apparatus can thus provide high fractions with minimal gas use and may prove especially helpful in settings where the supply of oxygen is limited (Pollock 2004; Pollock and Natoli 2007).

Chemical oxygen generating systems — devices with a long shelf life that deliver oxygen via a chemical reaction — may in some situations be the only option available. However, if emergency medical services are not readily accessible, such devices are unlikely to provide a sufficient oxygen supply (Pollock and Natoli 2010).

Subsequent Evaluation

First aid is just the first step in treating an affected diver. Anyone who has experienced symptoms associated with DCS is advised to seek subsequent medical evaluation. This should occur even if the diver’s symptoms improved or disappeared upon the administration of oxygen, since subtle issues can be missed or symptoms can return once oxygen delivery is stopped. For the same reason, it is advisable to seek input from an experienced dive-medicine specialist — someone aware of all the nuances in the presentation, course and treatment of DCS.

Hyperbaric Oxygen Therapy

The definitive treatment for DCS is hyperbaric oxygen (HBO) therapy, or the delivery of pure oxygen at a pressure substantially higher than that of atmospheric pressure. HBO therapy reduces the size of any bubbles and improves gradients which promote oxygen delivery and inert gas elimination. HBO therapy is typically delivered in recompression chambers.

This is a monoplace hyperbaric chamber — able to hold a single patient, without any inside support personnel, or “tenders.”

A common HBO regimen is the U.S. Navy Treatment Table 6 (USN 2008). According to this regimen, the hyperbaric chamber is initially pressurized to 2.8 atmospheres absolute (ATA), equivalent to the pressure found at 60 feet (18 meters) of seawater. The patient breathes pure oxygen, interspersed with scheduled periods of breathing regular air to reduce the risk of oxygen toxicity. The usual duration of the USN TT6 treatment is just under five hours, but extensions can be added as required, based on the patient’s response.

This is a small multiplace and multilock hyperbaric chamber; it can hold multiple patients plus inside tenders. Personnel or equipment can be transferred into or out of the chamber while treatment is ongoing.

HBO treatment can be conducted in a monoplace chamber, often an acrylic tube sized to hold just one patient, or in a multiplace chamber, sized to accommodate one or more patients plus one or more “tenders” — that is, technicians or other medical personnel. Multilock chambers are designed to allow patients, tenders or equipment to be transferred into and out of the chamber while treatment is ongoing.

The course of HBO therapy will vary according to the particulars of each case; both the presentation of DCS and its response to treatment can be idiosyncratic. A full resolution of DCS symptoms can often be achieved with one or sometimes multiple HBO treatments. In some cases, however, resolution will be incomplete, even after many treatments. The normal clinical approach is to continue the treatments until no further improvement is seen in the patient’s symptoms. Modest residual symptoms will then often resolve slowly, after the treatment series is ended. Full resolution of symptoms can sometimes take months to achieve and in some instances may never be realized.

This is a large multiplace and multilock hyperbaric chamber, in which multiple pressure exposures can be conducted simultaneously.

In-Water Recompression


In-water recompression may be an alternative to chamber recompression in remote locations, if there is neither a nearby chamber nor the means to quickly transport the patient to a chamber elsewhere. The technique involves bringing the diver underwater again, to drive gas bubbles back into solution to reduce symptoms and then slowly decompress in a way that maintains an orderly elimination of the excess gas.

While in-water recompression is simple in concept, it is practical only with a substantial amount of planning, support, equipment and personnel; appropriate water conditions; and suitable patient status. Critical challenges can arise due to changes in the patient’s consciousness, oxygen toxicity, gas supply, and even thermal stress. An unsuccessful in-water recompression may leave the patient in worse shape than had the attempt not been made. The medical and research communities are divided on the utility of in-water recompression. It is beyond the scope of this publication to consider all of the relevant factors, but it is fair to say that there are probably more situations when in-water recompression should not be undertaken than situations when it would be a reasonable choice.

As a general rule, a diver who develops symptoms consistent with DCS should be removed from the water, and first aid should be delivered on the surface, even if there is likely to be a delay before definitive medical care can be sought.

Emergency Resources

The best course of action, if signs or symptoms consistent with DCS (or any other serious injury) develop, is to initiate appropriate first aid and then immediately contact the nearest emergency medical services (EMS). The next step should be to contact DAN to seek advice regarding the proper progression of care. The organization’s emergency hotline number is +1-919-684-9111.

It is generally not appropriate to show up unannounced at the nearest hyperbaric chamber. This could mean bypassing a facility where the victim might be able to receive a more thorough and appropriate evaluation. Remember that not all injuries associated with diving are DCS, even if it seems so in the heat of the moment. In addition, the chambers at some facilities are not available to treat divers at all times or ever. One of the challenges within North America is the shrinking number of hyperbaric chambers that accept diving casualties, particularly outside normal business hours.

The key point to remember is that establishing contact with emergency medical services and DAN can ensure timely and appropriate case management. When in doubt, call.


  1. Tell the operator you have a dive emergency. The operator will confirm your name, location and phone number, and ether connect you directly with DAN medical staff or have someone call you back at the earliest possible moment.
  2. The medical staff member may make an immediate recommendation or call you back after making arrangements with a local physician
  3. The medical staff member may ask you to wait by the phone while arrangements are being made. These plans may take 30 minutes or longer, as complex coordination is often required. If the situation is life-threatening, arrange safe transport for the diver to the nearest medical facility for immediate stabilization and assessment first. Then call the DAN Emergency Hotline for consultation with the local medical provider.

Even if symptoms were not severe and they resolved completely, a diver who has had multiple bouts of DCS must take special considerations. Especially if DCS is recurring following otherwise safe dive profiles, a dive medical specialist must be consulted to determine if diving can be resumed safely.


Next: Chapter 5 – Factors Contributing to Decompression Stress >