Reported StoryAn experienced 35-year-old rebreather diver (400 dives on a closed-circuit rebreather) did a single dive off a boat to 164 feet (50 meters) using trimix 18/25 (18% oxygen, 25% helium, balance nitrogen) for 50 minutes total dive time. (See the profile in Figure 1.)
The water temperature was 50-59°F (10-15°C), visibility less than 10 feet (3 meters). The oxygen partial pressure in rebreather was set to 1.2 and varied between 1 to 1.2 ATA. The same diluent gas and PO2 settings were used throughout the dive. His longtime dive buddy, a physician, accompanied him; they stayed close together during the dive.
Soon after the dive when back on the boat, the diver complained of pain in his right shoulder with a severity of 2-3 on the scale of 0 to 5. He started breathing oxygen at surface pressure (normobaric) using a demand regulator on his oxygen S40 tank. During the first 10 minutes his pain grew worse before it started subsiding. After 20 minutes he was pain free.
He continued breathing oxygen for another 20 minutes (40 minutes total). Symptoms did not return after he stopped breathing oxygen. The diver refused the offer to contact DAN even though he had a DAN dive accident insurance policy. His buddy, who reported this incident, checked with him two days later and confirmed that pain did not return.
CommentsThe two divers had a similar dive profile, using a reputable dive computer and staying within the ceiling all the time. Despite that, one diver got decompression sickness (DCS), and the other had no symptoms. (The ceiling is marked in red in Figure 1; this indicates the shallowest depth to which diver may ascend — i.e., the next decompression stop depth after decompression at given stop.)
Joint and muscle pain caused by DCS is more likely at greater depths, but factors other than overall depth and time profile may contribute to Type 1 DCS. In this case, the diver was not aware of any additional affliction that may have enhanced his shoulder DCS.
Breathing oxygen at surface pressure is the best first aid. Technical divers usually have plenty of oxygen available as well as a demand regulator cleaned for oxygen use. Recreational divers depend on a first aid kit that includes a dedicated regulator with a mask and a limited oxygen supply. The case-management scenario reported here is probably quite common among technical divers, thus postdive joint pain (Type 1 DCS) is probably under-reported.
Note that the pain may get worse for a while before it gets better while administering surface oxygen. The diver should be aware of this and not end first aid too soon. It is sometimes reported that the failure of surface oxygen first aid in Type 1 DCS may be due to giving up too early. However, some cases may be resistant to first aid alone and may require additional treatment. All cases of DCS, even if resolved spontaneously or on surface oxygen, should be evaluated by physician.
— Dr. Petar J. Denoble