An unremarkable dive at high altitude ended with a trip to the hyperbaric chamber
A 48-year-old woman was diving at an altitude of approximately 6000 feet (~1800 m) altitude. She was diving with her husband, breathing compressed air, in water at a temperature of approximately 90 degrees F (32 C). They dived to 64 ffw (20 mfw) for 40 minutes bottom time before ascending to 40 ffw (12 mfw) for a 5 minute safety stop. They then ascended to 20 ffw (6 mfw) for a 5 minute safety stop, then to 15 ffw (5m) for another 5 min safety stop. They were both using dive computers and neither of those alarmed or indicated omitted decompression at any time. No rapid ascent or unusual occurrences any time during the dive. Approximately 45 minutes after surfacing, the diver experienced numbness and tingling in her right foot which ascended to her right hip, resulting in weakness and numbness in her right leg. Her husband drove her to the Emergency Department (ED), where they arrived 1.5-2 hours after surfacing. In the ED she was placed on 100% oxygen via a Non-Return Face Mask. The decision was made to transfer the patient for hyperbaric oxygen recompression therapy and she was transported directly to the hyperbaric medicine chamber. Later, she was still on 100% oxygen and stated that her symptoms had almost completely resolved.
Diving at altitude is exciting and a challenge many divers enjoy. At high elevations above sea level the ambient air pressure upon a lake is less than one atmosphere. The means the pressure differences when a diver ascends are greater than if a diver were to make the same ascent from the same depth in the sea. Accordingly, altitude diving requires specialist training, excellent buoyancy control and adjustments to the No Decompression Limit for any particular depth. Many dive computers automatically adjust for lower ambient pressure experienced at high altitude but not all do, so it pays to check the user manual when planning a dive in a mountain lake. Even if no mishaps occur and no warnings are given by a diver's personal dive computer, high altitude divers should employ additional conservative measures such as maintain normal hydration, use nitrox whenever possible, avoiding or reducing repetitive diving, using an ascent line to slowly ascend hand-over-hand, and avoid or reduce strenuous work both in the water and after the dive.
When diving at altitude it is also prudent to have adequate oxygen on hand to last the journey to the nearest Emergency Department, in this case 1.5-2 hours away.
~ Peter Buzzacott, MPH, PhD
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