(decompression diver and trimix class)
Central Nervous System (CNS) oxygen toxicity at depth usually results in a diver’s death. CNS toxicity itself is not fatal. But the stricken diver dies as a result of either a massive over-expansion injury caused by floating to the surface while in spasm; or by drowning as a result of the diver spitting out the regulator or mouthpiece while in spasm and then inhaling water when the episode abates. Any diver may present a CNS-like episode without prior warning. Please bear in mind that almost any “informed” intervention on your part may increase the diver’s odds of surviving the episode.
If you and your buddies follow the established NOAA protocol for single dives and watch your 24-hour limits, it is highly unlikely you will ever see or suffer a CNS incident. However, as unlikely as it may be, you will be asked to demonstrate the following procedure during your TDI Techdivertraining program. This procedure is simply a suggestion of how to attempt to stabilize and surface with a diver who has presented the signs of a clonic / tonic episode. You may regard this as a basic solution and it is certainly open for further refinement.
1/ Stabilize the convulsing diver. Control his position in the water column by making physical contact (either with his person or a piece of equipment.)
2/ Do your best to hold the regulator in his mouth (certainly the gas he is breathing MAY be causing the convulsions; however, breathing any gas is better than breathing water).
3/ Signal to other team members that you need assistance
4/ Do not attempt to ascend until the diver’s body relaxes, the convulsions cease and the diver resumes breathing.
5/ When convulsions cease, check the level of diver’s consciousness. If they are awake, signal them to switch regulators to a gas YOU KNOW is appropriate for your current depth. If they are breathing but are unresponsive (likely) you may not be able to switch regulators. That’s OK. MAKE SURE THAT WHICHEVER REGULATOR THEY ARE BREATHING IS ATTACHED TO AN ABUNDANT GAS SUPPLY Monitor gas levels for the stricken diver often.
6/ Adopt recovery position** and begin ascent. Use the stricken diver’s buoyancy compensator to control ascent for you both. (Open the automatic vent on his dry suit and yours.) If you have another team member helping, sandwich the stricken diver between the two of you.
7/ If possible, blow a signal marker to tell your surface support that you have an in-water emergency.
8/ Complete your decompression schedule. You may choose to accelerate it if circumstances dictate, but DO NOT risk DCI to get the stricken diver to the surface… Remember, he has the same obligation as the rest of his team
9/ Be prepared for a second series of convulsions.
10/ Bring diver to surface and secure and remove gear (inflate wings, clip to equipment line, cut harness), get diver to surface personnel or on boat or on shore.
11/ Activate EMS. Note: The correct call to the Coast Guard in this situation would be a pan pan and NOT a mayday.
12/ Monitor. Document. Follow Instructions from EMS or Coast Guard. Reassure. Treat for Shock. Watch for signs of DCI. Set diver’s gear aside for inquiry… Either one among your team or group, or more formal.
* Oxygen Toxicity may present itself underwater in the form of a clonic-tonic convulsion. However, a convulsing diver may or may not be experiencing a CNS toxicity episode. You cannot diagnose precisely what’s going on, so always deal with the situation in a structured way and resist the temptation to second-guess the situation.
Do check to see if the MOD of the gas the stricken diver was breathing when they convulsed corresponds to the depth they were at. Do get them on a leaner mix or get them higher in the water column, as swiftly as is possible without compromising other safety protocols. Do Watch your own gas switches.
** Recovery position = Anything that works Essentially, you will ride the stricken diver through the water column making sure you have control of their BC, their airway (keep it open) and the regulator (in their mouth). I find it difficult to completely control venting gas in a stricken diver’s drysuit (and my own in these circumstances) if I maintain a horizontal trim. I find I do better if I present them and myself in a semi-vertical attitude. I also prefer to be able to monitor the diver’s eyes, and so prefer to be facing them rather than being behind them. Try threading your right arm under theirs. Keep the drysuit shoulder vent up and OPEN. Bring your hang around their shoulder and hold their BC inflator in your right hand. Use your left hand to hold their regulator in place. Do your best and remember that style takes a back seat to function… Use any fixed aid — such as an anchor line or wall — to assist and arrest your ascent. This is one of the few exercises on your training course where you are allowed to hold onto ascent lines and walls, and where you will not be penalized for being vertical in the water.
N.B. several texts suggest not to try to replace a regulator that has fallen out of a diver’s mouth. The rationale is that if the diver tries to breathe, there is a chance that some water may be present and cause laryngospasm. Not replacing a regulator may be the correct “action” if the diver is being recovered from a few metres his rescuer is making a direct ascent to the surface. However, if ascent is going to take several minutes, and a regulator is not replaced, the diver most certainly will breathe water and drown. Make your own decision…