If a diver surfaces and reports any signs or symptoms of decompression illness (DCI), they should immediately be evaluated against the list of DCI symptoms and equipped for re-entry into the water as quickly as possible.
Be certain that the victim is functionally responsive, mentally aware, and capable of answering questions such as “What day is it?”; “How old are you?”; “Where are you?”; etc.
Do not delay re-entry to the water but examine their dive computer for its last dive profile and see if any required decompression was omitted. Also note the maximum depth and total run time of the dive.
Whatever the breathing mix (nitrox or air) do not worry about calculating OTU or CNS oxygen exposure. OTU loading will be incidental and CNS O2 exposure will be in the range of 20% at most. The immediate priority is return to depth to compress inert gas bubble development and aggregation.
The following should be kept ready for usage and readily available on the dive deck so that there’s an immediate response to a DCI event.
- Two oxygen-clean scuba cylinders filled with 100% oxygen… pressure may be limited to approximately 2000psi (133 bar) due to storage pressure in H tanks.
- Two oxygen clean regulators with submersible pressure gauges. No extra second stages or low-pressure inflator hose should be attached.
- A ½-inch or 5/8-inch (15mm) line at least 80 feet (25m) in length should be deployed with approximately 40-50 pounds (20kg) of weight attached to the bottom to hold the line steady and vertical in the water column.
- Ideally, the line should be deployed from the main vessel’s amidships boarding area or stern platform and extended so the bottom of the line is as close to an exact depth of 60 feet (20m) as possible. The extra line length can be coiled on the deck and the line made fast to a cleat or other fixed point.
The symptomatic diver should enter the water as quickly as possible accompanied by another diver as tender. Descent should be made on the oxygen cylinder and breathing 100% oxygen. (Diver should wear a wet suit due to the prolonged period underwater.)
A slate and writing marker should be with the tending diver to communicate with the patient.
Another dive tender should accompany the two divers with a scuba cylinder filled with normoxic (standard) air at 21% oxygen. This will be used by the patient to breathe from during air breaks from the oxygen treatment. It can be worn by another diver with an extra long hose second stage to share with the patient. Do not burden the patient by having to change cylinders. Change the patient’s oxygen cylinder mounted to his BCD as necessary but ideally during the air breaks so no unnecessary interruption of oxygen breathing is done.
A clip or carabineer is helpful with corresponding eyes configured in the vertical line so that the patient can simply clip in and relax hanging motionless during the treatment. The clip can be on the diver’s BCD or other harness.
While there are several tables that have been in use for in-water recompression treatments, a standard Table 5 is effective and relatively easy to conduct.
Descend to a depth of 60 feet (18m) as quickly as comfortable for the patient to equalize ear pressure. Depth should be measured at the center of the diver’s chest.
Upon arrival at 60 feet (18m), the patient should breathe 100% for a 20-minute period. It is likely that most symptoms will resolve during the initial 20-minute breathing period at 60 feet (18m). A PO2 of 2.8 ATA will exist at 60 feet. (18m).
After 20 minutes on oxygen, the patient should switch to compressed air for a five-minute breathing period.
Repeat another 20-minute oxygen breathing period followed by a five-minute air break.
At all times, the patient should remain at rest with no physical exertion.
At the conclusion of the second 20-minute oxygen breathing period and the five-minute air break, begin ascent from 60 feet (18m) to 33 feet (10m) at a rate of one foot (30cm) per minute while breathing oxygen.
Upon arrival at a depth of 33 feet (10m), have the patient do a five-minute air break.
Then begin another 20-minute oxygen breathing period followed by another five-minute air break. PO2 at 30 feet will be nearly 2.0 ATA. (PO2 at 10m/33 feet is 2 bar)
Now the ascent to the surface will begin while oxygen breathing. Ascent rate will be one foot per minute. This will take 30 minutes.
It is now time to remove the patient from the ocean. Remove all equipment except the thermal suit so the patient is not physically stressed.
Upon surfacing, have the patient drink as much water as they are comfortable with. Inquire about any remaining symptoms. Let the patient take a fresh water shower, towel off, dress in comfortable shorts or lightweight cotton pants with a tee shirt or sweat shirt.
Take them to a well-ventilated (preferably air conditioned) cabin located in an area of the vessel with as little motion as possible to minimize any seasickness. They should lay flat on their back with their head on a pillow and be comfortable.
Have the patient begin breathing 100% oxygen via oral-nasal demand mask. Continue for two hours. Patient may drink water as needed.
Following two hours, do another field examination for CNS or pain DCI symptoms. It is likely that all symptoms will have completely resolved during the in-water phase of treatment.
Continue to have the patient breathe oxygen via demand mask for 24 hours with breaks as needed for hydration and bathroom relief.
Following the 24-hour surface oxygen breathing period, the patient may resume normal activity but with no physical exertion. Diving should be suspended completely.
Notes: Although unlikely, there is the possibility of a CNS oxygen reaction during the oxygen treatment breathing period underwater. If any symptoms are observed, the patient should immediately be placed on compressed air breathing for ten minutes before resuming the prescribed oxygen/air breathing protocol. While not an absolute requirement, having a full-face mask for the patient during O2 breathing would be desirable since any possible contingency reactions from oxygen toxicity would be minimized and lessen the possibility of losing the breathing source from a standard scuba second stage.
Tending divers should breathe a nitrox mixture of 40% oxygen. They will not need air breaks. Tenders may be rotated during the treatment.
Patients may exhibit anxiety and stress during the treatment. Every effort should be made to keep them calm and relaxed. It is also likely that treatment will continue after sunset and in darkness. Have lights available underwater and have a tender observe for any marine life threats.
If the vessel anchorage or mooring site is not calm, conduct the recompression in a protected lee area near an island, if available. Ideally, the motion in the vertical water column should be an absolute minimum.
Time is of the essence from the initial reporting or symptoms to re-entry to the ocean and return to a depth of 60 feet (18m). Most patients will resolve completely if treated within 30 minutes to one hour.
Time of treatment on Table 5 is two hours and fifteen minutes underwater. If deemed necessary, extra 20-minute O2 breathing periods can be added at either 60 or 33-feet (18m – 10m) depths but this should not be required. However, if any doubts exist about resolution of symptoms add the O2 extensions. As long as the supply of O2 is available, it can’t hurt and serves as an additional outgassing gradient for elimination of inert gas bubbles especially in areas of aggregation.
About Bret Gilliam. A licensed U.S. Merchant Marine Master, Gilliam has run hyperbaric treatment facilities and recompression chambers since 1971. He is credentialed as a Recompression Chamber Supervisor through NOAA, UHMS, ISAM, SPUMS, IBUM, and ERDI. His papers and articles on emergency diving treatment have been published by these groups as well as the American Academy of Underwater Science, the Divers Alert Network, and in the international press. He has presented his formal work at a variety of conferences and symposia since 1972.