The advantages of oxygen over air tables include increasing nitrogen elimination gradients, avoiding extra nitrogen loads, increasing oxygenation to tissues, decreasing the depths required for the reduced exposure time and improving overall therapeutic efficiency. The same caveats about organization, resources and sea conditions are applicable when comparing underwater air and underwater oxygen treatment.
Minimum requirements for the safe conduct of in-water oxygen tables
- At least one G-sized (7000 litres) oxygen cylinder – medical grade.
- Regulator and hoses (minimum 12 metres – marked in 1-metre intervals) rated as ‘oxygen-safe’ and maintained appropriately.
- Full-face mask.
- Suitable method for weighting diver and attendant to avoid unwanted changes in depth.
- Hookah air supply for attendant diver.
- Suitable diving platform (boat or wharf) above column of water to >9-metre depth.
- Appropriate thermal protection for prolonged immersion.
- A suitable communication system with divers.
- Appropriately trained individuals to oversee the procedures.
- Attendant diver (breathing air).
- Suitably trained attendant(s) to ensure appropriate decompression rate and gas supply.
- Ability of the patient diver to be safely immersed for the duration of the table (e.g. not having seizures or unconscious).
- Protected site with calm water.
- Freedom from unacceptable tidal fluctuation and current.
- Water temperature compatible with thermal protection available.
Beginning in 1970, this option has been applied to the underwater treatment of DCS. The procedures were developed in response to an urgent need for management of cases in remote localities – remote in both time and distance from hyperbaric facilities. As a result of the success of this treatment, and its ready availability, it is now practised even when experts are not available to supervise it.
The physiological principles on which this treatment is based are well known and not contentious, although the indications for treatment have caused some confusion. As for conventional oxygen therapy tables, underwater oxygen was first applied mainly for minor cases of DCS, but it was subsequently found to be of considerable value in serious cases.
The techniques and equipment for underwater oxygen therapy are designed to make for safety, ease and ready availability, even in medically unsophisticated countries. Although accurate estimates are problematic, it is likely this approach is now in widespread use in the Pacific Islands and remote parts of Australia.
Hawaiians have included a deep air ‘dip’ before underwater oxygen treatment, in an attempt to force bubbles back into solution or to allow bubbles trapped in arteries to transfer to the venous system.
Oxygen is supplied at maximum depth of 9 metres from a surface supply. Ascent is commenced after 30 minutes in mild cases, or 60 minutes in severe cases, if significant improvement has occurred. These times may be extended for another 30 minutes if there has been no improvement. The ascent is at the rate of 12 minutes/metre. After surfacing, the patient should be given periods of oxygen breathing, interspersed with air breathing, usually on a 1 hour on, 1 hour off basis, with respiratory volume measurements and chest x-ray examination if possible.
No equipment should be used with oxygen unless it is assessed ‘oxygen safe’ or if it is contaminated, dirty or lubricated with oil.
An air breathing diver attendant should always be present, and the ascent should be controlled by the surface tenders. The duration of the three tables is 2 hours 6 minutes, 2 hours 36 minutes and 3 hours 6 minutes. The treatment can be repeated twice daily, if needed.
The underwater oxygen treatment table is not meant to replace formal recompression therapy in chambers. It is an emergency procedure, able to be applied with equipment usually found in remote localities, and is designed to reduce the many hazards associated with conventional underwater air treatments. The customary supportive and pharmacological adjuncts to the treatment of recompression sickness should still be used, if available, and the superiority of experienced personnel and comprehensive hyperbaric facilities is not being challenged. Underwater oxygen treatment is considered as a first aid regimen, not superior to portable RCCs, but sometimes surprisingly effective and rarely, if ever, detrimental.
The relative value of proposed first aid regimens (underwater oxygen, underwater heliox, an additional deep descent and surface oxygen treatment) needs to be clarified.
Use of Underwater Oxygen Treatment
Because this treatment is applied in remote localities, many cases are not well documented. Twenty-five cases were well supervised before this technique increased suddenly in popularity. Two such cases are described (Case Report 13.3 and Case Report 13.4).
CASE REPORT 13.3: A 68-year-old male salvage diver performed two dives to 30 metres for 20 minutes each, with a surface interval of 1.5 hours, while searching for the wreck of HMS Pandora about 100 miles from Thursday Island in the Torres Strait.
No decompression staging was possible, allegedly because of the increasing attentions of a tiger shark. A few minutes after surfacing, the diver developed paraesthesiae, back pain, progressively increasing incoordination and paresis of the lower limbs.
Two attempts at underwater air recompression were unsuccessful when the diving boat returned to its base moorings. The National Marine Operations Centre was contacted for assistance.
It was about 36 hours after the dive before the patient was flown to the regional hospital on Thursday Island.
Both the Air Force and the Navy had been involved in the organization, but because of very hazardous air and sea conditions, and very primitive airstrip facilities, another 12 hours would be required before the patient could have reached an established recompression centre (distance, 3000 km [2000 miles]).
On examination at Thursday Island, the patient was unable to walk, with evidence of both cerebral and spinal involvement. He had marked ataxia, slow and slurred speech, intention tremor, severe back pain, generalized weakness, difficulty in micturition, severe weakness of lower limbs with impaired sensation, increased tendon reflexes and equivocal plantar responses.
An underwater oxygen unit was available on Thursday Island for use by the pearl divers, and the patient was immersed to 8 metres of depth (the maximum depth off the wharf). Two hours were allowed at that lesser depth, and the patient was then decompressed. There was total remission of all symptoms and signs, except for small areas of hypoaesthesia on both legs.
CASE REPORT 13.4: A 23-year-old female sports diver was diving with a 2000-litre (72 cubic feet) scuba cylinder in the Solomon Islands (nearest recompression chamber was 3500 km away and prompt air transport was not available); the dive depth was 34 metres and the duration approximately 20 minutes, with 8 minutes of decompression. Within 15 minutes of surfacing, she developed respiratory distress, then numbness and paraesthesiae, very severe headaches, involuntary extensor spasms, clouding of consciousness, muscular pains and weakness, pains in both knees and abdominal cramps. The involuntary extensor spasms recurred every 10 minutes or so.
The patient was transferred to the hospital, where neurological DCS was diagnosed, and she was given oxygen via a facemask for 3 hours without significant change. During that time an underwater oxygen unit was prepared, and the patient was accompanied to a depth of 9 metres (30 feet) off the wharf. Within 15 minutes she was much improved, and after 1 hour she was asymptomatic. Decompression at 12 minutes/meter was uneventful, and a commercial aircraft subsequently flew the patient to Australia.
There have now been many hundreds of cases of underwater air and underwater oxygen treatments recorded12. Apart from the relative paucity of complications, the major lesson learned was that prompt re-immersion of the diver allowed shorter duration of treatment and complete resolution of DCS manifestations. Many divers so treated resumed diving within days.