Diving and hyperbaric medicine
With thanks to A/Prof Michael Bennett, Clinical Associate Professor in the University of New South Wales and Senior Staff Specialist, Department of Diving and Hyperbaric Medicine, Prince of Wales Hospital
Hyperbaric medicine involves the treatment of disease by the administration of breathing gases (nearly always 100% oxygen) at pressures greater than one atmosphere absolute (ATA). The treatment process is commonly known as ‘ hyperbaric oxygen therapy’ or ‘HBOT’, and requires a pressure chamber and a means of delivering 100% oxygen. Operation is performed to a predetermined schedule by trained personnel who monitor the patient and may adjust the schedule as required. The most common treatment schedules in Australia are conducted between 2 to 2.4 ATA for 90 to 120 minutes, and many conditions require 20 to 30 such treatments.
One special kind of hyperbaric treatment is for divers with decompression illness (the bends). Divers are usually treated at higher pressures (2.8 to 4 ATA) and may breathe mixtures of helium and oxygen. Divers were the original reason that therapeutic hyperbaric chambers were developed, with the treatment of various other conditions growing popularity from about the early 1960s.
As with any area of medicine, evidence is constantly evolving and we present here a number of links which may help aid your understanding of HBOT.
Decompression Illness (DCI)
(Also called decompression sickness (DCS), or the bends)
DCI is a medical emergency until a person knowledgeable in diving medicine has been consulted.
DCI is a very diverse medical condition, and may present with mild symptoms several hours after leaving the water, or develop very acutely within minutes of surfacing and rapidly evolve to unconsciousness and death at the scene. The ultimate fate of the diver may be unclear early in the disease course, and in general all divers where DCI is thought the most likely diagnosis are recompressed in the chamber.
DCI may be due to:
1. Pulmonary barotrauma with ingress of air into the arterial circulation and subsequent cerebral arterial gas embolism (CAGE).
2. The development of bubbles in the tissues secondary to inadequate decompression time during the ascent from the deepest part of the dive. Bubbles arising in the tissues are called ‘autocthonous bubbles’. Bubbles in the venous blood in the 30 minutes to an hour after diving are very common and readily observed on cardiac echo. They are usually filtered in the pulmonary circulation and cause no problem.
3. Arterialization of venous bubbles through a persistent foramen ovale (PFO), ASD or pulmonary AV fistula.
The actual mechanism is unimportant in the acute phase of the illness because it does not influence resuscitation or treatment.
When to call, who to refer?
Any individual presenting to the ED with symptoms not readily explained by another mechanism, and who has undertaken compressed air breathing underwater within the last 24 hours should be assumed to have DCI until an expert has been consulted.
Who and how to call within NSW?
In NSW, during office hours call the Prince of Wales Diving and Hyperbaric Medicine Unit on 02 9382 3880. There is a similar unit available in each state and the NT. In NSW a specialist in diving medicine is available at all times through the Prince of Wales Hospital on 02 9382 2222, and there is a also a dedicated ‘Divers Emergency Service’ telephone where anyone can call to get advice from a diving doctor - 1800 088 200.
1. Until advised otherwise, all divers in the ED should receive oxygen at high flow via a non-rebreather mask.
2. All divers will have a degree of dehydration because of physiological changes on immersion. Fluids should be encouraged orally if the diver is not obtunded and more than four hours have elapsed since leaving the water. More acute patients, and those severely affected, should have liberal IV fluids (crystalloid balanced solutions such as plasmalyte or Hartmann’s are preferred).
3. Patients presenting acutely should be managed lying flat (supine or lateral as appropriate) to minimize further distribution of arterial bubbles to the cerebral circulation.
4. If advice on transfer is requested, in general we aim to minimize altitude exposure and sitting or standing. The choice of transport platform can be difficult.
Indications for Hyperbaric Treatment
There are many common uses for hyperbaric treatment other than decompression illness. The Undersea and Hyperbaric Medical Society presents a list of commonly accepted indications for HBOT and a link to a clear summary on each one.