Diving and Hyperbaric Medicine
As scuba divers, we all have a basic understanding of decompression illness, and recognise the safety precautions taken to decrease the possibility of dive-related maladies. We dive within our no-decompression limits, complete safety stops, and ensure we never hold our breath. But, have you ever found yourself wanting to know more? Deeper understanding cultivates a well-rounded diver. Therefore, in an effort to gain further insight into this fascinating field, we spoke to Dr David Wilkinson, the medical director of the Hyperbaric Medicine Unit at the Royal Adelaide Hospital.
What is DCI, and can you explain some of the most common signs and symptoms?
Decompression Illness (DCI) is a bubble-related injury – you will not have DCI without bubbles, but conversely, not all bubbles in the body produce DCI. Most of the time it will appear following SCUBA diving, but DCI can occur in other diverse situations (such as altitude or space and some medical procedures). DCI can present with a broad range of signs and symptoms, which can make clinical decisions difficult at times. However, most symptoms of DCI are relatively mild and feature constitutional symptoms (feeling unwell, not quite right, aching all over the body), altered sensations in the body (numbness, pins-and-needles or tingling in an arm, leg or some part of the body) and pain. Most people have probably heard of pain as a symptom of DCI but I always say the pain can be of any type – severe or mild, constant or intermittent. Certainly, severe pain does not guarantee DCI and mild pain does not exclude it. More serious presentations of DCI may involve loss of consciousness and spinal cord injury resulting in loss of movement of limbs. It must also be remembered that DCI is a rare event following diving, probably no more than a handful of cases per 10,000 dives. So it is important to keep this in perspective – I am a diver, knowing all of this doesn’t stop me diving.
What is the process if someone comes to the hospital with a suspected case of DCI?
If you think a diver has DCI, the first thing to do is get them resting or lying down, put them on oxygen if available and talk to someone about help. Call an ambulance if you are concerned, they always carry oxygen. On arrival at the hospital emergency department, the diver will be assessed by a doctor, put on oxygen if not already and usually an intravenous needle inserted for fluid administration. Diving specialists like me will be consulted to agree on a diagnosis. Signs and symptoms after diving may be due to other causes, but if we think it may be DCI we will plan to assemble our staff to put the diver in the hyperbaric chamber. The diver is accompanied by a trained nurse in the chamber. There are a number of different “recompression” tables we can use, but most commonly the diver is in the chamber for almost 5 hours breathing oxygen with intermittent air-breaks. The chamber is compressed to the equivalent of 18 metres seawater at maximum and slowly decompressed over time.
In layman’s terms, how does hyperbaric oxygen therapy work?
There are 3 ways by which recompression will treat a diver with DCI:
- Increased pressure to reduce bubble size
- Breathing oxygen to aid “off-gassing” of nitrogen
- The specific biological effects of HBOT
Divers learn about Boyle’s law – an increase in pressure will reduce the volume of a gas-filled space. When the diver is recompressed to 18 msw, any remaining bubbles will be reduced in size and can immediately improve symptoms. Most bubbles encountered in SCUBA divers come from their breathing gas which is usually air. The bubbles will reflect the gas composition of air – mostly nitrogen with around 20% oxygen. Breathing oxygen (which does not contain nitrogen) will aid the off-gassing of the nitrogen from the bubble more quickly. This is the argument for giving oxygen as a first aid to divers in the field – we encourage it. Doing it in the hyperbaric chamber under pressure accelerates this process.
Within the hyperbaric chamber, the use of 100% oxygen at pressures equivalent to diving to 18 msw has a whole range of biological effects. Not least of which is oxygen toxicity which may result in the diver losing consciousness or having an oxygen seizure. Divers are trained to avoid this degree of oxygen exposure in the open water, so such procedures should only be undertaken in an appropriate place such as a hospital with properly trained personnel. However, properly harnessed, the effects of HBOT can be very beneficial. Some of the manifestations of DCI in divers can be attributable to a pathological process of inflammation, initiated by the bubbles in the blood and tissues. Once initiated, this inflammatory process can continue throughout the body producing signs and symptoms of DCI. HBOT can very successfully turn off this inflammatory process, resolving signs and symptoms of DCI and preventing their recurrence in the early convalescent stage.
Once the DCI has resolved with recompression (which is a form of HBOT), the diver requires a period of recovery before considering a return to diving. This should be discussed with the treating diving doctor and considers many aspects of the dive and the diver.
Can hyperbaric oxygen therapy be used for non-diving related maladies?
Absolutely yes. As above, I’ve suggested that HBOT can have a number of biological effects. We are yet to understand a number of these in detail. However, we do have good clinical evidence for benefit for conditions such as non-healing ulcers and wounds, particularly in people with diabetes who are prone to complications such as amputation. Also for people who have had radiotherapy, HBOT may heal some of the radiation related injuries to normal tissues. HBOT can also help people with serious infections, such as the “flesh-eating bug” infection.
As we are in a hospital environment with well-trained personnel, we can confidently treat such medical patients with HBOT, despite this population being generally “unfit to dive” in the usual sense.
For you, what is the most fascinating part of hyperbaric medicine?
From the day I first saw that large rectangular hyperbaric chamber I was taken by the “frontier of medicine” that hyperbarics offered. I have been part of a marvellous journey in a little trodden field of medicine. I have travelled and talked to divers all around the world. I have treated patients who were thought to be dying or couldn’t be improved. Not everyone got better it is true, this is not a miracle cure. I have added to the research in understanding how HBOT works and have been part of a group of like-minded clinicians who have contributed to the field of Diving and Hyperbaric Medicine in this country. As I approach the end of my own career, these are the things that I am most proud of.
Thank you to Dr. David Wilkinson for speaking to us and sharing such thorough insight into the world of hyperbaric medicine. This is a captivating field of study, and we are grateful to have broadened our knowledge.