Decompression sickness (DCS) is a rare and unpredictable injury that usually occurs far away from hospitals and hyperbaric treatment facilities. Thus, first aid measures that may be administered immediately after symptom onset are very important for the treatment of DCS. One such measure is first aid oxygen (FAO2), which replaces breathing air at surface level with oxygen delivered at the highest fraction possible. Oxygen breathing speeds up the elimination of inert gas from the tissues. This can produce symptom relief and, sometimes, complete resolution of symptoms. The benefits are intuitively clear and despite scarce data and lack of complete understanding of the possible mechanisms involved, FAO2 has been generally accepted in the diving community as a standard measure of first aid.
Divers often call the DAN Medical Information Line with questions concerning safety, efficacy, mode of oxygen administration and what to do after initiating FAO2.
Most of the answers to these questions are straightforward:
- Divers who breathe pure oxygen at the surface are not at risk of oxygen toxicity.
- Breathing pure oxygen at the surface may alleviate or even resolve symptoms of DCS.
- Pure oxygen is beneficial first aid in decompression illness (DCI), which encompasses both arterial gas embolism (AGE) and DCS.
- The most efficient mode of FAO2 administration is that which provides the highest percentage of oxygen for the longest time. A demand regulator can provide a very high fraction and is appropriate for spontaneously breathing patients. If the oxygen supply is limited, closed-circuit breathing (via a rebreather device) will extend the supply duration.
The controversial questions are:
- How long should oxygen be administered?
- What to do with divers if their symptoms resolve before starting evacuation or reaching a recompression chamber?
The initial duration of FAO2 therapy often depends on the available supply. Thirty minutes might be considered a desirable minimum duration. In some cases, symptoms resolve soon after the start of FAO2 and may return subsequent to cessation of oxygen therapy. Even after treatment in recompression chambers, symptoms may recur in 15 to 40 percent of cases. Thus, to make FAO2 more efficient, it should be used more aggressively. For example, if a diver presents with neurological symptoms, the duration of FAO2 should last at least 90 minutes, even if the symptoms resolve after the first few minutes of breathing oxygen.
The next question is what to do in case symptoms disappear completely before the diver reaches a hyperbaric facility. A complete resolution of DCS symptoms may occur spontaneously or as a response to FAO2. Historical data indicate a substantial percentage of spontaneous recovery even among severe cases of DCS. Complete relief occurs in 15 to 25 percent of divers admitted to recompression chambers after receiving FAO2. This does not help in real time since the outcome of a given case cannot be predicted at the outset of the event. The relief rate could be underestimated if some divers choose not to be medically evaluated after the self-administration of oxygen. This is certainly not encouraged. Even after apparently complete resolution with FAO2, divers should be evaluated by a medical professional to ensure that subtle effects do not remain. In many cases, even after spontaneous or oxygen-facilitated improvement, patients will be recompressed using a therapeutic treatment table to help ensure the best outcome.
When responsible for a group of divers in remote locations, dive operators face additional challenges. They may be pressured not to administer FAO2 if this action serves as a trigger to interrupt the trip and start the evacuation of an injured diver, regardless of the outcome following first aid. This is troubling since FAO2 will likely be most effective if started immediately after symptom onset. Unfortunately, early-stage symptoms may be similar to those caused by nondiving or unrelated conditions. Rather than triggering an irreversible course of action, it should be accepted that early FAO2 administration is beneficial, but that it may also be given in cases not requiring evacuation.
Despite this acceptance, whether FAO2 may be considered a definitive treatment in some cases and under certain conditions remains a controversial issue. We have asked experts in the field to provide their thoughts.
Can FAO2 be considered a definitive treatment in some conditions?
James Francis: FAO2 should not be considered to be a definitive treatment for DCI. By definition it is holding management, along with adequate rehydration, until definitive treatment (hyperbaric oxygen) can be administered. In saying this, there are a number of points that need to be made
- DCI can be a difficult diagnosis, even for experienced diving doctors. There are numerous diving-related and nondiving-related conditions that can mimic DCI. Most dive groups have no medically trained members amongst them, and, consequently, telephone advice should be sought. Since the expert on the other end of the line is wholly dependent on the quality of the history and examination elicited by those who are tending to the casualty, it is frequently the case that a presumptive diagnosis is the best that can be achieved. As such, there are casualties who are evacuated with a diagnosis of DCI who may be suffering from something else.
- Regardless, it is important that arrangements are made, as a matter of urgency, for the evacuation of the casualty to the closest center appropriately staffed and properly equipped to assess and manage the casualty.
- Prior to and during evacuation, FAO2 is invaluable because it accelerates the elimination of inert gas and therefore addresses the main problem in DCS. Even if the diagnosis turns out not to be DCI, FAO2 will do no harm to people who were fit to dive prior to the accident. Thus, it provides a potential benefit with no downside.
- If the casualty’s symptoms and/or signs resolve prior to their arrival at the chosen medical facility, it may be the case that no hyperbaric treatment is required. This could be because the diagnosis turns out to be a condition other than DCI, or the casualty had DCI and it has taken several days for him or her to be evacuated. If the casualty only ever experienced mild symptoms it may be the case, after a full examination, that no further treatment is required. In this situation, it may appear that FAO2 was a definitive treatment, but it is not an outcome that can or should be anticipated.
Michael Bennett: I entirely agree that FAO2 is not a definitive therapy for serious DCS. Any case in which there is a reasonable suspicion of serious DCS, the casualty should receive FAO2 and be evacuated for definitive treatment. The partial or complete resolution of symptoms during FAO2 would not influence this decision. A responsible person who allowed suspicious symptoms to remain untreated for fear of precipitating a disruptive or unnecessary evacuation would be doing the diver a great disservice, and this course of action should be actively discouraged.
Having made that clear, we still have two questions to answer. Is FAO2 a suitable definitive therapy for any suspected case of DCS, and are there other conditions that may present after diving and can be treated with FAO2 alone? The second is more easily addressed. There are many self-limiting or nonthreatening injuries and maladies that may present following diving. Examples include headache due to carbon dioxide retention (skip breathing) or dehydration, earache or sinus pain following milder degrees of barotraumas, overexertion, numbness or tingling from a tight wetsuit and indigestion. There are many others, and determining which is causing the symptoms may be a very difficult task. Some of these ailments will respond to the application of FAO2 , and many will appear to do so as they improve over time. None are likely to require evacuation, and none require recompression.
If there is some suspicion by those present that DCS may be the culprit, it is recommended that divers be given FAO2 while expert opinion is sought. Despite the notorious difficulty in eliminating the diagnosis of DCS, experienced diving doctors can often clearly identify factors that make DCS very unlikely. Under those circumstances, such an experienced physician may be comfortable prescribing simple measures with or without further oxygen. It is highly unlikely that such divers will need evacuation. Under these circumstances, FAO2 could be considered definitive treatment for some conditions.
Can FAO2 ever be considered definitive therapy for suspected DCS? While the answer might still be regarded as controversial by some diving doctors, I believe there are circumstances where the answer to this question is also yes. This question was considered in great detail at a 2004 workshop in Sydney, Australia, on the treatment of mild decompression illness in remote locations. The experts present agreed on a number of consensus statements including the following:
Consensus Statement 4: Some patients with mild symptoms and signs after diving can be treated adequately without recompression. For those with DCI, recovery may be slower in the absence of recompression.
Consensus Statement 5: Some divers with mild symptoms or signs after diving may be evacuated by commercial airliner to obtain treatment after a surface interval of at least 24 hours, and this is unlikely to be associated with worsening of outcome.
The workshop went into considerable detail to define what is meant by “mild symptoms and signs,” in particular noting that any complaints must be static or remitting and that neurological signs need to have been excluded by medical examination. The bottom line is that in carefully defined situations, usually with the benefit of expert opinion, FAO2 may be adequate therapy in order to avoid a lengthy and expensive evacuation for the purpose of recompression.
*Consensus statements excerpted from: Mitchell SJ, Doolette D, Wachholz CJ, Vann RD, eds. Management of mild or marginal decompression illness in remote locations: workshop proceedings. Durham, N.C.: Divers Alert Network, 2005.
Meet the Experts
Michael Bennett, M.D., FANZCA, ANZCA Cert DHM, is a senior staff specialist at the Prince of Wales Hospital and tenured associate professor of hyperbaric medicine at the University of New South Wales in Sydney, Australia. He has 17 years of experience with the management of remote diving injuries in the South Pacific and received his doctorate for work on the evidence-basis of diving and hyperbaric medicine.
James Francis, B.Sc., MBBS, M.Sc., Ph.D., DipDHM, MFOM, has been a specialist in diving medicine for 26 years. He learned his trade while serving in the British Royal Navy in which he was the head of undersea medicine before leaving when the service downsized in the mid ’90s. Since then he has worked for the U.S. Navy as a civilian consultant and now teaches diving medicine and serves as an expert witness in diving medicolegal cases.
Administering Oxygen First Aid*
Follow these simple steps to provide oxygen to a breathing injured diver with a demand inhalator valve. This is the preferred method of providing emergency oxygen. It is intended for use by divers who are conscious and breathing normally. For divers who are unconscious or not breathing well enough to activate the demand inhalator valve, use a nonrebreather mask or add supplemental oxygen to CPR.
- Make sure the scene is safe for you to enter and obtain first aid equipment, and don exposure protection like gloves and masks or face shields as appropriate.
- Ensure airway and breathing.
- Inform the injured diver that oxygen first aid may help.
- Deploy the oxygen unit.
- Take a breath from the demand inhalator valve and exhale away from it.
- Place the mask over the injured diver’s mouth and nose.
- Monitor the injured diver and the oxygen pressure gauge.
- Call EMS or other appropriate medical facility.
- Contact DAN for consultation and coordination of hyperbaric treatment, if necessary.
Prior to any dive outing, ensure:
- you have enough oxygen to last from the dive site to emergency medical care
- the oxygen equipment is assembled and ready to use
- all masks are clean and free from signs of age or wear
- someone in the group is trained in oxygen administration and conducting an on-site neurological assessment
If diving with a dive charter company or dive center:
- confirm the dive center has oxygen available at the dive site or on the boat.
- ask about staff training for oxygen, neurological assessments and its use.
- ask to see the equipment to make sure it is all in good working order.
For more information on the signs and symptoms of decompression illness or to receive training in DAN’s Oxygen First Aid for Scuba Diving Injuries course, contact your local dive center or visit DAN.org to find the nearest DAN Instructor.
*Excerpted from the DAN Oxygen First Aid for Scuba Diving Injuries Student Handbook
© Alert Diver — Q4 Fall 2010