DIVELOG JUNE 406

compressions, without having to remember the ratio of breaths to compressions, and different rates in one- or two-person CPR etc, then they are likely to experience less anxiety about starting CPR when it was needed. Similarly, compression only CPR mitigated concerns that first responders might have about communicable disease transmission if performing mouth to mouth EAR. Thus, compression only CPR offered the prospect of seeing many more victims of cardiac arrest in the community receive supportive care in a timely fashion. For all these reasons the technique has been widely promoted as a legitimate (and perhaps preferable) strategy in cardiac arrest, especially for responders with no training in proper CPR. Unfortunately the advice is frequently not contextualised accurately enough. Compression only CPR works in community cardiac arrest because the cardiac arrest is due to a heart problem, and there is at least some oxygen in the lungs at the time. In contrast, in drowning the patient becomes hypoxic before the cardiac arrest; indeed, hypoxia is the eventual reason the heart stops. That is, as hypoxia worsens, breathing efforts cease and eventually, if the hypoxia is not corrected, there will also be a cardiac arrest. Compression only CPR will not work in this setting because there is effectively no oxygen to circulate. It is more complicated than that though. As implied above, in

drowning there is a period between respiratory and cardiac arrest. If hypoxia can be corrected during this period then cardiac arrest may be prevented which, in reality, is the only thing likely to save a life out in the ocean. In a diving rescue it is not possible to tell if the victim is in respiratory but not cardiac arrest, but if that is the situation (and we would hope it is), then the only realistic chance of saving the victim is to stop them going into cardiac arrest in the first place. Thus, rescue breaths (breaths as early as it is physically possible to administer them) may be the key life-saving intervention in drowning. Finally, one of the reasons that compression only CPR works in community cardiac arrest is that definitive emergency care frequently reaches the patient quickly. If paramedics can take over early in the event and restore oxygenation of the lungs, then compression only CPR may be enough to get by in the interim. However, it is likely to take longer to obtain expert support in typical diving situations, so compression only CPR is much less likely to be adequate. In conclusion, compression only CPR is not appropriate for use in cardiac arrest where drowning may be the cause (as it is in most diving related deaths). There is no substitute in diving for getting properly trained in CPR and practicing the technique regularly. Hopefully you may never need it, but if you do you may save a life.

Professor Simon Mitchell MB ChB, PhD, DipOccMed, DipAdvDHM (ANZCA), FUHM, FANZCA Simon works as an anaesthesiologist at Auckland City Hospital and is Professor of Anaesthesiology at the University of Auckland. He provides on-call cover for the diving emergency service in New Zealand. He is widely published with two books and over 160 scientific journal papers or book chapters. He co-authored the hyperbaric and diving medicine chapter for the last four editions of Harrison’s Principles of Internal Medicine. He has been Editor-in-Chief of Diving and Hyperbaric Medicine Journal since 2019. He has twice been Vice President of the UHMS and in 2010 received the society’s Behnke Award for contributions to the science of diving. Simon has a long career in sport, scientific, commercial, and military diving. He was first to dive and identify three historically significant deep shipwrecks in Australia and New Zealand, including one in 2002 which was the deepest wreck dive undertaken at the time. He was conferred Fellowship of the Explorers’ Club of New York in 2006, and was the Rolex Diver of the Year in 2015. His most recent expeditions were the Pearse Resurgence cave exploration (New Zealand) in 2020, a project to take arterial blood gas specimens from an elite freediver at 60m 2021, and hunted for a shipwreck in the sub Antarctic in 2022.

References: 1. Soar J, Perkins GD, Abbas G et al. European Resuscitation Council Guidelines for Resuscitation 2010 Section 8. Cardiac arrest in special circumstances: Electrolyte abnormalities, drowning, accidental hypothermia, hyperthermia, asthma, anaphylaxis, cardiac surgery, trauma, pregnancy, electrocution. Resuscitation 2010; 81: 1400-1433

2. Mitchell SJ, Bennett MH, Bird N et al. Recommendations for rescue of a submerged unconscious compressed gas diver. Undersea Hyperbaric Med 39, 1099-1108, 2012

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DIVE LOG Australasia #406 - June ‘24