DIVELOG JUNE 406

CPR IN DIVING ACCIDENTS:

Diving Medicine

Just the C or the PR too?

Professor Simon Mitchell, University of Auckland

I n the modern setting it is rare to hear a discussion of cardiopulmonary resuscitation (CPR) without someone mentioning the issue of “compression only CPR” (chest compressions without expired air resuscitation). Since resuscitation of injured divers is an unpleasant possibility that we all must confront, the subject of compression only CPR is sometimes raised in the context of diving (several times recently in on-line diving forums). There are substantial misunderstandings about this issue in the diving community, and it is a subject worthy of clarification in the pages of Dive New Zealand.

First, a little non-diving background. Traditional CPR, as most people will know, involves taking an airway – breathing – circulation (ABC) approach to resuscitation of a person who collapses and becomes unresponsive. In this paradigm, a person who collapses will have their responsiveness challenged by some sort of stimulation, and if apparently unconscious, their airway will be opened by the first responder. If there is no breathing the rescuer will then deliver expired air resuscitation (EAR) typically using a mouth to mouth technique. This is followed by a check for a pulse, and if there is no obvious pulse, chest compressions will be undertaken to establish circulation. The subsequent ratio of breaths to compressions has typically been considered dependent on whether there are one or two rescuers, but these details are irrelevant to this discussion. Early this decade a series of studies was published in the medical science literature that appeared to demonstrate that CPR in which the rescuers performed chest compressions only resulted in superior outcomes to CPR where the rescuers tried to perform both compressions and breaths. The results of 3 studies were analysed together. In these studies, subjects suffering cardiac arrest were randomly assigned to receive compression-only CPR or conventional CPR (compressions plus breaths) by an emergency dispatcher who instructed untrained first responders (by phone) in undertaking the assigned technique. This analysis showed a small but significant increase in survival (absolute increase 2.4%, number needed to treat = 41) when compression only CPR was used. The

latter means that one extra victim survived for every 41 victims managed with compression only CPR. These studies excluded cases in which there was intervention by bystanders trained in CPR, and consequently, they have been criticised as simply demonstrating that it is easier to instruct untrained laypeople in chest compressions alone than in compressions plus breaths via the telephone in an emergency. It was a controversial finding, but there is some plausibility. To be clear, these studies took place in the community where the the victim collapsed and stopped breathing because of a problem with their heart (a “community cardiac arrest”). Such events are typically caused by blockage of one of the arteries supplying blood to the heart (“a heart attack”) or by a disturbance of the heart rhythm due to some other cause. The crucial point to emphasise is that in such situations, at around the time the heart stops, there is a “normal” level of oxygen in the lungs because the victim was breathing normally right up to that point. Performing chest compressions circulates blood through the lungs, collecting some of that oxygen and carrying it to the vital organs like the brain. Although oxygenation is not optimal and will quickly become progressively less so, the study outcomes suggested that it was sufficient to “tide the patient over” until more expert medical care arrived. In addition to the fact that it appeared to work, compression only CPR had a number of other advantages. First it overcame the reluctance that bystanders often have in undertaking a complex process under pressure. If all they have to do is chest

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DIVE LOG Australasia #406 - June ‘24

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