From a French OHCA prospective cohort, we evaluated the impact of bystander-initiated CO-CPR on the neurological outcome. We did not observe significant differences in neurological outcomes according to the CPR method performed (S-CPR or CO-CPR), whatever the cause of OHCA (asphyxial or non-asphyxial). These results are consistent with the observations of SOS-KANTO and Rea et al., who did not find differences between CO-CPR and S-CPR in medical OHCAs.2,7 Similar results were reported by Panchal et al. in OHCA secondary to non-cardiac causes.13 In contrast, Ogawa et al. found that S-CPR was beneficial in OHCA secondary to non-cardiac causes, but not in OHCA secondary to cardiac causes.12 Several studies have reported better neurological outcome in subjects who received bystander-initiated CO-CPR when the etiology of OHCA was a cardiac cause.2,7,11,14 Kitamura et al. in a large population showed that CO-CPR was beneficial for medical OHCA (excluding some causes: asphyxia, electrocution, drowning and drug overdose) after one-to-one propensity score matching.16 However, they were unable to adjust the results on targeted temperature management (hypothermia), as in other observational studies.2,12−15 Nevertheless, it has been clearly established that there is a strong link between this therapy and the neurological outcome, whether or not the rhythm of cardiac arrest is shockable.22–24 Here, we were able to adjust the population on this variable, as well as other numerous factors influencing the outcome. Recently Riva et al. found there was an almost a 2-fold higher rate of CPR before EMS arrival and a concomitant 6-fold higher rate of CO-CPR over time but did not collect neurological outcome at day 30.25
Lay bystanders are more and more often performing CO-CPR
From 2013 to 2017, we observed a clear decrease in S-CPR by lay bystanders to the benefit of CO-CPR (reduction of 50%). The same trends were observed in Sweden during the same period,25 and it has also been observed in other countries.11,15,16 Indeed, since 2010, the International Consensus on Cardiopulmonary Resuscitation has been encouraging untrained people to carry out CO-CPR, and EMS dispatchers must provide CO-CPR instructions by telephone.26 Indeed, in our study there were more dispatcher-assisted CPR in the CO-CPR group and fewer CO-CPR patients received immediate bystander CPR, as it would take time for the dispatcher to explain the mechanics of performing CPR to a bystander. At the end of our study period, there were fewer than 15% of bystanders performing S-CPR. S-CPR can maybe initiate more frequently without delay as public awareness by movies, and television promote early S-CPR more than CO-CPR.
CO-CPR is considered easier to learn and perform. Indeed, at a distance from resuscitation training, the performance of CO-CPR declines only slightly compared to S-CPR.27 In addition, a shorter CO-CPR learning program leads to better performance on chest compressions for the general public.28 Moreover, the learning of mouth-to-mouth during the COVID-19 pandemic period is an issue. Indeed, the risk of contamination via mannequins is real when mouth-to-mouth is performed by all learners.29 Trained people begin CPR more often, resulting in improved OHCA survival.30 CO-CPR teaching must therefore be preferred and recognized as sufficient to obtain a BLS certificate.29
Mouth-to-mouth ventilation is a hindrance to the initiation of CPR because of the risk of disease transmission.31,32 Even though cases of transmission of infectious diseases are rare (less than 1/200 000), they can occur: Neisseria meningitidis, Mycobacterium tuberculosis, enteric pathogens, herpes simplex virus and probably even severe acute respiratory syndrome-associated coronavirus (SARS-CoV).33–35 It seems logical that mouth-to-mouth ventilation increases the risk of transmission of SARS-CoV-2 compared to chest compressions. However, there is no clear evidence that chest compressions result in the generation of aerosol and transmission of infection.36
International Liaison Committee on Resuscitation (ILCOR) and the American Heart Association (AHA) suggest that, as long as the COVID-19 pandemic persists, lay rescuers should consider CO-CPR in adult cardiac arrest.37,38 Furthermore, in the case of non-household bystander, a face mask or cloth covering the mouth and nose of the rescuer and/or victim should be also considered.37 However, COVID-19 may be responsible for acute respiratory distress syndrome (ARDS) requiring mechanical ventilation or even extracorporeal membrane oxygenation (ECMO).39,40 As a result, the incidence of asphyxial OHCA is expected to increase significantly. It is precisely in these situations where the administration of early rescue breaths was thought to be beneficial, but our study suggested that CO-CPR performed by lay bystanders in asphyxial OHCA seemed to be at least equivalent to S-CPR with regard to neurological outcomes.
We did not find improved neurological outcome with S-CPR as opposed to CO-CPR and point-estimate indicates possible better outcome for CO-CPR. The results of previous studies on these non-cardiac causes are discordant. Some did not find a difference between CO-CPR and S-CPR,7,13 while others showed a superiority of S-CPR.2 Another study based on drowning, i.e. hypoxic cardiac arrest, also found no difference between CO-CPR and S-CPR.41 Cause of OHCA was classified by physician in charge of patient during prehospital care with history, clinical, and electric information available. The Utstein style consensus define medical cause as cases in which the cause of the cardiac arrest is presumed to be cardiac, other medical cause (eg, anaphylaxis, asthma, gastro-intestinal bleed), and in which there is no obvious cause of the cardiac arrest and asphyxia causes as external causes of asphyxia, such as foreign-body airway obstruction, hanging, or strangulation.18 But mechanisms of OHCA can be challenged by this categorization as patient who collapse secondary to hypoxemia related to acute left ventricular congestive heart failure will be categorized as “cardiac” whereas “asphyxia” is the determinant of OHCA and ventilation maybe the first therapeutic option.42
Based on our results and previous studies, it can be considered that CO-CPR has many advantages over S-CPR and that it seems logical to continue this CPR practice only in adults, regardless of the cause of medical OHCA, even beyond the COVID-19 pandemic.
First of all, S-CPR and CO-CPR were not assigned by random allocation. In our prospective cohort, we performed an IPTW analysis and made some adjustments for selection bias and confounding factors. Under these conditions, the measured effect was as close as possible to randomized trials.43
Second, an inherent limitation of this type of registry analysis is the lack of completeness of data which may have resulted in not being completely exhaustive in the selection of the population. In order to overcome this bias, as explained above, we have only included centers with high quality data. For example, only 0.9% of the subjects included could not be analyzed due to a lack of neurological outcome (CPC).
Third, the classification of the cause of OHCA was done by the MMT emergency physician. The autopsy data was not available in our registry. This may have led to misclassification of some patients because the causes of OHCA are sometimes difficult to define at an early stage.44
Lastly, the quality of bystander-initiated CPR could not be monitored, and we suppose that those who performed S-CPR were more experienced because we observed a higher rate of immediate resuscitation initiation. Moreover, in the case of inexperienced bystanders, the guidelines recommend that medical dispatchers guide the CO-CPR.