Abstract: We included three randomized controlled trials (RCTs) and one cluster-RCT (with a total of 26,742 participants analysed). We identified one ongoing study. While predominantly adult patients, one study included children. Untrained bystander-administered CPR Three studies assessed CPR provided by untrained bystanders in urban areas of the USA, Sweden and the UK. Bystanders administered CPR under telephone instruction from emergency services. There was an unclear risk of selection bias in two trials and low risk of detection, attrition, and reporting bias in all three trials. Survival outcomes were unlikely to be affected by the unblinded design of the studies. We found high-quality evidence that continuous chest compression CPR without rescue breathing improved participants’ survival to hospital discharge compared with interrupted chest compression with pauses for rescue breathing (ratio 15:2) by 2.4% (14% versus 11.6%; RR 1.21, 95% confidence interval (CI) 1.01 to 1.46; 3 studies, 3031 participants). One trial reported survival to hospital admission, but the number of participants was too low to be certain about the effects of the different treatment strategies on survival to admission(RR 1.18, 95% CI 0.94 to 1.48; 1 study, 520 participants; moderate-quality evidence). There were no data available for survival at one year, quality of life, return of spontaneous circulation or adverse effects. There was insufficient evidence to determine the effect of the different strategies on neurological outcomes at hospital discharge (RR 1.25, 95% CI 0.94 to 1.66; 1 study, 1286 participants; moderate-quality evidence). The proportion of participants categorized as having good or moderate cerebral performance was 11% following treatment with interrupted chest compression plus rescue breathing compared with 10% to 18% for those treated with continuous chest compression CPR without rescue breathing. CPR administered by a trained professional In one trial that assessed OHCA CPR administered by emergency medical service professionals (EMS) 23,711 participants received either continuous chest compression CPR (100/minute) with asynchronous rescue breathing (10/minute) or interrupted chest compression with pauses for rescue breathing (ratio 30:2). The study was at low risk of bias overall. After OHCA, risk of survival to hospital discharge is probably slightly lower for continuous chest compression CPR with asynchronous rescue breathing compared with interrupted chest compression plus rescue breathing (9.0% versus 9.7%) with an adjusted risk difference (ARD) of -0.7%; 95% CI (-1.5% to 0.1%); moderate-quality evidence. There is high-quality evidence that survival to hospital admission is 1.3% lower with continuous chest compression CPR with asynchronous rescue breathing compared with interrupted chest compression plus rescue breathing (24.6% versus 25.9%; ARD -1.3% 95% CI (-2.4% to -0.2%)). Survival at one year and quality of life were not reported. Return of spontaneous circulation is likely to be slightly lower in people treated with continuous chest compression CPR plus asynchronous rescue breathing (24.2% versus 25.3%; -1.1% (95% CI -2.4 to 0.1)), high-quality evidence. There is high-quality evidence of little or no difference in neurological outcome at discharge between these two interventions (7.0% versus 7.7%; ARD -0.6% (95% CI -1.4 to 0.1). Rates of adverse events were 54.4% in those treated with continuous chest compressions plus asynchronous rescue breathing versus 55.4% in people treated with interrupted chest compression plus rescue breathing compared with the ARD being -1% (-2.3 to 0.4), moderate-quality evidence). Following OHCA, we have found that bystander-administered chest compression-only CPR, supported by telephone instruction, increases the proportion of people who survive to hospital discharge compared with conventional interrupted chest compression CPR plus rescue breathing. Some uncertainty remains about how well neurological function is preserved in this population and there is no information available regarding adverse effects. When CPR was performed by EMS providers, continuous chest compressions plus asynchronous rescue breathing did not result in higher rates for survival to hospital discharge compared to interrupted chest compression plus rescue breathing. The results indicate slightly lower rates of survival to admission or discharge, favourable neurological outcome and return of spontaneous circulation observed following continuous chest compression. Adverse effects are probably slightly lower with continuous chest compression. Increased availability of automated external defibrillators (AEDs), and AED use in CPR need to be examined, and also whether continuous chest compression CPR is appropriate for paediatric cardiac arrest.

Plain-language summary: We included four studies; three compared the two approaches to resuscitation when given by untrained bystanders under instruction by telephone. One study compared the two approaches when given by EMS personnel. The three studies, comparing the approaches given by untrained bystanders, (3737 participants) were all undertaken in urban areas and some included both children and adult OHCA. The, bystanders were all untrained and given telephone instructions from the emergency services. The fourth study compared approaches given by EMS professionals (23,711 participants); it was undertaken in urban areas and included only adult OHCA. When CPR was performed by bystanders, we found that more people survived until discharge from hospital after chest compression alone than they did following interrupted chest compression with pauses at a fixed ratio for rescue breathing (15 compressions to 2 breaths) (14% versus 11.6%). For the outcomes of survival to hospital admission and neurological outcomes, we did not have sufficient data to be certain that either strategy was better. No data was available for adverse effects, quality of life or survival at one-year. When CPR was performed by EMS professionals, we found that survival to hospital discharge was slightly lower with continuous chest compressions (100/minute) plus asynchronous rescue breathing (10/minutes) CPR compared with interrupted chest compression plus rescue breathing. Around 9.7% of people lived when they received interrupted chest compression plus rescue breathing compared with 9% of people who received continuous chest compression plus asynchronous rescue breathing. The number of people who survived to hospital admission was slightly higher in those treated with interrupted chest compression plus rescue breathing compared with continuous chest compression plus asynchronous rescue breathing (25.9% versus 24.6%). There was little or no difference in neurological outcomes. The proportion of people who experienced adverse events was probably similar with 55.4% people treated with interrupted chest compression plus rescue breathing experiencing an adverse event compared with 54.4% in those treated with continuous chest compression asynchronous rescue breathing. For bystander-provided CPR, the quality of the evidence was high for the outcome of survival to hospital discharge. For survival to hospital admission, one trial provided results and the evidence was of moderate-quality because of low numbers of people for whom data were available. This was also the case for neurological outcomes. In the one EMS professional-provided CPR trial, the quality of the evidence was moderate for the outcome of survival to hospital discharge because the results do not exclude there being little or no difference between the two approaches, and this is also the case for adverse events. For survival to hospital admission there was high-quality evidence. The main limitation of the current evidence is that only a few trials have been undertaken, and for some outcomes, not enough data have been generated.