Spotlight on Research

Reducing peri-shock pauses in out-of-hospital cardiac arrest increases odds of survivalFollowing publication of the 2010 American Heart Association-International Liaison Committee on Resuscitation (AHA-ILCOR) guidelines, there has been an increased focus on the characteristic components of cardiopulmonary resuscitation (CPR) including length of peri-shock pause, chest compression fraction (CCF), chest compression depth, chest compression rate and chest compression recoil.This study set out to examine the association between the length of the peri-shock pause and survival from shockable out-of-hospital cardiac arrest (OHCA) using data from patients enrolled in a randomised control trial known as the Resuscitation Outcomes Consortium Prehospital Resuscitation Impedance Valve and Early versus Delayed Analysis (ROC PRIMED).Peri-shock pause is the sum total of both pre- and post-shock pauses. Preshock pause is the time between cessation of chest compressions and the shock being delivered, and postshock pause is the time between shock delivery and resumption of chest compressions.For this study, 2 006 patients (from a total of 15 794 in ROC PRIMED) met the inclusion criteria: adults aged 18 years or older, who had sustained a non-traumatic OHCA and had an initial presenting rhythm of ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) for which CPR process data for at least one shock was obtainable.The primary outcome was survival to hospital discharge and the secondary outcome involved assessment of neurological function using a Modified Rankin Score.During analysis the shock pause length (seconds) was examined categorically, <10, 10–20, ≥20 for pre-shock pauses, <5, 5-10, ≥10 for post-shock pauses and <20, 20–40, ≥40 for peri-shock pauses.Comparison of CPR components demonstrated no significant difference for CCF, compression rate or depth between survivors and non-survivors. For shock pause duration, however, pre-shock pause was 18% shorter (14 seconds versus 17 seconds) for survivors compared to non-survivors; 17% shorter for both postshock pauses (5s vs. 6s) and peri-shock pauses (20 seconds versus 24 seconds) for survivors compared to non-survivors. Pre-, post- and peri-shock pause durations were significantly different (p<0.001) between survivors and non-survivors.Odds ratios were calculated to examine the relationship between pre-, post-, and peri-shock pause duration and survival to hospital discharge. Shorter pre- and peri-shock pauses were significantly associated (p<0.001) with survival to hospital discharge. Specifically, patients experiencing a pre-shock pause of <10 seconds had a higher odds of survival to hospital discharge (OR: 1.52, 95%: 1.09, 2.11) when compared to episodes with a median pre-shock pause of ≥20 seconds. For perishock pause duration, a peri-shock pause of <20 seconds produced a higher odds of survival to hospital discharge (OR; 1.82, 95%: 1.17, 2.85) when compared to peri-shock pause duration of ≥40 seconds. Interestingly, post-shock pause was not significantly associated with survival to hospital discharge.When looking at the relationship between shock pause duration and a positive neurologically intact survival (MRS ≤3), lower pre- and peri-shock pause duration were significantly associated (p<0.001) with positive neurological outcome. The odds of neurologically intact survival were significantly higher with a pre-shock pause <10 seconds (OR: 1.49, 95%: 10.05, 2.13) compared to ≥20 seconds; similarly with the peri-shock pause, the odds of neurologically intact survival were significantly higher if the pause was <20 seconds (OR: 1.99, 95%: 1.21, 3.29) when compared to duration ≥40 seconds.Limitations to the study are that the data are taken retrospectively from other research and are observational. Further investigation would be needed to determine whether the effects of peri-shock pause duration is of a causal relationship. The authors also note that the study is undertaken in a region with a heavily monitored EMS system, with overall rapid response times and high CPR quality, therefore they caution against generalisation to other EMS systems which may not have similar characteristics.The results of this research reinforce the importance of minimising ‘time off the chest’ during CPR attempts, especially during the pre-shock phase supporting the practice of performing chest compressions during the charging phase when using an AED, or using defibrillators in manual mode to reduce pre-shock pause length. Although further research is required, these findings indicate that shortening the peri-shock pause (especially pre-shock) could possibly improve the odds of patients surviving to hospital discharge with favourable neurological outcomes after out-of-hospital cardiac arrest.

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