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Health See other Health Articles Title: Delay Between CPR and Defibrillator Shock Decreases Survival June 20, 2011 (Toronto, Ontario) — Reducing the delay between chest compressions and the delivery of defibrillator shocks during the treatment of out-of-hospital cardiac arrest will improve the patient's chances of surviving to discharge, the results of a new study published online June 20, 2011 in Circulation show [1]. Dr Sheldon Cheskes (University of Toronto, ON) and colleagues analyzed the detailed cardiopulmonary resuscitation (CPR) data collected by electronic defibrillators from 815 patients in the Resuscitation Outcomes Consortium (ROC) Epistry treated for an out-of-hospital cardiac arrest with ventricular fibrillation or pulseless ventricular tachycardia. Their analysis shows that the odds of a patient surviving to hospital discharge were significantly lower when the time between stopping the CPR compressions and beginning the defibrillation shock (the preshock pause) was 20 seconds or longer vs preshock pauses under 10 seconds (odds ratio 0.47). However, the length of the postshock pause before resumption of CPR compressions after a shock was not independently associated with a significant change in survival. The statistical modeling shows that the patients' odds of surviving to hospital discharge decreases by 18% for every five-second increase in the preshock interval. "This was the first study able to show the relationship between shock pause and survival to discharge," Cheskes told heartwire . "Most of the other studies that have been done in this area were done with a smaller number of patients and showed an improvement in return of circulation and that patients got pulses back but didn't have enough patients to say that more patients survive [with a shorter preshock pause]." Cheskes also pointed out that most of the previous studies on the delays between compressions and defibrillation and between defibrillation and more compressions suggested that both preshock and postshock delay led to worse outcomes, but this relatively large data set shows that only the preshock pause matters. "That was an interesting finding, and we probably need some further research to tease out why the postshock pause wasn't a significant finding," he said. Cheskes et al observe that the lack of association between postshock pause and survival appears to be supported by recent data from the Amsterdam Resuscitation Study (ARREST) study showing that ventricular fibrillation recurs sooner and more frequently when the postshock chest compressions begin immediately following a shock than when the postshock chest compressions are delayed. The benefits of a higher chest-compression fraction, the proportion of time spent performing chest compressions, may be offset by the harm of earlier recurrent VF in patients with shorter postshock pauses, Cheskes et al suggest. However, this new study was unable investigate the issue of refibrillation because the defibrillator software that eliminates CPR artifacts and allows the provider to accurately assess the underlying rhythm was not universally available at the time of this study (2005 to 2007). In response to this research, Cheskes's center has made a collective effort to decrease the preshock pause when treating out-of-hospital cardiac-arrest patients. The researchers have found that preshock delay is shorter when the defibrillator is in manual mode than it is in automatic mode. In automatic mode, the defibrillator electronically reads the patient's underlying rhythm to determine if it's shockable and then sends a message to the operator to provide a shock. In manual mode, the operator reads and interprets the rhythm and delivers the shock as soon as it is determined the rhythm is shockable. "We used to work in automatic mode but now we use the manual mode. We give paramedics a maximum of five seconds at the end of the two-minute CPR interval to decide if they should deliver a shock or resume CPR. We're now seeing preshock pauses around the three- to five-second mark, much less than the 18 to 20 seconds we had when we were working in automatic mode," Cheskes said. "We've already begun the transition based on this research. Time will tell if that improves the survival rate." Since many patients with out-of-hospital arrest are treated by untrained bystanders who cannot effectively operate a defibrillator in manual mode, this research should give automatic external defibrillator manufacturers more incentive to improve their devices to reduce the preshock delay, Cheskes said. The study was supported by grants from the Resuscitation Outcomes Consortium. The authors report no potential conflicts of interest
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