Literature Review: Perishock Pauses and Survival to Discharge

Cheskes S, Schmicker RH, Christenson J, et al. Perishock pause: An independent predictor of survival from out-of-hospital shockable cardiac arrest. Circ 124(1): 58–66, Jul 5, 2011.

Abstract

Perishock pauses are pauses in chest compressions before and after defibrillatory shock. The authors examined the relationship between perishock pauses and survival to hospital discharge. Methods and Results—Out-of-hospital cardiac arrest patients in the Resuscitation Outcomes Consortium Epistry-Cardiac Arrest who suffered arrest between December 2005 and June 2007, presented with a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia), and had cardiopulmonary resuscitation process data for at least one shock (n=815) were included. Multivariable logistic regression was used to determine the association between survival and perishock pauses. In an analysis adjusted for Utstein predictors of survival, the odds of survival were significantly lower for patients with preshock pauses greater than or equal to 20 seconds (odds ratio 0.47) and perishock pauses greater than or equal to 40 seconds (OR 0.54) compared with patients with preshock pauses less than 10 seconds and perishock pauses less than 20 seconds. Postshock pause was not independently associated with a significant change in the odds of survival. Log-linear modeling depicted a decrease in survival to hospital discharge of 18% and 14% for every 5-second increase in both preshock and perishock pause interval (up to 40 and 50 seconds, respectively), with no significant association noted with changes in the postshock pause interval.

Conclusions—In patients with cardiac arrest presenting in a shockable rhythm, longer perishock and preshock pauses were independently associated with a decrease in survival to hospital discharge. The impact of preshock pause on survival suggests that refinement of automatic defibrillator software and paramedic education to minimize preshock pause delays may have a significant impact on survival.

Comment

The value of high-quality (rate, depth, recoil) uninterrupted chest compressions is well known. This study points out that minimizing the interval between the last compression and the defibrillation shock may be especially important, with an 18% decrease in survival for every additional five seconds of increase in that interval’s duration. One of the effects of chest compressions is to create blood flow to the myocardium, and this increases the success rate of defibrillation shocks. However, the coronary perfusion pressure drops within seconds of stopping CPR, so pauses will quickly reduce the effectiveness of defibrillation attempts.

Improving performance requires training, attention and teamwork—a coordinated effort between the individuals performing chest compressions, ventilations (if any) and defibrillation. Protocol changes might include resuming chest compressions during defibrillator charging and pausing advanced airway attempts or other procedures. Advances such an insulating “resuscitation blanket” may eventually allow defibrillation during continuous compressions. EMS systems should consider establishing a routine process of reviewing monitor downloads on all cardiac arrests, with an evaluation of CPR quality and preshock intervals as a focus.

Angelo Salvucci, Jr., MD, FACEP, is medical director for the Santa Barbara County and Ventura County (CA) EMS agencies and a member of EMS World's editorial advisory board.