Minimizing pauses or interruptions in chest compressions before a defibrillator shock for cardiac arrest may maximize survival according to the latest research. This is stressed in AHA guidelines because of prior studies of inhospital cardiac arrest outcomes in prior studies.
For every additional five seconds of delay, the chance of survival to hospital discharge was reduced by 18% for pauses before administering the shock. It was reduced by 14% for overall delays before or after the shock.
Each additional five seconds of delay reduced the chance of survival to hospital discharge by 18% for pauses before administering the shock and by 14% for overall delays before or after the shock in registry data analyzed by Sheldon Cheskes, MD, of the University of Toronto, and colleagues.
“Refinement of automatic defibrillator software and paramedic education to minimize preshock pause delays may have a significant impact on survival,” Sheldon Cheskes, MD, of the University of Toronto, and colleagues wrote in the July 5 issue of Circulation: Journal of the American Heart Association.
One important contributor to interruptions is the time a defibrillator takes to sense whether the cardiac rhythm is shockable and to deliver the shock.
Unfortunately, current defibrillator software has built in pauses, though for safety of those performing CPR.
According to Cheskes’ group, “Defibrillator software that permits underlying rhythm analysis during CPR and battery charging, and delivery of a shock immediately at the end of the CPR interval could significantly decrease the preshock pause interval. Improved algorithms allowing earlier detection of shockable rhythms while working in the automated mode could also decrease the preshock pause time.”
The study reflects the High Performance CPR classes that I wrote about a few days ago.
About the study:
They analyzed results for 815 out-of-hospital cardiac arrests documented in the Resuscitation Outcomes Consortium cardiac arrest registry from December 2005 to June 2007 with a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia).
Five emergency medical services agencies across Canada and in the U.S. provided the data. Cases in which defibrillators in public places were used before EMS arrival or without data on survival to hospital discharge were excluded.
The registry indicated a median preshock pause of 15.6 seconds (with a range of up to 107 seconds) and median postshock pause of 8.3 seconds (with a range up to 220 seconds).
The odds of survival were 53% lower with a pause of 20 seconds or more, compared with less than 10 seconds before administering the shock (odds ratio 0.47, 95% confidence interval 0.27 to 0.82).
Waiting a total of 40 seconds or more before or after the shock was associated with 46% lower odds of survival than with a pause of less than 20 seconds (OR 0.54, 95% CI 0.31 to 0.97).
Return of spontaneous circulation in the emergency department was also less likely with longer delays in the same comparisons (OR 0.37 for preshock, 95% CI 0.20 to 0.71, and OR 0.52 overall, 95% CI 0.27 to 0.97).
Postshock delays on their own were not statistically or independently predictive of outcomes. The investigators speculated that rapid resumption of chest compressions post shock might actually trigger recurrent ventricular fibrillation.
Pre- and postshock pauses generally decreased the more shocks a person received.
Manual mode on the defibrillator reduced preshock pauses (median 10.0 versus 18.0 seconds in automatic mode, P<0.001).
The researchers cautioned that their study could not determine causal relationships and did not adjust for certain potentially important variables like inhospital care and chest compression rate.
Also the study took place in regions with optimized EMS response times, which may appear to benefit most from changes in CPR guidelines and shortened pause intervals, the researchers noted. Applicability to other nonoptimized systems is uncertain, they added.