Response to Letter Regarding Articles, “Increasing Use of Cardiopulmonary Resuscitation During Out-of-Hospital Ventricular Fibrillation Arrest: Survival Implications of Guideline Changes” and “Measuring Progress in Resuscitation: It’s Time for a Better Tool”
John Stewart comments that recent Guideline changes aimed at increasing CPR should consider whether a manual or automated external defibrillator (AED) is used, since interruptions are more common with the AED, and that future studies should consider defibrillator type as a potential confounder. Science suggests that the ideal resuscitation is one where CPR is not interrupted for rhythm analysis, charge, or pulse checks. The benefit of AED achieved by decreasing the interval from collapse to defibrillation may be offset by other AED features that interrupt CPR; specifically the longer duration required for AED rhythm analysis. Evidence indicates that AED resuscitation using past Guidelines does produce longer CPR interruptions before and after shock than manual defibrillation.1 Importantly, CPR interruptions occurring with manual defibrillation may still be clinically important. Moreover, manual defibrillation is associated with more frequent inappropriate shocks compared with AED, underscoring the importance of training and expertise when undertaking manual defibrillation. Whether inappropriate shocks affect outcome is uncertain, though they presumably introduce additional CPR interruption.
By removing the potential for stacked shocks, new Guidelines eliminate AED-specific interruption following shock but still do not address the excess interruption that occurs for AED analysis before a shock. Through engineering, newer AEDs models have decreased the time for AED analysis and charge, which should attenuate this AED-associated limitation. Importantly, other Guideline changes aimed at delivering more (and more timely) CPR should have similar effects for manual defibrillators and AEDs. Guideline changes eliminate post-shock pulse checks and increase CPR intervals from 1 to 2 minutes, changes which should reduce CPR interruption regardless of defibrillator type.
In summary, Guidelines changes should increase CPR for AED and manual defibrillation. The impact will typically be greater for the AED so that past differences in CPR delivery between manual and AED defibrillation should be attenuated. Nonetheless, with optimal use, manual defibrillation still provides efficiencies that could positively influence outcome. Simple measurement of defibrillator type may incorporate multiple differences, since defibrillator type may be a surrogate for other distinct treatments and/or experience. An alternate approach is to measure hands-off intervals before and after shock, or throughout resuscitation. Careful analysis may help quantitate potential outcome advantages of manual defibrillation and in turn provide a more informed framework for how to use limited resources aimed at improving resuscitation.