• Heemun Kwok, Jason Coult, Chenguang Liu, Jennifer Blackwood, Peter J Kudenchuk, Thomas D Rea, and Lawrence Sherman.
• Center for Progress in Resuscitation, University of Washington, Seattle, WA, United States; Department of Medicine, University of Washington School of Medicine, Seattle, WA, United States. Electronic address: heemun@uw.edu.
• Resuscitation. 2016 Aug 1; 105: 22-8.

ObjectiveReal-time feedback improves CPR performance. Chest compression data may be obtained from an accelerometer/force sensor, but the impedance signal would serve as a less costly, universally available alternative. The objective is to assess the performance of a method which detects the presence/absence of chest compressions and derives CPR quality metrics from the impedance signal in real-time at 1s intervals without any latency period.MethodsDefibrillator recordings from cardiac arrest cases were divided into derivation (N=119) and validation (N=105) datasets. With the force signal as reference, the presence/absence of chest compressions in the impedance signal was manually annotated (reference standard). The method classified the impedance signal at 1s intervals as Chest Compressions Present, Chest Compressions Absent or Indeterminate. Accuracy, sensitivity and specificity for chest compression detection were calculated for each case. Differences between method and reference standard chest compression fractions and rates were calculated on a minute-to-minute basis.ResultsIn the validation set, median accuracy was 0.99 (IQR 0.98, 0.99) with 2% of 1s intervals classified as Indeterminate. Median sensitivity and specificity were 0.99 (IQR 0.98, 1.0) and 0.98 (IQR 0.95, 1.0), respectively. Median chest compression fraction error was 0.00 (IQR -0.01, 0.00), and median chest compression rate error was 1.8 (IQR 0.6, 3.3) compressions per minute.ConclusionA real-time method detected chest compressions from the impedance signal with high sensitivity and specificity and accurately estimated chest compression fraction and rate. Future investigation should evaluate whether an impedance-based guidance system can provide an acceptable alternative to an accelerometer-based system.Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

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