Abstract 18435: ETCO2 Alone is Inadequate to Verify CPR Quality

Abstract

Background: Previous studies have described modest correlation between end-tidal CO₂ (ETCO₂) and CPR quality during resuscitation of cardiac arrest patients, but it is unclear whether ETCO₂ alone can indicate CPR quality. The present study investigated whether ETCO₂ adequately identifies the quality of CPR provided during out-of-hospital cardiac resuscitation.

Methods: ETCO₂ was monitored with side-stream CO₂ (Philips/Respironics) and CPR quality measured with an accelerometer-based system (E Series, ZOLL Medical) during the treatment of consecutive adult OHCA patients with presumed cardiac etiology by 2 EMS agencies in the Arizona SHARE QI Program between 10/08-06/13. Minute-by-minute ETCO₂ and CPR quality were extracted. ETCO₂ values were log transformation to achieve approximate normality. Linear mixed effect models were fitted to use (transformed) ETCO₂ level to predict four CPR variables: chest compression (CC) depth, CC rate, CC release velocity (CCRV), and ventilation rate (VR). A random intercept for each case was included and a spatial power covariance structure assumed for measurements over time.

Results: 230 subjects (median age 69 yrs, 69% male) with 1581 minutes of data were studied. Transformed ETCO₂ was significant for CC depth (p< 0.0001), CCRV (p=0.003) and VR (p<0.0001), but only explained 3.7%, 2.7%, and 10.0% of the total variance for these variables, respectively. Transformed ETCO₂ was not a significant predictor for CC rate (p=0.89). The Figure illustrates the overlap in CC depth over quartiles of ETCO₂, demonstrating that any specific ETCO₂ level could be found over a wide range of CC depths.

Conclusion: In this secondary analysis, ETCO₂ was not an independent indicator of CC rate but was a weak predictor for CC depth, CCRV and VR. These findings suggest that ETCO₂ may be not be an adequate substitute for CPR quality monitoring. Future studies should investigate how ETCO₂ and CPR quality monitoring can be used in conjunction to optimize CPR.