Quantitative relationship between end-tidal carbon dioxide and CPR quality during both in-hospital and out-of-hospital cardiac arrest.

Objective: Cardiopulmonary resuscitation (CPR) guidelines recommend the administration of chest compressions (CC) at a standardized rate and depth without guidance from patient physiologic output. The relationship between CC performance and actual CPR-generated blood flow is poorly understood, limiting the ability to define "optimal" CPR delivery. End-tidal carbon dioxide (ETCO2) has been proposed as a surrogate measure of blood flow during CPR, and has been suggested as a tool to guide CPR despite a paucity of clinical data. We sought to quantify the relationship between ETCO2 and CPR characteristics during clinical resuscitation care.
Methods: Multicenter cohort study of 583 in- and out-of-hospital cardiac arrests with time-synchronized ETCO2 and CPR performance data captured between 4/2006 and 5/2013. ETCO2, ventilation rate, CC rate and depth were averaged over 15-s epochs. A total of 29,028 epochs were processed for analysis using mixed-effects regression techniques.
Results: CC depth was a significant predictor of increased ETCO2. For every 10mm increase in depth, ETCO2 was elevated by 1.4mmHg (p<.001). For every 10 breaths/min increase in ventilation rate, ETCO2 was lowered by 3.0mmHg (p<.001). CC rate was not a predictor of ETCO2 over the dynamic range of actual CC delivery. Case-averaged ETCO2 values in patients with return of spontaneous circulation were higher compared to those who did not have a pulse restored (34.5±4.5 vs 23.1±12.9mmHg, p<.001).
Conclusions: ETCO2 values generated during CPR were statistically associated with CC depth and ventilation rate. Further studies are needed to assess ETCO2 as a potential tool to guide care.
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