Hypothermia is associated with a low ETCO2 and low pH-stat PaCO2 in refractory cardiac arrest
Tomasz Darocha, Guillaume Debaty, François‐Xavier Ageron, Paweł Podsiadło, Alice Hutin, Hubert Hymczak, Marc Blancher, Sylweriusz Kosiński, Konrad Mendrala, Pierre‐Nicolas Carron, Lionel Lamhaut, Pierre Bouzat, Mathieu Pasquier
Abstract
The end-tidal carbon dioxide (ETCO 2 ) is frequently measured in cardiac arrest (CA) patients, for management and for predicting survival. Our goal was to study the PaCO 2 and ETCO 2 in hypothermic cardiac arrest patients. Methods: We included patients with refractory CA assessed for extracorporeal cardiopulmonary resuscitation. Hypothermic patients were identified from previously prospectively collected data from Poland, France and Switzerland. The non-hypothermic CA patients were identified from two French cohort studies. The primary parameters of interest were ETCO 2 and PaCO 2 at hospital admission. We analysed the data according to both alpha-stat and pH-stat strategies. Results: We included 131 CA patients (39 hypothermic and 92 non-hypothermic). Both ETCO 2 (p < 0.001) and pH-stat PaCO 2 (p < 0.001) were significantly lower in hypothermic compared to non-hypothermic patients, which was not the case for alpha-stat PaCO 2 (p = 0.15). The median PaCO 2 -ETCO 2 gradient was greater for hypothermic compared to non-hypothermic patients when using the alpha-stat method (46 mmHg vs 30 mmHg, p = 0.007), but not when using the pH-stat method (p = 0.10). Temperature was positively correlated with ETCO 2 (p < 0.01) and pHstat PaCO 2 (p < 0.01) but not with alpha-stat PaCO 2 (p = 0.5). The ETCO 2 decreased by 0.5 mmHg and the pH-stat PaCO 2 by 1.1 mmHg for every decrease of 1C of the temperature. The proportion of survivors with an ETCO 2 10 mmHg at hospital admission was 45% (9/25) for hypothermic and 12% (2/17) for non-hypothermic CA patients. Conclusions: Hypothermic CA is associated with a decrease of the ETCO 2 and pH-stat PaCO 2 compared with non-hypothermic CA. ETCO 2 should not be used in hypothermic CA for predicting outcome.