Hypothermia is associated with a low ETCO2 and low pH-stat PaCO2 in refractory cardiac arrest

T Darocha,G Debaty,F.X Ageron,P Podsiadło,A Hutin,H Hymczak,M Blancher,S Kosiński,K Mendrala,P.N Carron,L Lamhaut,P Bouzat,M Pasquier

doi:10.1016/j.resuscitation.2022.01.022

Abstract

AimsThe end-tidal carbon dioxide (ETCO2) is frequently measured in cardiac arrest (CA) patients, for management and for predicting survival. Our goal was to study the PaCO2 and ETCO2 in hypothermic cardiac arrest patients. MethodsWe 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 ETCO2 and PaCO2 at hospital admission. We analysed the data according to both alpha-stat and pH-stat strategies. ResultsWe included 131 CA patients (39 hypothermic and 92 non-hypothermic). Both ETCO2 (p < 0.001) and pH-stat PaCO2 (p < 0.001) were significantly lower in hypothermic compared to non-hypothermic patients, which was not the case for alpha-stat PaCO2 (p = 0.15). The median PaCO2-ETCO2 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 ETCO2 (p < 0.01) and pH-stat PaCO2 (p < 0.01) but not with alpha-stat PaCO2 (p = 0.5). The ETCO2 decreased by 0.5 mmHg and the pH-stat PaCO2 by 1.1 mmHg for every decrease of 1° C of the temperature. The proportion of survivors with an ETCO2 ≤ 10 mmHg at hospital admission was 45% (9/25) for hypothermic and 12% (2/17) for non-hypothermic CA patients. ConclusionsHypothermic CA is associated with a decrease of the ETCO2 and pH-stat PaCO2 compared with non-hypothermic CA. ETCO2 should not be used in hypothermic CA for predicting outcome.

Highlights

Both ETCO2 and pH-stat PaCO2 were significantly lower in hypothermic cardiac arrest (CA) than in non-hypothermic CA
Our study showed that ETCO2 should not be used to predict survival in hypothermic CA or as a marker for good quality resuscitation in deep hypothermia
We found that ETCO2 and pH-stat PaCO2 are decreased in hypothermic patients in CA, but not in normothermic patients

Summary

Methods

We included patients with refractory CA assessed for extracorporeal cardiopulmonary resuscitation. We retrospectively analysed patients with refractory CA assessed for ECPR in the emergency department in whom ETCO2 and PaCO2 measurements were available at the time of admission. We included hypothermic CA patients from a previous prospective study[10] and from the Severe Accidental Hypothermia Center, Krakow - Department of Anesthesiology and Intensive Care, John Paul II Hospital, Krakow, Poland. For the non-hypothermic CA patients we analysed de-identified individual patient level data from two primary cohort studies of refractory out-of-hospital cardiac arrest (OHCA) treated with ECPR. The rationale, data collection methods, verification procedures, and primary outcomes have been reported in detail elsewhere.[11,12,13,14,15] The databases for the two observational studies consisted of consecutive, prospectively enrolled refractory OHCA patients. Amongst non-hypothermic CA patients, we excluded patients with prehospital ECPR, CA of non-cardiac or unknown origin, ROSC before hospital admission, patients for whom ETCO2 or

Results

Discussion

Conclusion