Maximum Value of End-Tidal Carbon Dioxide Concentrations during Resuscitation as an Indicator of Return of Spontaneous Circulation in out-of-Hospital Cardiac Arrest.

Background: The end-tidal carbon dioxide (ETCO2 ) concentration during resuscitation (CPR) of an out-of-hospital cardiac arrest (OHCA) has an increasingly well-known prognostic value. Nevertheless, few studies have investigated its maximum value in different etiologies. Methods: It was a retrospective, observational, multicentre study from the French OHCA Registry. All adult OHCA with a known maximum value of ETCO2 during CPR were included. The primary end-point was to determine the area under the receiver operating characteristic curve (AUROC) of the maximum value of ETCO2 during resuscitation for the return of spontaneous circulation (ROSC). Results: Of the 53,048 eligible subjects from 2011 to 2018, ETCO2 was known in 32,249 subjects (61%). Among them, there were 9.2% of traumatic OHCA, 37.7% of suspected cardiac etiology and 16.4% of suspected respiratory etiology. The AUROC of maximum value of ETCO2 during CPR to achieve ROSC was 0.887 95CI [0.875-0.898] in traumatic OHCA, 0.772 95CI [0.765-0.780] in suspected cardiac etiology and 0.802 95CI [0.791-0.812] in suspected respiratory etiology. The threshold with no survivors at d-30 was <10 mmHg for traumatic etiologies and <6 mmHg for suspected cardiac and respiratory causes. The probability of ROSC increased with the value of ETCO2 in the 3 etiologies studied. Conclusions: The maximum value of ETCO2 during OHCA resuscitation was strongly associated with ROSC, especially in the case of a traumatic cause. This suggests that a single elevated ETCO2 value, regardless of time, could help to predict the outcome.