Utility of end-tidal carbon dioxide to guide resuscitation termination in prolonged out-of-hospital cardiac arrest

Study objective: To evaluate if the change in end-tidal carbon dioxide (ETCO2) over time has improved discriminatory value for determining resuscitation futility compared to a single ETCO2 value in prolonged, refractory non-shockable out-of-hospital cardiac arrest (OHCA). Methods: This is a retrospective analysis of adult refractory non-shockable, non-traumatic OHCA patients in the Portland Cardiac Arrest Epidemiologic Registry (PDX Epistry) from 2018 to 2021. We defined refractory non-shockable OHCA cases as patients with lack of a shockable rhythm at any time or return of spontaneous circulation at any time prior to 30-min of on-scene resuscitation. We abstracted ETCO2 values first recorded after advanced airway placement and nearest to the 30-min mark of on-scene resuscitation (30 min-ETCO2) from EMS charts. The primary outcome was survival to hospital discharge. We compared 30 min-ETCO2 cutoffs of 10 mmHg and 20 mmHg to the trend (increasing or not) from initial to 30 min-ETCO2 (delta-ETCO2) using sensitivity, specificity, and area under the receiver operating curves (AUROC). Results: Of 3837 adult OHCA, 2850 were initially non-shockable, and there were 617 (16.1%) cases of refractory non-shockable OHCA at 30-min. We excluded 320 cases without at least two ETCO2 recordings in the EMS chart, leaving 297 cases that met inclusion criteria. Of these, 176 (59.3%) were transported and 2 (0.7%) survived to discharge. Using absolute 30 min-ETCO2 cutoffs, both survivors were in the >10 mmHg group (sensitivity 100.0%, specificity 12.5%), whereas only one survivor was identified in the >20 mmHg group (sensitivity 50.0%, specificity 32.5%). Using delta-ETCO2, both survivors were in the increasing ETCO2 group (sensitivity 100.0%, specificity 60.7%). In comparing the two tests that did not misclassify survivors, the AUROC [95% CI] was higher when using delta-ETCO2 (0.803 [0.775–0.831]) compared to an absolute cutoff of 10 mmHg (0.563 [0.544–0.582]). Conclusions: Nearly one-sixth of EMS-treated adult OHCA patients had refractory non-shockable arrests after at least 30 min of ongoing resuscitation. In this group, the ETCO2 trend following advanced airway placement may be more accurate in guiding termination of resuscitation than an absolute ETCO2 cutoff of 10 or 20 mmHg.