Background: The lack of an accurate marker of prehospital hemorrhagic shock limits our ability to triage patients to the correct level of care, delays treatment in the emergency department, and inhibits our ability to perform prehospital interventional research in trauma. End-tidal carbon dioxide (ETCO2) is the measurement of alveolar carbon dioxide concentration at end expiration and is measured noninvasively in the ventilator circuit for intubated patients in continuous manner. Several hospital-based studies have been able to demonstrate that either low or decreasing levels of ETCO2 as well as disparities between ETCO2 and plasma carbon dioxide correlate with increasing mortality in trauma. We hypothesized that prehospital ETCO2 values will be predictive of mortality and need for massive transfusion following injury.
Methods: This is a single-center retrospective study from an urban level 1 trauma center. We reviewed all intubated adult patients transported for injury who had prehospital ETCO2 values available. Unadjusted comparisons of continuous variables were done with the Wilcoxon two-sample test. The predictive performance of prehospital ETCO2, the prehospital shock index, and prehospital systolic blood pressure were assessed and compared using areas under the receiver operating characteristic curves. Optimal cutoffs were estimated by maximizing the Youden index. Massive transfusion was defined as >10 U of blood or death in 24 hours.
Results: A total of 173 patients were identified with prehospital ETCO2 values during the 2-year study period. Population was 78.5% male with a median age of 37.5 years (interquartile range, 23.5-53.5 years). Injury mechanism was penetrating in 22.8%. This cohort had a median Injury Severity Score of 26 (interquartile range, 17-36), massive transfusion rate of 34.7%, and mortality of 42.1%. In the evaluation of prediction of postinjury mortality and massive transfusion, ETCO2 outperformed systolic blood pressure and shock index, but these differences did not reach statistical significance.
Conclusion: End-tidal carbon dioxide is a novel prehospital predictor of mortality and massive transfusion after injury.
Level of evidence: Prognostic/Epidemiologic, level III.