Prehospital End-tidal Carbon Dioxide Predicts Mortality in Trauma Patients

Abstract

Background: End-tidal carbon dioxide (EtCO₂) measurement has been shown to have prognostic value in acute trauma. Objective: Evaluate the association of prehospital EtCO₂ and in-hospital mortality in trauma patients and to assess its prognostic value when compared to traditional vital signs. Methods: Retrospective, cross-sectional study of patients transported by a single EMS agency to a level one trauma center. We evaluated initial out-of-hospital vital signs documented by EMS personnel including EtCO₂, respiratory rate (RR), systolic BP (SBP), diastolic BP (DBP), pulse (P), and oxygen saturation (O₂) and hospital data. The main outcome measure was mortality. Results: 135 trauma patients were included; 9 (7%) did not survive. The mean age of patients was 40 (SD17) [Range 16–89], 97 (72%) were male, 76 (56%) were admitted to the hospital and 15 (11%) went to the ICU. The mean EtCO2 level was 18 mmHg (95%CI 9–28) [Range 5–41] in non-survivors compared to 34 mmHg (95%CI 32–35) [Range 11–51] in survivors. The area under the ROC curve (AUC) for EtCO₂ in predicting mortality was 0.84 (0.67–1.00) (p = 0.001), RR was 0.82 (0.63–1.00), SBP was 0.72 (0.49–0.96), DBP was 0.72 (0.47–0.97), pulse was 0.51 (0.26–0.76), and O₂ was 0.64 (0.37–0.91). Cut-off values at 30 mmHg yielded sensitivity = 89% (51–99), specificity = 68% (59–76), PPV = 13% (6–24) and NPV = 99% (93–100) for predicting mortality. There was no correlation between RR and EtCO₂ (correlation 0.16; p = 0.06). Conclusion: We found an inverse association between prehospital EtCO₂ and mortality. This has implications for improving triage and assisting EMS in directing patients to an appropriate trauma center.

Key words:

• prehospital
• trauma
• capnography
• end-tidal carbon dioxide
• vital signs