End-tidal carbon dioxide measured at emergency department triage outperforms standard triage vital signs in predicting in-hospital mortality and intensive care unit admission

Acad Emerg Med. 2023 Feb 21. doi: 10.1111/acem.14703. Online ahead of print.

Abstract

Objectives: This study assessed the ability of end-tidal carbon dioxide (ETCO2 ) in predicting in-hospital mortality and intensive care unit (ICU) admission compared to standard vital signs at ED triage as well as comparing to measures of metabolic acidosis.

Methods: This prospective study enrolled adult patients presenting to the ED of a tertiary care Level I trauma center over 30 months. Patients had standard vital signs measured along with exhaled ETCO2 at triage. Outcome measures included in-hospital mortality; ICU admission; and correlations with lactate, sodium bicarbonate (HCO3 ), and anion gap.

Results: There were 1136 patients enrolled and 1091 patients with outcome data available. There were 26 (2.4%) patients who did not survive to hospital discharge. Mean ETCO2 levels were 34 (33-34) in survivors and 22 (18-26) nonsurvivors (p < 0.001). The area under the curve (AUC) for predicting in-hospital mortality for ETCO2 was 0.82 (0.72-0.91). In comparison the AUC for temperature was 0.55 (0.42-0.68), respiratory rate (RR) 0.59 (0.46-0.73), systolic blood pressure (SBP) 0.77 (0.67-0.86), diastolic blood pressure (DBP) 0.70 (0.59-0.81), heart rate (HR) 0.76 (0.66-0.85), and oxygen saturation (SpO2 ) 0.53 (0.40-0.67). There were 64 (6%) patients admitted to the ICU, and the ETCO2 AUC for predicting ICU admission was 0.75 (0.67-0.80). In comparison the AUC for temperature was 0.51, RR 0.56, SBP 0.64, DBP 0.63, HR 0.66, and SpO2 0.53. Correlations between expired ETCO2 and serum lactate, anion gap, and HCO3 were rho = -0.25 (p < 0.001), rho = -0.20 (p < 0.001), and rho = 0.330 (p < 0.001), respectively.

Conclusions: ETCO2 was a better predictor of in-hospital mortality and ICU admission than the standard vital signs at ED triage. ETCO2 correlated significantly with measures of metabolic acidosis.

Keywords: emergency; end-tidal carbon dioxide (ETCO2); intensive care unit (ICU); metabolic acidosis; mortality; triage.

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