Lit Matters #2: Triage End-tidal Carbon Dioxide vs Standard Vital Signs

Low end-tidal carbon dioxide at ED triage is a stronger early warning sign for in-hospital mortality and ICU admission than standard vital signs alone. In undifferentiated emergency patients, ETCO2 appears to track illness severity through acidosis and poor perfusion better than pulse, blood pressure, respiratory rate, or oxygen saturation.

Triage End-tidal CO2 Risk Stratification

• Low ETCO2 signal: A low triage ETCO2 was the clearest abnormality linked to bad outcomes, with non-survivors clustering around 22 mmHg versus about 35 mmHg in survivors.
• Outperforming standard vitals: ETCO2 beat every routine triage vital sign for predicting both mortality and ICU admission, with mortality discrimination reaching an AUC range of 0.82 to 0.88.
• Useful rule-out profile: An abnormal ETCO2 threshold carried a negative predictive value of 99% for mortality, making it most attractive as an early reassurance tool when the number is normal.
• Perfusion and acidosis link: The physiologic signal is probably downstream of poor perfusion and metabolic acidosis, supported by correlations with lactate, bicarbonate, and anion gap.
• Normal versus abnormal framing: The practical bedside takeaway is to treat ETCO2 like another vital sign: normal is reassuring, abnormal deserves attention, and the exact cut points are worth hearing in the episode.
• Gestalt comparison gap: What this study still does not answer is whether ETCO2 adds value beyond an experienced triage nurse or physician's first-look gestalt.