Service evaluation: Accuracy of using end-tidal CO2 to estimate PaCO2 values in suspected traumatic brain injury patients requiring mechanical ventilation.
Journal of the Intensive Care Society · 2026-04-26 · Method & validation
Abstract
This service evaluation assessed the accuracy of estimating arterial partial pressure of carbon dioxide (PaCO2) from end-tidal CO2 (ETCO2) in prehospital suspected traumatic brain injury (TBI) patients requiring mechanical ventilation. Thirty-one cases with paired ETCO2 and emergency department (ED) PaCO2 measurements were analysed. Estimated PaCO2 (ETCO2 + 0.5 kPa) significantly underestimated measured PaCO2, with a mean bias of 1.17 kPa and wide limits of agreement. Nearly half of patients were outside the normocapnic range despite apparently acceptable estimated values. Findings highlight the risk of inadvertent hypercapnia when relying on ETCO2-based estimation alone. Lower ETCO2 targets or point-of-care PaCO2 measurement may improve ventilation accuracy and reduce secondary brain injury.