Service evaluation: Accuracy of using end-tidal CO₂ to estimate PaCO₂ values in suspected traumatic brain injury...

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.