Linear regression plots illustrating PaCO2 and ETCO2 agreement in patients with Isolated-TBI versus TBI+, admitted to the Intensive Care Unit at Cambridge University Hospitals NHS Foundation Trust; 2015–2019.

ETCO2—End-tidal carbon dioxide, PaCO2 –partial pressure of arterial carbon dioxide, TBI—traumatic brain injury, Isolated-TBI—patients with serious or more severe isolated TBI, with no concomitant injuries (AIS ≥3 ‘head’ only), TBI+—patients with serious or more severe TBI plus concomitant injuries (AIS ≥3 ‘head’ together with at least one other anatomical body region AIS ≥1).