Association between arterial to end-tidal carbon dioxide gradient and prehospital hemodynamic status in patients with moderate-to-severe traumatic brain injury

We aimed to assess the relationship between arterial partial pressure of carbon dioxide (PaCO 2 ) and end-tidal carbon dioxide (EtCO 2 ) according to three prehospital hemodynamic status and to evaluate whether hemodynamic-based EtCO₂ targets could improve agreement with PaCO₂. Over a 4-year period, 100 adult patients with moderate-to-severe TBI admitted to a level 1 trauma center under mechanical ventilation were retrospectively included. Patients were classified into three clusters based on prehospital hemodynamic status (Cluster 1: Stable without vasopressors; Cluster 2: Stabilized with low-dose vasopressors; Cluster 3: Not stabilized with low-dose vasopressors). Correlation and agreement between paired PaCO₂ and EtCO₂ values were assessed overall and across clusters. Agreement was compared between non-adjusted and cluster-adjusted EtCO₂ thresholds. The mean PaCO 2 - EtCO 2 gradient increased according to the hemodynamic status (Cluster 1: 3.5 ± 5.5 mmHg, Cluster 2: 9.9 ± 7.3 mmHg, Cluster 3: 12.6 ± 9.5 mmHg). The agreement between paired PaCO 2 and non-adjusted EtCO 2 levels decreased between the three clusters (61% [95%CI: 44–77%] in Cluster 1, 42% [95%CI: 25–59%] in Cluster 2, 31% [95%CI: 16–46%] in Cluster 3). Adjusting EtCO₂ targets according to hemodynamic status did not improve agreement between pairs (53% vs. 44%, p = 0.204). In moderate-to-severe TBI, there is a strong relationship between the PaCO₂–EtCO₂ gradient and prehospital hemodynamic status. However, our results did not support the relevance of a prehospital ventilation strategy guided by cluster-adjusted EtCO₂ targets.