Out-of-Hospital Arterial to End-Tidal Carbon Dioxide Gradient in Patients With Return of Spontaneous Circulation After Out-of-Hospital Cardiac Arrest: A Retrospective Study.

Study Objective: End-tidal carbon dioxide (etCO) is used to guide ventilation after achieving return of spontaneous circulation (ROSC) in certain out-of-hospital systems, despite an unknown difference between arterial and end-tidal CO (partial pressure of carbon dioxide [paCO]-etCO difference) levels in this population. The primary aim of this study was to evaluate and quantify the paCO-etCO difference in out-of-hospital patients with ROSC after nontraumatic cardiac arrest.

Methods: This retrospective single-center study included patients aged 18 years and older with sustained ROSC after nontraumatic out-of-hospital cardiac arrest. In patients with an existing out-of-hospital arterial blood gas analysis within 30 minutes after achieving ROSC, matching etCO values were evaluated. Linear regression and Bland-Altman plot analysis were performed to ascertain the primary endpoint of interest.

Results: We included data of 60 patients in the final analysis. The mean paCO-etCO difference was 32 (±18) mmHg. Only a moderate correlation (R=0.453) between paCO and etCO was found. Bland-Altman analysis showed a bias of 32 mmHg (95% confidence interval [CI], 27 to 36) [the upper limit of agreement of 67 mmHg (95% CI, 59 to 74) and the lower limit of agreement of -3 mmHg (95% CI, -11 to 5)].

Conclusion: The paCO-etCO difference in patients with ROSC after out-of-hospital cardiac arrest is far from physiologic ranges, and the between-patient variability is high. Therefore, etCO-guided adaption of ventilation might not provide adequate accuracy in this setting.