The association between arterial-end-tidal carbon dioxide difference and outcomes after out-of-hospital cardiac arrest

Abstract

Aim: We sought to determine if the difference between P_aCO₂ and E_TCO₂ is associated with hospital mortality and neurologic outcome following out-of-hospital cardiac arrest (OHCA).

Methods: This was a retrospective cohort study of adult patients who achieved return of spontaneous circulation (ROSC) after OHCA over 3 years. The primary exposure was the P_aCO₂-E_TCO₂ difference on hospital arrival. The primary outcome was survival to hospital discharge. The secondary outcome was favorable neurologic status at discharge. We used receiver operating characteristic (ROC) curves to determine discrimination threshold and multivariate logistic regression to examine the association between the P_aCO₂-E_TCO₂ difference and outcome.

Results: Of 698 OHCA patients transported to the hospitals, 381 had sustained ROSC and qualifying E_TCO₂ and P_aCO₂ values. Of these, 160 (42%) survived to hospital discharge. Mean E_TCO₂ was 39 mmHg among survivors and 43 mmHg among non-survivors. Mean P_aCO₂-E_TCO₂ was 6.8 mmHg and 9.0 mmHg (p < 0.05) for survivors and non-survivors. After adjustment for Utstein characteristics, a higher P_aCO₂-E_TCO₂ difference on hospital arrival was not associated with hospital mortality (OR 0.99, 95% CI: 0.97-1.0) or neurological outcome. Area under the ROC curve or P_aCO₂-E_TCO₂ difference was 0.56 (95% CI 0.51-0.62) compared with 0.58 (95% CI 0.52-0.64) for E_TCO₂.

Conclusion: Neither P_aCO₂-E_TCO₂ nor E_TCO₂ were strong predictors of survival or neurologic status at hospital discharge. While they may be useful to guide ventilation and resuscitation, these measures should not be used for prognostication after OHCA.

Keywords: Arterial carbon dioxide; Cardiac arrest; End tidal carbon dioxide; OHCA; Out-of-hospital cardiac arrest.