Partial pressure of arterial carbon dioxide after resuscitation from cardiac arrest and neurological outcome: A prospective multi-center protocol-directed cohort study

Aims: Partial pressure of arterial carbon dioxide (PaCO ₂ ) is a regulator of cerebral blood flow after brain injury. We sought to test the association between PaCO ₂ after resuscitation from cardiac arrest and neurological outcome. Methods: A prospective protocol-directed cohort study across six hospitals. Inclusion criteria: age ≥18, non-traumatic cardiac arrest, mechanically ventilated after return of spontaneous circulation (ROSC), and receipt of targeted temperature management. Per protocol, PaCO ₂ was measured by arterial blood gas analyses at one and six hours after ROSC. We determined the mean PaCO ₂ over this initial six hours after ROSC. The primary outcome was good neurological function at hospital discharge, defined a priori as a modified Rankin Scale ≤3. Multivariable Poisson regression analysis was used to test the association between PaCO ₂ and neurological outcome. Results: Of the 280 patients included, the median (interquartile range) PaCO ₂ was 44 (37–52) mmHg and 30% had good neurological function. We found mean PaCO ₂ had a quadratic (inverted “U” shaped) association with good neurological outcome, with a mean PaCO ₂ of 68 mmHg having the highest predictive probability of good neurological outcome, and worse neurological outcome at higher and lower PaCO ₂ . Presence of metabolic acidosis attenuated the association between PaCO ₂ and good neurological outcome, with a PaCO ₂ of 51 mmHg having the highest predictive probability of good neurological outcome among patients with metabolic acidosis. Conclusion: PaCO ₂ has a “U” shaped association with neurological outcome, with mild to moderate hypercapnia having the highest probability of good neurological outcome.