Abstract
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.