Association between postresuscitation partial pressure of arterial carbon dioxide and neurological outcome in patients with post - Cardiac arrest syndrome

Background: - Partial pressure of arterial CO₂ (PaCO ₂) iS a regulator of cerebral blood flow after brain injury. Recent guidelines for the management of cardiac arrest recommend maintaining PaCO ₂ at 40 to 45 mm Hg after successful resuscitation; however, there is a paucity of data on the prevalence of PaCO₂ derangements during the post - cardiac arrest period and its association with outcome. Methods and Results: - We analyzed a prospectively compiled and maintained cardiac arrest registry at a single academic medical center. Inclusion criteria are as follows: age ≥18, nontrauma arrest, and comatose after return of spontaneous circulation. We analyzed arterial blood gas data during 0 to 24 hours after the return of spontaneous circulation and determined whether patients had exposure to hypocapnia and hypercapnia (defined as PaCO₂ ≤30 mm Hg and PaCO₂ ≥50 mm Hg, respectively, based on previous literature). The primary outcome was poor neurological function at hospital discharge, defined as Cerebral Performance Category ≥3. We used multivariable logistic regression, with multiple sensitivity analyses, adjusted for factors known to predict poor outcome, to determine whether post - return of spontaneous circulation hypocapnia and hypercapnia were independent predictors of poor neurological function. Of 193 patients, 52 (27%) had hypocapnia only, 63 (33%) had hypercapnia only, 18 (9%) had both hypocapnia and hypercapnia exposure, and 60 (31%) had no exposure; 74% of patients had poor neurological outcome. Hypocapnia and hypercapnia were independently associated with poor neurological function, odds ratio 2.43 (95% confidence interval, 1.04-5.65) and 2.20 (95% confidence interval, 1.03-4.71), respectively. Conclusions: - Hypocapnia and hypercapnia were common after cardiac arrest and were independently associated with poor neurological outcome. These data suggest that PaCO₂ derangements could be potentially harmful for patients after resuscitation from cardiac arrest.