The following is a summary of “Mild Hypercapnia or Normocapnia after Out-of-Hospital Cardiac Arrest,” published in the July 2023 issue of Critical Care by Eastwood et al.

Guidelines advocate normocapnia post-out-of-hospital cardiac arrest, but mild hypercapnia could enhance neurological outcomes via increased cerebral blood flow. Researchers performed a retrospective study to compare the effects of 24 hours of mild hypercapnia versus normocapnia on neurologic outcomes and mortality in adults with coma after out-of-hospital cardiac arrest.

The study involved adults who experienced coma after cardiac arrest outside of the hospital; they randomly assigned participants to receive either mild hypercapnia (target partial pressure of arterial carbon dioxide [Paco₂], 50 to 55 mm Hg) or normocapnia (target Paco₂, 35 to 45 mm Hg) for 24 hours. The primary outcome assessed at six months was a favorable neurologic outcome (range, 1 [death] to 8 [better neurologic outcome]), and the secondary outcome was death within 6 months. Around 1,700 patients from 63 ICUs were involved; 847 received mild hypercapnia, while 853 received normocapnia. The primary outcome of a favorable neurologic outcome at 6 months occurred in 43.5% of patients in the mild hypercapnia group (332 out of 764) and 44.6% of patients in the normocapnia group (350 out of 784). Regarding mortality within 6 months after randomization, 48.2% of patients were in the mild hypercapnia group (393 out of 816), while 45.9% were in the normocapnia group (382 out of 832).

Results showed no significant difference between the two groups regarding favorable neurologic outcomes or mortality. The incidence of adverse events was also similar between the groups. [Relative risk, 0.98; 95% CI, 0.87 to 1.11; P=0.76] [Relative risk, 1.05; 95% CI, 0.94 to 1.16].

The study concluded that mild hypercapnia did not improve neurologic outcomes at 6 months in patients with coma after cardiac arrest compared to normocapnia.

Source: nejm.org/doi/full/10.1056/NEJMoa2214552