Effect of hypercapnia on neurologic outcomes after cardiac arrest: A systematic review and meta-analysis

Brain injury often occurs after cardiac arrest, and the regulation of PaCO₂ plays a crucial role in mediating cerebral blood flow. The current guidelines recommend maintaining normocapnia through ventilation in post-arrest patients. However, the effects of hypercapnia on neurological outcomes remain controversial. To address this issue, we undertook a meta-analysis to compare the effects of hypercapnia and normocapnia on the neurological outcomes in patients with cardiac arrest.

As of December 5, 2023, we conducted a search on eligible studies, including EMBASE, PubMed, and WOS databases. Our primary outcome of interest was a good neurological outcome, and two authors independently screened the studies and extracted relevant data. For analysis, a fixed effects model was used when the I² values were less than 50 %, whereas a random effects model was used for higher I² values.

From the 2137 studies initially identified, seven studies involving 2770 patients were ultimately included. Compared with normocapnia, hypercapnia significantly improved the neurological outcomes of patients with cardiac arrest (OR 0.73; 95 % CI 0.56-0.96; P = 0.02). According to the subgroup analysis, the hypercapnic group achieved better neurological outcomes in the short-term than did the normocapnia group (OR 0.61; 95 % CI 0.42-0.88; P = 0.008), whereas no significant difference was observed in long-term (OR 0.91; 95 % CI 0.76-1.10; P = 0.35). Moreover, there was no significant difference in mortality between the two groups (OR 1.03; 95 % CI 0.65-1.63; P = 0.91).

Our results suggest that hypercapnia is associated with a good neurological prognosis, especially in the short-term setting. However, further well-powered randomized controlled trials are necessary to confirm the optimal PaCO₂ targets.

CRD42023457027. Registered 3 September 2023.