A systematic review and meta-analysis of the association between arterial carbon dioxide tension and outcomes after cardiac arrest.

Abstract

Arterial carbon dioxide tension (PaCO₂) abnormalities are common after cardiac arrest (CA). Maintaining a normal PaCO₂ makes physiological sense and is recommended as a therapeutic target after CA, but few studies have examined the association between PaCO₂ and patient outcomes. This systematic review and meta-analysis aimed to assess the effect of a low or high PaCO₂ on patient outcomes after CA. We searched MEDLINE, EMBASE, CINAHL and Cochrane CENTRAL, for studies that evaluated the association between PaCO₂ and outcomes after CA. The primary outcome was hospital survival. Secondary outcomes included neurological status at the end of each study's follow up period, hospital discharge destination and 30-day survival. Meta-analysis was conducted if statistical heterogeneity was low. The systematic review included nine studies; eight provided sufficient quantitative data for meta-analysis. Using PaCO₂ cut-points of <35mmHg and >45mmHg to define hypo- and hypercarbia, normocarbia was associated with increased hospital survival (odds ratio [OR] 1.30, 95% confidence interval [CI] 1.23, 1.38). Normocarbia was also associated with a good neurological outcome (cerebral performance category score 1 or 2) compared to hypercarbia (OR 1.69, 95% CI 1.13, 2.51) when the analysis also included an additional study with a slightly different definition for normocarbia (PaCO₂ 30-50mmHg). From the limited data it appears PaCO₂ has an important U-shape association with survival and outcomes after CA, consistent with international resuscitation guidelines' recommendation that normocarbia be targeted during post-resuscitation care.