Association between venous to arterial carbon dioxide tension gap and clinical outcome in cardiac surgery patients: A systematic review and meta-analysis.

BackgroundCardiac surgery is associated with increased risk of major adverse outcomes. Venous to arterial carbon dioxide tension gap (Pv-aCO₂ gap) showed significant prognostic value of non-cardiac surgery, while their prognostic value after cardiopulmonary bypass (CPB) remains controversial.MethodsWe conducted a systematic research of PubMed, MEDLINE, EMBASE and Web of science electronic database and ClinicalTrials.gov to analysis the association between high Pv-aCO₂ gap and adverse outcomes in adult cardiac surgery patients. Random effect model was used to pool data.ResultsEight studies (n = 2136 patients) were enrolled. High Pv-aCO₂ gap was mainly defined as Pv-aCO₂ ≥ 6-8 mmHg. In cardiac surgery, high Pv-aCO₂ gap was not associated with increased hospital mortality (odds ratio, 0.63; 95% CI, 0.17-2.32; p = 0.49)), but was related with higher ICU mortality (odds ratio, 5.27; 95% CI, 2.31-12.00; p < 0.001), higher incidence of major complications (p < 0.05), longer ICU length of stay (p = 0.03) and prolonged ventilation time in the ICU (p < 0.001). Moreover, high Pv-aCO₂ gap was linked to postoperative lower cardiac index (p < 0.01) and lower ScvO₂ (p < 0.001). Interesting, high Pv-aCO₂ gap was not associated with increased postoperative lactate level and longer hospital length of stay.ConclusionAn elevated Pv-aCO₂ gap seems to be associated with adverse outcomes in very short time and indicates tissue hypoperfusion rather than tissue hypoxia. Therefore, interventions aiming at normalizing Pv-aCO₂ gap may potentially improve clinical outcomes, while further validation is required.