Comparative Evaluation of Central Venous Oxygen Saturation, Carbon Dioxide Venous Arterial Gradient, and Lactate Levels as Markers of Tissue Perfusion After Cardiac Surgery: A Prospective Exploratory Observational Study

Objective: This study aims to identify which markers of tissue hypoperfusion - specifically lactate levels, central venous oxygen saturation (ScvO2), and venous arterial carbon dioxide gradient (CO2 gradient) - have the highest sensitivity and specificity in predicting the discharge of postoperative cardiac surgical patients from the ICU within 48 hours. This is an exploratory, hypothesis-generating investigation. Methods: Prospective observational study involving 100 patients in the Surgical ICU at InCor-HCFMUSP undergoing cardiac surgery with cardiopulmonary bypass. Perfusion markers were assessed at ICU admission and 24 hours post-admission. Results: ScvO2 at 24 hours was the only marker significantly associated with ICU discharge (OR=1.096; 95% CI=1.020-1.180; p=0.012). Formal DeLong's test confirmed ScvO2 had significantly superior discriminatory performance compared to lactate (AUC 0.661 vs. 0.428; p=0.004). Lactato and CO2 gap showed no significant associations. Conclusions: In this exploratory cohort, ScvO2 at 24 hours post-admission showed a statistically significant association with early ICU discharge and superior discriminatory performance compared to lactate. These findings are hypothesis-generating and require prospective validation before clinical recommendations can be made.