Introduction: Venous oxygen saturation is a metabolic variable that complements the information provided by hemodynamic parameters and globally evaluates the oxygen delivery and consumption by bodily tissues.Its precise values under general anesthesia are unknown, and constitutes an area of great interest for research.Objectives: To evaluate the effect of general anesthesia on Central Venous Oxygen Saturation (SvcO 2 ) in patients undergoing major surgical procedures.Methods: Aquasi-experimental before-after study in which central venous oxygen saturation (SvcO 2 ) values were obtained by gasometry and compared before the induction of anesthesia and 30 minutes after initiation of ventilatory support.The study included 111 patients undergoing major surgery under general anesthesia, grouped into 3 age groups.Results: There is a statistically significant increase in SvcO 2 from baseline values of 66.29% to 76.89% (15.99%, p<0.05) in patients under general anesthesia.Conclusion: SvcO 2 increases significantly in patients of all ages under general anesthesia.The aforementioned results are important when re-evaluating the pre-established reference values in the various clinical settings requiring general anesthesia.