What intervention is most likely to increase a patient's mixed venous oxygen saturation during general anesthesia?

Inducing general anesthesia with a muscle relaxant is the most likely intervention to increase a patient’s mixed venous oxygen saturation during general anesthesia. When general anesthesia is induced, muscle relaxants cause relaxation of the muscles, facilitating controlled ventilation and improved respiratory mechanics. This allows for more effective oxygenation, as the patient is typically placed on controlled ventilation, ensuring adequate ventilation and eliminating any potential airway obstructions.

Improved ventilation directly enhances the oxygenation of blood and can contribute to an increase in mixed venous oxygen saturation since the returning blood from systemic circulation will have higher oxygen content.

Other options do not support this goal: the administration of a beta-blocker could potentially decrease cardiac output, impacting oxygen delivery instead of enhancing it. Reducing the FiO2 would lead to lower oxygen availability, which could decrease mixed venous oxygen saturation. Lastly, removing units of blood during acute normovolemic hemodilution would decrease the overall volume and could compromise oxygen delivery, impacting mixed venous oxygen saturation negatively.