Effect of Intravenous S-ketamine on Opioid Consumption

Patients in the low-dose ketamine group will receive a bolus of 0.5 mg/kg S-ketamine in saline, followed by continuous infusion of 2 μg/kg/min S-ketamine in saline until 30 min prior to the end of the surgery.

Patients in the placebo group will receive a bolus of 0.9% saline, followed by continuous infusion of 0.9% saline until 30 min prior to the end of the surgery.

Patients in the high-dose ketamine group will receive a bolus of 0.5 mg/kg S-ketamine in saline, followed by continuous infusion of 4 μg/kg/min S-ketamine in saline until 30 min prior to the end of the surgery.