In this randomized-controlled trial the investigators will examine the effect of oxygen supplementation on the recovery of breathing for 90 minutes in the immediate post-anesthesia period starting from extubation of the trachea.

In a pilot randomized-controlled trial (NCT04723433) the investigators found that hyperoxia, compared with standard O2 supplementation, enhanced ventilation, as estimated by the fraction of time at a transcutaneous PCO2 (TcPCO2) > 45 mmHg.

More specifically, patients treated with hyperoxia (O2 titrated to: SpO2 > 96%, N=10; Liberal O2) for 90 minutes post-anesthesia, spent 61.2% of the time at TcPCO2 > 45 mmHg, compared with 80.6% of the time in those receiving standard O2 supplementation (O2 titrated to: SpO2 between 90-94%, N=9; Conservative O2 - between-group difference of 19.4% (95% CI: -18.7% to 57.6%), ANCOVA adjusted P = 0.140]. Results were consistent across the 90-min monitoring period. With an observed effect size of 0.73, it was estimated that 30 participants per group are required, to demonstrate this difference with a power of 80% at a two-sided alpha of 5%.

In the present confirmative randomized controlled trial, the investigators plan to estimate and compare the cumulative segment of time during which the transcutaneous partial pressure of carbon dioxide will exceed an upper limit of 45 mmHg (i.e., TcPCO2 > 45 mmHg) for the 90-min-long post-anesthesia period, between the conventional (titrated to an oxygen saturation > 96%) and the conservative (titrated to O2 saturation 90-94%) O2 supplementation interventions.

Hypothesis: Conservative use of O2 (titrated to an SpO2: 90 - 94%), will be associated with more hypoventilation (i.e., more time spent with an TcPCO2 > 45 mmHg) during recovery from general anesthesia, compared to liberal O2 supplementation (SpO2 > 96%).

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status I-III
• Body mass index (BMI) less than 40 kg/m2
• Scheduled to undergo robotic-assisted radical laparoscopic nephrectomy or prostatectomy.

Exclusion Criteria:

• Patients with a diagnosis of chronic obstructive pulmonary disorder (COPD), severe neurological, cardiopulmonary, psychiatric, or untreated thyroid disorder
• Chronic pain condition that is being treated with opioids
• Patients with a hematocrit lower than 30% at the end of surgery, or those with an excessive blood loss, requiring transfusion of blood products during surgery.

Patients will be blinded to the received treatment. The investigators, who will monitor the patients and collect the data in the PACU, will be blinded to the primary outcome, but not to the received treatment.