IL6 and respiratory depression: The secondary outcomes include QoR-40 score on POD 2 and POD 3, levels of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), pain scores at rest and while coughing, time to extubate, length of patients' stay in the post-anesthesia care unit, awakening time, ramsay sedation score on awakening, adverse events (postoperative symptoms such as nausea, vomiting, headache, respiratory depression, hypoxemia).