High-Flow Nasal Oxygen versus Mechanical Ventilation Through a Laryngeal Mask During General Anesthesia Without Muscle Paralysis: A Randomized Clinical Trial.

BACKGROUND Apneic oxygenation with high-flow nasal oxygen is a novel intraoperative respiratory support strategy for patients undergoing general anesthesia, but data about its clinical effects are scarce. We conducted a randomized trial to assess whether high-flow nasal oxygen is noninferior to mechanical ventilation through a laryngeal mask in terms of success rate of intraoperative respiratory support among patients undergoing a 30-minute general anesthesia session. METHODS Single-center, randomized, noninferiority trial conducted in Italy between May 2022 and June 2023 and involving American Society of Anesthesiologists class I and II patients undergoing general anesthesia for operative hysteroscopy. Participants were randomized to receive laryngeal mask ventilation (volume-controlled ventilation to obtain end-tidal carbon dioxide between 35 and 45 mm Hg, inhaled oxygen fraction to achieve peripheral oxygen saturation greater than 95%) or high-flow nasal oxygen (70 L per minute, inhaled oxygen fraction of 100%) for intraoperative respiratory support. Patients received general anesthesia with propofol target-controlled infusion without neuromuscular blockade. Primary outcome was intraoperative respiratory support success rate, which was defined as peripheral oxygen saturation greater than 94% and transcutaneous carbon dioxide lower than 65 mm Hg with no need for rescue airway interventions for the entire procedure. Secondary outcomes included the rate of airway-related complications (including need for bag-mask or laryngeal mask ventilation, or tracheal intubation), postoperative respiratory symptoms, and postoperative dyspnea. RESULTS All 180 patients who were randomized completed the trial (90 patients in each group). Median [interquartile range] anesthesia duration was 25 [20-36] minutes in high-flow group and 32 minutes [27-44] in the laryngeal mask group. Intraoperative respiratory support was successful in 89 patients (99%) in both groups (absolute difference 0, unilateral 95% confidence interval, 3%, noninferiority P < .001). Incidence of postoperative respiratory symptoms was significantly lower in high-flow versus laryngeal mask group (2% vs 19%, P < .001), while airway-related complications and postoperative dyspnea were not different. Intraoperative transcutaneous carbon dioxide was significantly higher in high-flow group, with 43% of patients showing values greater than 55 mm Hg. CONCLUSIONS High-flow nasal oxygen is noninferior to laryngeal mask ventilation for intraoperative respiratory support during 30-minute general anesthesia without muscle paralysis. The risk of hypercarbia warrants careful patient selection and monitoring.