A prospective randomized clinical trial to evaluate whether 24 hours of high-flow nasal oxygen therapy after major abdominal surgery helps prevent postoperative pulmonary complications

INTERVENTION: Medical Device : This study is designed as a prospective, single‐center, randomized, controlled, open‐label, parallel‐group clinical trial. All patients will provide written informed consent after receiving a full explanation of the study before surgery. Final enrollment will be confirmed immediately after completion of surgery only if the following two conditions are met: (1) the procedure performed meets the study‐defined criteria for major abdominal surgery, and (2) the actual anesthetic duration is at least 3 hours (180 minutes). In addition, randomization will proceed only in patients who can be extubated immediately after surgery and transferred to the post‐anesthesia care unit or intensive care unit while breathing spontaneously. Eligible patients will be randomized upon arrival at the post‐anesthesia care unit or intensive care unit to either the prophylactic high‐flow nasal cannula group or the standard postoperative respiratory care group in a 1:1 ratio. Randomization will be performed using a web‐based central randomization system at the time of arrival after extubation. Patients will be allocated to the high‐flow nasal cannula group or the standard postoperative respiratory care group using block randomization with stratification according to surgical approach (open surgery versus laparoscopic or robotic surgery) and type of surgery. Because the use of high‐flow nasal cannula cannot be practically concealed, the trial will be conducted in an open‐label manner. However, key outcome assessments, including chest imaging interpretation and adjudication of atelectasis, pleural effusion, and pneumonia, will, whenever feasible, be performed by independent assessors blinded to treatment allocation. Patients in the control group will receive routine postoperative CONDITION: Diseases of the respiratory system PRIMARY OUTCOME: Incidence of clinically significant postoperative pulmonary complications (PPCs) within 7 postoperative days SECONDARY OUTCOME: All‐cause mortality within 30 days after surgery Incidence of clinically significant atelectasis within 7 postoperative days Incidence of clinically significant pleural effusion within 7 postoperative days Incidence of pneumonia within 7 postoperative days Incidence of respiratory failure within 7 postoperative days Length of hospital stay Length of ICU stay Requirement for escalation of respiratory support (non‐invasive ventilation or invasive mechanical ventilation) within 7 postoperative days INCLUSION CRITERIA: Participants will be eligible for inclusion if all of the following criteria are met: 1. Adults aged 19 years or older. 2. Patients undergoing major abdominal surgery under general anesthesia. For the purposes of this study, major abdominal surgery is defined as a procedure meeting one of the following criteria: Upper gastrointestinal surgery: total gastrectomy, distal gastrectomy, proximal gastrectomy, or surgery involving the esophagogastric junction. Lower gastrointestinal surgery: right or left hemicolectomy, low anterior resection, anterior resection, total colectomy, abdominoperineal resection, or segmental small bowel resection with anastomosis. Hepatobiliary and pancreatic surgery: hepatic resection (=1 segment), right or left hepatectomy, central hepatectomy, distal pancreatectomy, pancreaticoduodenectomy (Whipple procedure), or bile duct resection with reconstruction. Other moderate‐to‐high complexity intra‐abdominal procedures inv