Pneumoperitoneum and Trendelenburg positioning during laparoscopic surgery promote atelectasis development, which has been reported in up to 90% of patients under general anesthesia and increases the risk of postoperative pulmonary complications. High-flow nasal cannula (HFNC) oxygen therapy may reduce post-extubation atelectasis through alveolar recruitment. This prospective observational cohort study aims to evaluate the role of HFNC in postoperative atelectasis monitored by lung ultrasonography (LUS) in patients undergoing elective laparoscopic surgery.

General anesthesia with laparoscopic surgery causes cephalad diaphragm displacement and reduction in functional residual capacity due to pneumoperitoneum and Trendelenburg positioning, predisposing patients to atelectasis development. Perioperative atelectasis has been reported in up to 90% of patients under general anesthesia, increasing the risk of hypoxemia, prolonged oxygen therapy, and postoperative pulmonary complications (PPCs).

High-flow nasal cannula (HFNC) oxygen therapy supports alveolar recruitment, enhances mucociliary clearance, and may reduce post-extubation atelectasis through heated and humidified gas delivery and generation of low-level positive end-expiratory pressure (PEEP). Randomized controlled trials have demonstrated that HFNC significantly reduces the incidence and severity of atelectasis assessed by LUS in robot-assisted laparoscopic rectal cancer surgery. Lung ultrasonography (LUS) has emerged as a reliable, rapid, and radiation-free method for diagnosis and monitoring of perioperative atelectasis with 87.7% sensitivity and 92.1% specificity.

This study is designed as a prospective, observational, single-center, parallel-group cohort study. No intervention or randomization will be performed. HFNC application will be left entirely to the clinician's discretion; the investigator will not be involved in the treatment process.

Patients in whom HFNC is initiated by the clinician in the post-extubation period will be defined as Group 1 (HFNC group), and patients receiving conventional oxygen therapy will be defined as Group 2 (Control group). HFNC application will be considered valid if initiated within 30 minutes of extubation.

LUS assessments will be performed by an independent investigator blinded to group assignment at four time points: T0 (preoperative), T1 (post-extubation), T2 (30th minute in the recovery unit), and T3 (discharge from the recovery unit). An additional LUS assessment is planned at postoperative 24 hours (T4). The Monastesse modified LUS score will be used at each assessment, evaluating 12 thoracic regions (6 segments per hemithorax along parasternal, anterior axillary, and posterior axillary lines), with a total LUS score ranging from 0 to 36 points.

HFNC parameters (flow rate, FiO₂, duration) and intraoperative variables (type and duration of surgery, anesthesia duration, insufflation duration, pneumoperitoneum pressure, Trendelenburg angle, total fluid intake, urine output) as well as postoperative variables (minimum SpO₂ in the recovery unit, length of hospital stay) will be considered as potential confounding factors in the statistical analysis.

Inclusion Criteria:

• Adult patients aged 18 years and older
• Patients scheduled for elective laparoscopic surgery (general surgery, urology, gynecology)
• Patients undergoing mechanical ventilation under general anesthesia
• ASA physical status I-III
• Patients providing written informed consent

Exclusion Criteria:

• Severe or uncontrolled chronic obstructive pulmonary disease, asthma, or other chronic pulmonary diseases
• Patients with atelectasis or pleural effusion detected on preoperative lung ultrasonography
• Patients requiring intraoperative recruitment maneuver
• ASA physical status IV or above
• Patients receiving spinal or epidural anesthesia
• Cases requiring conversion to laparoscopy or laparotomy
• Patients refusing to participate

Adult patients aged 18-75 years scheduled for elective laparoscopic surgery (general surgery, urology, and gynecology) under general anesthesia.