HFNC for Postoperative Atelectasis After 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.

• Incidence of Significant Atelectasis [Time frame: T0: preoperative; T1: 5th minute after extubation; T2: 30th minute in the recovery unit; T3: discharge from the recovery unit]
• Minimum SpO₂ in the Post-Anesthesia Care Unit (PACU) [Time frame: From extubation to PACU discharge, up to 2 hours]
• Incidence of Hypoxemia [Time frame: From extubation to PACU discharge, up to 2 hours]
• Incidence of Severe Hypoxemia [Time frame: From extubation to PACU discharge, up to 2 hours]
• Postoperative Complications [Time frame: From surgery to hospital discharge, up to 7 days]