Low-Flow Anesthesia and Perioperative Atelectasis in Laparoscopic Bariatric Surgery

This prospective, single-center, randomized controlled trial investigates the effect of low-flow anesthesia on perioperative atelectasis in patients undergoing elective laparoscopic sleeve gastrectomy. Morbidly obese patients are at increased risk of perioperative atelectasis due to reduced functional residual capacity, diaphragmatic elevation, and the additional physiological burden of pneumoperitoneum and reverse Trendelenburg positioning during laparoscopic surgery.

Eligible patients are randomized in a 1:1 ratio to one of two groups. In the normal-flow group (Group N), anesthesia is maintained with sevoflurane at a fresh gas flow of 2 L/min. In the low-flow group (Group D), anesthesia is initiated at 4 L/min to achieve rapid equilibration and then reduced to 0.5 L/min once 1.0 minimum alveolar concentration (MAC) is reached. All patients receive standardized lung-protective mechanical ventilation and an identical anesthetic protocol otherwise.

Atelectasis is quantified using the modified Lung Ultrasound Scoring System (mLUSS), in which each of 12 lung zones is scored 0-3 based on aeration loss, yielding a total score of 0-36. Assessments are performed preoperatively, at postoperative hour 1, and at postoperative hour 24 by a single investigator blinded to group allocation. Pulmonary function tests (FVC, FEV₁, FEV₁/FVC, PEF, FEF₂₅-₇₅) are performed preoperatively and at postoperative hour 48 by a separate blinded investigator.

Secondary outcomes include changes in spirometric parameters, intraoperative hemodynamic event incidences, mean intraoperative FiO₂ and plateau pressure, sevoflurane and remifentanil consumption, postoperative nausea and vomiting incidence, and postoperative analgesic requirements.

• Sevoflurane with normal-flow anesthesia (Drug): Sevoflurane is delivered via inhalation with a fresh gas flow of 2 L/min throughout surgery. Vaporizer is set to 2.5%.
• Sevoflurane with low-flow anesthesia (Drug): Sevoflurane is delivered via inhalation. Anesthesia is initiated at FGF 4 L/min with vaporizer at 6% for rapid equilibration. Once end-tidal sevoflurane reaches 1.0 MAC, FGF is reduced to 0.5 L/min and titrated to maintain 1.0 MAC.

Primary outcomes

• Change in modified Lung Ultrasound Score from baseline to postoperative hour 1 (ΔmLUSS₁ₕ) [1 hour after arrival to the post-anesthesia care unit (PACU)]: The mLUSS is calculated by scoring 12 lung zones (0-3 per zone) based on aeration loss on lung ultrasound, yielding a total score of 0-36. The primary outcome is the between-group difference in the change from preoperative baseline to postoperative hour 1.

Secondary outcomes

• Change in modified Lung Ultrasound Score from baseline to postoperative hour 24 (ΔmLUSS₂₄ₕ) [24 hours postoperatively]: Between-group difference in the change in mLUSS from preoperative baseline to postoperative hour 24
• Changes in spirometric parameters from baseline to postoperative hour 48 [48 hours postoperatively]: Between-group differences in the change in FVC, FEV₁, FEV₁/FVC, PEF, and FEF₂₅-₇₅ from preoperative baseline to postoperative hour 48.
• Intraoperative hemodynamic event incidences [Intraoperatively]: Incidences of hypotension, hypertension, bradycardia, tachycardia, oxygen desaturation, and hypercapnia during surgery, compared between groups.

Sex: All, ages: 18 Years to 65 Years

Inclusion Criteria:

Age 18-65 years ASA physical status III Scheduled for elective laparoscopic sleeve gastrectomy under general anesthesia Able to provide written informed consent and cooperate with study procedures

Exclusion Criteria:

Severe respiratory comorbidities (advanced COPD, restrictive lung disease, or severe obstructive sleep apnea syndrome) Advanced heart failure (ejection fraction < 20%) Chronic renal failure Hepatic insufficiency Uncontrolled diabetes mellitus Uncontrolled hypertension Limited capacity to cooperate with study procedures