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NCT Number: NCT07041567

Low-Flow Anesthesia and Perioperative Atelectasis in Laparoscopic Bariatric Surgery

The goal of this clinical trial is to learn whether low-flow anesthesia reduces perioperative atelectasis compared to normal-flow anesthesia in adults undergoing laparoscopic bariatric surgery. The main questions it aims to answer are:

Does low-flow anesthesia result in a smaller increase in lung ultrasound score from baseline to postoperative hour 1? Does low-flow anesthesia result in better preservation of pulmonary function at postoperative hour 48?

Researchers will compare low-flow anesthesia (fresh gas flow 0.5 L/min) to normal-flow anesthesia (fresh gas flow 2 L/min) to see if low-flow anesthesia reduces the extent of perioperative atelectasis as measured by lung ultrasound.

Participants will:

Be randomly assigned to receive either low-flow or normal-flow inhalational anesthesia with sevoflurane during surgery Undergo lung ultrasound assessments before surgery and at postoperative hours 1 and 24 Undergo spirometric testing one day before surgery and at postoperative hour 48

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Key information

Conditions

Atelectasis Bariatric Surgery Low Flow Anesthesia Lung Diseases Pulmonary Atelectasis Pulmonary Complications Respiratory Tract Diseases Ultrasonography

Age range

18 year–65 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Göztepe Prof.Dr. Süleyman Yalçın Şehir Hastanesi

Istanbul, Goztepe, 34000, Turkey (Türkiye)

About this study

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.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

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

  1. Change in modified Lung Ultrasound Score from baseline to postoperative hour 1 (ΔmLUSS₁ₕ)

    Time frame: 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

  1. Change in modified Lung Ultrasound Score from baseline to postoperative hour 24 (ΔmLUSS₂₄ₕ)

    Time frame: 24 hours postoperatively

    Between-group difference in the change in mLUSS from preoperative baseline to postoperative hour 24

  2. Changes in spirometric parameters from baseline to postoperative hour 48

    Time frame: 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.

  3. Intraoperative hemodynamic event incidences

    Time frame: Intraoperatively

    Incidences of hypotension, hypertension, bradycardia, tachycardia, oxygen desaturation, and hypercapnia during surgery, compared between groups.

Sponsors and collaborators

Lead sponsor

Istanbul University

Other

Registry information

Official study title

Effect of Low-Flow Anesthesia on Perioperative Atelectasis in Patients Undergoing Laparoscopic Bariatric Surgery: A Randomized Controlled Trial

Important dates

Study start
2026
Primary completion
2026
Study completion
2026
First posted
Jun 27, 2025
Registry last updated
May 20, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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