During general anesthesia, particularly in patients undergoing spine surgery in the prone (face-down) position, increased intrathoracic and abdominal pressure may reduce lung compliance and promote the development of atelectasis (partial lung collapse). Atelectasis can impair intraoperative oxygenation and may increase the risk of postoperative pulmonary complications. Alveolar recruitment maneuvers (ARM) are routinely used in anesthesia practice to reopen collapsed lung regions; however, it remains unclear whether periodic application of ARM throughout surgery provides additional benefit compared with standard single-time application.

This prospective, randomized controlled clinical study aims to evaluate whether periodic alveolar recruitment maneuvers applied during elective spine surgery in the prone position reduce intraoperative atelectasis and improve respiratory mechanics compared with the standard approach of performing ARM only after positioning and before extubation. Adult patients undergoing elective spine surgery under general anesthesia will be randomly assigned to either a periodic ARM group or a standard ARM group.

Lung aeration will be assessed using lung ultrasound, a non-invasive and radiation-free bedside imaging method. The primary outcome is the incidence of intraoperative atelectasis assessed before extubation. Secondary outcomes include lung ultrasound aeration scores, respiratory mechanics parameters (such as airway pressures and compliance), oxygenation indices, and the occurrence of transient intraoperative respiratory or hemodynamic events.

The findings of this study may help optimize intraoperative ventilation strategies in prone spine surgery and contribute to improved perioperative respiratory safety.

Atelectasis frequently develops during general anesthesia due to reduced functional residual capacity, diaphragmatic displacement, and alterations in ventilation-perfusion relationships. These effects may be more pronounced during spine surgery performed in the prone position, where increased intra-abdominal and intrathoracic pressures and altered chest wall mechanics can further impair lung compliance and promote regional lung collapse. Intraoperative atelectasis has been associated with impaired oxygenation and may contribute to postoperative pulmonary complications, making its prevention an important objective in anesthetic management.

Alveolar recruitment maneuvers (ARM) are commonly used in anesthesia practice to reopen collapsed alveoli and improve lung aeration. Standard practice often involves performing a recruitment maneuver after positioning and occasionally before extubation; however, maintenance of lung aeration throughout prolonged prone procedures may be challenging. Some previous studies, including studies in pediatric populations, suggest that repeated recruitment maneuvers during surgery may provide more sustained lung aeration compared with a single application. Nevertheless, data in adult patients undergoing prone spine surgery remain limited.

This investigator-initiated, single-center randomized controlled clinical trial has been designed to evaluate the impact of periodic intraoperative alveolar recruitment maneuvers applied at predefined intraoperative intervals according to the study protocol on lung aeration and respiratory mechanics in adult patients undergoing elective spine surgery in the prone position under general anesthesia. The study primarily aims to assess lung aeration using lung ultrasound, while secondary outcomes include respiratory mechanics and perioperative physiological parameters. The periodic recruitment strategy will be compared with a standard recruitment approach used in routine anesthesia care. All ventilation maneuvers will be performed within established safety limits commonly accepted in clinical practice and will be immediately discontinued if clinically indicated. No experimental drugs, devices, or additional invasive procedures are introduced as part of the study.

Lung aeration will be evaluated using transthoracic lung ultrasound, a bedside, radiation-free, non-invasive imaging modality increasingly adopted for perioperative pulmonary assessment. Lung ultrasound allows semi-quantitative evaluation of regional aeration loss and detection of atelectasis using validated scoring systems, providing dynamic information without exposing patients to ionizing radiation. Ultrasound assessments will be performed by a trained investigator blinded to group allocation in order to minimize assessment bias.

In addition to ultrasound-based aeration assessment, intraoperative respiratory parameters such as airway pressures, lung compliance, oxygenation indices, and relevant perioperative physiological variables will be recorded to characterize the respiratory effects of different recruitment strategies. Safety monitoring will include documentation of transient hemodynamic or respiratory changes potentially associated with recruitment maneuvers.

By evaluating a practical ventilation strategy that relies on routinely used anesthetic techniques and a non-invasive monitoring tool, this study aims to provide clinically applicable data on intraoperative respiratory management in prone spine surgery. The findings may contribute to improved understanding of whether periodic recruitment maneuvers support maintenance of lung aeration and respiratory physiology compared with standard approaches.

Inclusion Criteria:

• Adults aged 18 to 65 years
• Scheduled for elective lumbar spine surgery under general anesthesia
• Surgery planned to be performed in the prone position
• Expected surgical duration of at least 2 hours
• American Society of Anesthesiologists (ASA) physical status I-II
• Ability to provide written informed consent

Exclusion Criteria:

• Body mass index (BMI) greater than 30 kg/m²
• History of thoracic surgery
• Known or suspected chronic pulmonary disease (e.g., chronic obstructive pulmonary disease, restrictive lung disease)
• Clinically significant cardiac disease
• Pregnancy or breastfeeding
• Known airway anomalies

Intraoperative surgical duration shorter than 2 hours

Refusal or inability to provide informed consent

Lung ultrasound examinations and outcome assessments will be performed by an investigator blinded to group allocation in order to minimize assessment bias. Due to the nature of the intervention, the anesthesiology team responsible for intraoperative management and recruitment maneuver application cannot be blinded. Participants will be under general anesthesia during the intervention period and therefore will not be aware of group assignment.