Evaluation of the Effects of Intraoperative Ventilation Modes on Perioperative Atelectasis

Evaluation of the Effects of Intraoperative Ventilation Modes on Perioperative Atelectasis in Patients Undergoing Hysterectomy by Lung Ultrasonography

In hysterectomy surgeries, due to factors such as the abdominal nature of the procedure, prolonged operative duration, and the use of the head-down (Trendelenburg) position during surgery, a lobe or a specific region of the lungs may collapse and fail to fill with air in the postoperative period. This condition is referred to as atelectasis.

In this study, the investigators aimed to evaluate the effects of ventilation modes used in the operating room on the development of postoperative atelectasis using lung ultrasonography.

Study Overview

• Status: Completed
• Conditions: Atelectasis, Postoperative Pulmonary

Detailed Description

Postoperative pulmonary complications (such as atelectasis, pneumonia, pulmonary embolism, pleural effusion, pulmonary edema, and pneumothorax) are clinically significant because hospital stay is prolonged and morbidity and mortality are increased. Atelectasis is one of the most common respiratory complications in the perioperative period and occurs in 80-100% of patients undergoing general anesthesia. Anesthesia may lead to alveolar inhomogeneity, and the use of positive pressure ventilation may cause lung injury through mechanisms such as atelectotrauma, barotrauma, and biotrauma. Therefore, identifying the relationship between routine perioperative practices and the development of atelectasis may help guide the development of preventive strategies. Ventilator-induced lung injury (VILI) arises from the interaction between the energy delivered by the ventilator to the lung tissue and the tissue's response to this energy. Ventilator-associated lung injury occurring in patients receiving mechanical ventilation significantly increases morbidity and mortality. In recent years, numerous studies have focused on improving standard ventilation strategies-such as reducing tidal volume and adjusting positive end-expiratory pressure (PEEP)-to reduce the risk of VILI. However, VILI rates remain high and continue to contribute to postoperative pulmonary complications as well as complications in intensive care patients. One of the principal challenges of mechanical ventilation is the inability to accurately assess patient-specific lung mechanics using routinely monitored parameters. The lung characteristics predisposing to VILI are particularly dependent on the degree of pulmonary edema. Edema promotes atelectasis, increases inhomogeneity, elevates mechanical stress, and leads to cyclic opening and closing of alveoli. Ventilator-induced lung injury results from the interaction between mechanical power and the ventilated lung parenchyma. Tidal volume, ΔPaw (difference in plateau airway pressure), peak airway pressure, respiratory rate (RR), flow rate, and positive end-expiratory pressure (PEEP) are components of this interaction, each contributing to mechanical power in different ways. Factors affecting the development of atelectasis include the type, location, and duration of surgery, as well as patient positioning. Hysterectomy procedures are considered a high-risk group for postoperative atelectasis because they involve abdominal surgery, prolonged operative times, and the use of the Trendelenburg position. Anesthesia-related atelectasis is often too small to be detected on conventional chest radiographs. Comparative studies using computed tomography (CT) or magnetic resonance imaging (MRI) have demonstrated that lung ultrasonography can reliably detect anesthesia-related atelectasis with approximately 90% sensitivity, specificity, and diagnostic accuracy. Lung ultrasonography is therefore recommended for the diagnosis of anesthesia-related atelectasis and for monitoring respiratory complications. Flow-controlled ventilation (FCV) is a ventilation mode in which a constant low flow is applied during both inspiration and expiration. In this technique, airway pressure increases linearly during inspiration and decreases linearly during expiration. The applied flow is adjusted to maintain normocapnia (normal arterial carbon dioxide levels), and the inspiration-to-expiration (I:E) ratio is set at 1:1. This technique represents an innovative approach in mechanical ventilation. With constant flow and direct measurement of tracheal pressure, individualized lung mechanics can be assessed, which is not possible with conventional ventilation modes in which flow is variable and tracheal pressure cannot be directly monitored. Flow-controlled ventilation allows accurate calculation of dynamic compliance, enabling precise adjustment of positive end-expiratory pressure and peak inspiratory pressure (Ppeak). Thus, ventilation can be delivered within the lower and upper inflection points of the pressure-volume curve, tailored to individual lung mechanics. In pressure-controlled ventilation (PCV), peak airway pressure is controlled, and mandatory respiratory rate and inspiratory time are set. Once the preset pressure is reached, gas flow ceases; however, expiration does not begin until the preset inspiratory time has elapsed. In volume-controlled ventilation (VCV), a fixed tidal volume is delivered using a user-defined flow rate and inspiratory time. Airway pressure may vary, and excessive pressure may lead to barotrauma. In this study, the investigators aimed to evaluate the effects of flow-controlled ventilation, volume-controlled ventilation, and pressure-controlled ventilation modes used in the operating room on the development of postoperative atelectasis using lung ultrasonography. Following approval numbered 2024/241 by the Scientific Research Ethics Committee of Sancaktepe Şehit Prof. Dr. İlhan Varank Training and Research Hospital, patients scheduled for elective hysterectomy who met the inclusion criteria were screened. Patients who provided written informed consent after receiving detailed information about the study were included. Age, American Society of Anesthesiologists Physical Status Classification (ASA score), body mass index (BMI), and duration of surgery were recorded. Due to the observational nature of the study, lung ultrasonographic evaluation-considered a routine component of the pre-anesthesia assessment in the clinic-was performed, and lung ultrasound scores were recorded. After each participant was positioned on the operating table, standard anesthesia monitoring was applied, including heart rate (HR), electrocardiography (ECG), noninvasive arterial blood pressure monitoring, mean arterial pressure (MAP), peripheral oxygen saturation (SpO₂), and processed electroencephalography measured by the bispectral index (BIS). These parameters were recorded. Adequate surgical depth of anesthesia was achieved using propofol-remifentanil infusion guided by processed electroencephalography monitoring. After induction and adjustment of the mechanical ventilator by the responsible anesthesiologist, the observer recorded vital signs (SpO₂, HR, arterial pressure, processed electroencephalography), ventilation mode, peak airway pressure (Ppeak), positive end-expiratory pressure, plateau pressure, tidal volume, respiratory rate (f), end-tidal carbon dioxide (EtCO₂), fraction of inspired oxygen (FiO₂), flow rate, and inspiration-to-expiration ratio. Measurements were recorded at the following time points: preoperatively, after induction, before and after pneumoperitoneum, before and after positioning, and at 30-minute intervals thereafter. Arterial blood gas analysis was performed preoperatively and in the post-anesthesia care unit (PACU). Using vital signs, blood gas analysis, and mechanical ventilator parameters, heart rate, mean arterial pressure, peripheral oxygen saturation (SpO₂), mechanical power, lung compliance, end-tidal carbon dioxide (EtCO₂), partial pressure of carbon dioxide (pCO₂), partial pressure of oxygen (pO₂), the ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO₂/FiO₂ ratio), bispectral index (BIS), and intra-abdominal pressure were evaluated. For postoperative analgesia, techniques and medications selected by the responsible anesthesiologist, including intravenous drugs and neuraxial techniques, were recorded. In accordance with routine clinical practice, patients were transferred from the post-anesthesia care unit to the ward when the Visual Analog Scale (VAS) score was ≤3 and the Modified Aldrete Score was ≥9. Lung ultrasonographic evaluations were performed at the time of transfer and at postoperative 2 and 24 hours. Changes in lung ultrasound scores relative to preoperative values were assessed. Pain scores were recorded using the Visual Analog Scale at postoperative 2, 6, 12, and 24 hours. The statistical power of the study was expressed as 1-β (β = type II error probability), and a power of 80% was considered adequate. To achieve 80% power at a significance level of α = 0.05, a minimum of 22 patients per group (66 patients in total) was required. Considering the possibility of data loss, the study was planned to include 78 patients.

• Study Type: Observational
• Enrollment (Actual): 78

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Istanbul
    • Sancaktepe, Istanbul, Turkey (Türkiye), 34785
      • Sehit Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Patients meet eligibility criteria and will undergone histerectomy surgery from 15/09/2024 to 15/09/2025 in Sehit Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital

Description

Inclusion Criteria

Patients aged 45 years and older scheduled for hysterectomy surgery with an expected operative duration of more than 2 hours

Patients classified as American Society of Anesthesiologists (ASA) Physical Status Class I, II, or III

Patients for whom planned total intravenous anesthesia was preferred

Exclusion Criteria

Patients younger than 45 years

Patients planned for postoperative intensive care unit monitoring

Patients unable to provide written informed consent

Patients classified as American Society of Anesthesiologists Physical Status Class IV or higher

Patients with a body mass index (BMI) greater than 35

Patients who did not consent to participate in the study

Patients with neuromuscular diseases

Patients with uncontrolled asthma

Patients with chronic obstructive pulmonary disease (COPD), Global Initiative for Chronic Obstructive Lung Disease (GOLD) Class IV

Patients with scoliosis

Patients with a history of pulmonary resection

Patients with chest wall deformities

Patients with a history of spontaneous pneumothorax

Patients for whom inhalational anesthesia was preferred

Study Plan

How is the study designed?

Number of groups / cohorts

3

Cohorts and Interventions

Group / Cohort
Flow-Controlled Ventilation (FCV); Patients were divided into three groups according to the type of ventilation used. The group that received flow-controlled ventilation was designated as the FCV group. In the FCV group, a constant flow is applied during both inspiration and expiration. In all three groups, lung ultrasonographic evaluation was performed preoperatively and up to 24 hours postoperatively, and the lung ultrasound scores were determined. Vital signs, ventilation parameters, blood gas analysis, and pain scores were also recorded at specific time intervals.
Pressure-Controlled Ventilation (PCV); Patients were divided into three groups according to the type of ventilation used. The group that received pressure-controlled ventilation was designated as the PCV group. In the PCV group, the peak airway pressure is controlled. The mandatory respiratory rate and inspiratory time are also adjusted. In all three groups, lung ultrasonographic evaluation was performed preoperatively and up to 24 hours postoperatively, and the lung ultrasound scores were determined. Vital signs, ventilation parameters, blood gas analysis, and pain scores were also recorded at specific time intervals.
Volume-Controlled Ventilation (VCV); Patients were divided into three groups according to the ventilation mode used. The group receiving volume-controlled ventilation (VCV) was designated as the VCV group. In the VCV group, a specific tidal volume (Vt) was achieved by maintaining a constant flow rate and inspiratory time set on the ventilator, while airway pressure was allowed to vary. In all three groups, lung ultrasonographic evaluation was performed preoperatively and up to 24 hours postoperatively, and lung ultrasound scores were determined. Vital signs, ventilation parameters, blood gas analysis results, and pain scores were recorded at predefined time intervals.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Lung Ultrasound Score (ΔLUS) From Preoperative Baseline to 24 Hours Postoperatively	Perioperative atelectasis was assessed as the change in Lung Ultrasound Score (ΔLUS) from preoperative baseline to 24 hours postoperatively. Lung aeration was evaluated using a standardized 12-region scoring system (0-36 scores on a scale). ΔLUS was calculated as postoperative LUS at 24 hours minus preoperative baseline LUS. Higher values indicate greater loss of aeration.	Preoperative baseline and 24 hours postoperatively

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Mechanical Power During Intraoperative Ventilation	Mechanical power calculated from ventilator parameters at predefined intraoperative time points.	Intraoperative period
Arterial Oxygen Partial Pressure (PaO₂)	PaO₂ measured by arterial blood gas analysis at preoperative baseline and at the time of discharge from the Post-Anesthesia Care Unit (PACU).	Preoperative and at the time of transfer from the Post-Anesthesia Care Unit (PACU) to the ward (PACU discharge).
PaO₂/FiO₂ Ratio	PaO₂/FiO₂ ratio was calculated from arterial blood gas analysis using PaO₂ and the fraction of inspired oxygen (FiO₂) at preoperative baseline and at the time of discharge from the Post-Anesthesia Care Unit (PACU).	Preoperative and at the time of transfer from the Post-Anesthesia Care Unit (PACU) to the ward (PACU discharge).

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Lung Ultrasound Score (ΔLUS) During Early Postoperative Period	Change in Lung Ultrasound Score (ΔLUS) calculated as postoperative LUS minus preoperative baseline LUS. Lung aeration was assessed using a standardized 12-region scoring system (0-36 points). Positive values indicate increased loss of aeration. Measurements were obtained at PACU discharge and at postoperative 2 hours.	Preoperative baseline, at discharge from the Post-Anesthesia Care Unit (PACU), and at 2 hours postoperatively

Collaborators and Investigators

• Sponsor: Sehit Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital

Publications and helpful links

General Publications

• Mazo V, Sabate S, Canet J, Gallart L, de Abreu MG, Belda J, Langeron O, Hoeft A, Pelosi P. Prospective external validation of a predictive score for postoperative pulmonary complications. Anesthesiology. 2014 Aug;121(2):219-31. doi: 10.1097/ALN.0000000000000334.
• Cressoni M, Gotti M, Chiurazzi C, Massari D, Algieri I, Amini M, Cammaroto A, Brioni M, Montaruli C, Nikolla K, Guanziroli M, Dondossola D, Gatti S, Valerio V, Vergani GL, Pugni P, Cadringher P, Gagliano N, Gattinoni L. Mechanical Power and Development of Ventilator-induced Lung Injury. Anesthesiology. 2016 May;124(5):1100-8. doi: 10.1097/ALN.0000000000001056.
• O'Gara B, Talmor D. Perioperative lung protective ventilation. BMJ. 2018 Sep 10;362:k3030. doi: 10.1136/bmj.k3030.
• Barnes T, van Asseldonk D, Enk D. Minimisation of dissipated energy in the airways during mechanical ventilation by using constant inspiratory and expiratory flows - Flow-controlled ventilation (FCV). Med Hypotheses. 2018 Dec;121:167-176. doi: 10.1016/j.mehy.2018.09.038. Epub 2018 Sep 24.
• Beitler JR, Malhotra A, Thompson BT. Ventilator-induced Lung Injury. Clin Chest Med. 2016 Dec;37(4):633-646. doi: 10.1016/j.ccm.2016.07.004. Epub 2016 Oct 14.
• Gertler R. Respiratory Mechanics. Anesthesiol Clin. 2021 Sep;39(3):415-440. doi: 10.1016/j.anclin.2021.04.003.
• Gattinoni L, Pelosi P, Crotti S, Valenza F. Effects of positive end-expiratory pressure on regional distribution of tidal volume and recruitment in adult respiratory distress syndrome. Am J Respir Crit Care Med. 1995 Jun;151(6):1807-14. doi: 10.1164/ajrccm.151.6.7767524.
• Protti A, Maraffi T, Milesi M, Votta E, Santini A, Pugni P, Andreis DT, Nicosia F, Zannin E, Gatti S, Vaira V, Ferrero S, Gattinoni L. Role of Strain Rate in the Pathogenesis of Ventilator-Induced Lung Edema. Crit Care Med. 2016 Sep;44(9):e838-45. doi: 10.1097/CCM.0000000000001718.
• Ball L, Hemmes SNT, Serpa Neto A, Bluth T, Canet J, Hiesmayr M, Hollmann MW, Mills GH, Vidal Melo MF, Putensen C, Schmid W, Severgnini P, Wrigge H, Gama de Abreu M, Schultz MJ, Pelosi P; LAS VEGAS investigators; PROVE Network; Clinical Trial Network of the European Society of Anaesthesiology. Intraoperative ventilation settings and their associations with postoperative pulmonary complications in obese patients. Br J Anaesth. 2018 Oct;121(4):899-908. doi: 10.1016/j.bja.2018.04.021. Epub 2018 Jun 2.
• Duggan M, Kavanagh BP. Pulmonary atelectasis: a pathogenic perioperative entity. Anesthesiology. 2005 Apr;102(4):838-54. doi: 10.1097/00000542-200504000-00021.
• Hedenstierna G, Edmark L. Mechanisms of atelectasis in the perioperative period. Best Pract Res Clin Anaesthesiol. 2010 Jun;24(2):157-69. doi: 10.1016/j.bpa.2009.12.002.

Study record dates

Study Major Dates

• Study Start (Actual): September 15, 2024
• Primary Completion (Actual): June 26, 2025
• Study Completion (Actual): August 5, 2025

Study Registration Dates

• First Submitted: November 27, 2025
• First Submitted That Met QC Criteria: February 9, 2026
• First Posted (Actual): February 17, 2026

Study Record Updates

• Last Update Posted (Actual): May 19, 2026
• Last Update Submitted That Met QC Criteria: May 17, 2026
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Keywords: oxygenation; mechanical power; Lung ultrasonography; lung ultrasound score; Flow-Controlled Ventilation (FCV); Volume-Controlled Ventilation (VCV); Pressure-Controlled Ventilation (PCV); Perioperative atelectasis
• Additional Relevant MeSH Terms: Respiratory Tract Diseases; Lung Diseases; Pulmonary Atelectasis
• Other Study ID Numbers: Ivstrh 2024/241

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: We do not plan to share IPD for data security reasons.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No