Evaluation of the Effects of Intraoperative Ventilation Modes on Perioperative Atelectasis in Patients Undergoing Hysterectomy by Lung Ultrasonography
Conditions: Atelectasis, Postoperative Pulmonary
Sponsor: Sehit Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital

STUDY PROTOCOL 
Official Title: 
Evaluation of the Effects of Intraoperative Ventilation Modes on Perioperative Atelectasis in 
Patients Undergoing Hysterectomy by Lung Ultrasonography 
NCT Number: 
NCT07413575 
Organization’s Unique Protocol ID: 
Ivstrh 2024/241 
Protocol Version: 
Version 1.0 
Protocol Date: 
05 August 2025 
Sponsor: 
Sehit Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital 
Study Location: 
Istanbul 
 
 
 

 
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1. Background and Rationale 
Postoperative pulmonary complications, including atelectasis, pneumonia, pulmonary 
embolism, pleural effusion, pulmonary edema, and pneumothorax, are associated with 
prolonged hospitalization and increased morbidity and mortality. 
Atelectasis occurs in approximately 80–100% of patients receiving general anesthesia. 
Mechanical ventilation, while essential, may contribute to ventilator-induced lung injury 
(VILI) through atelectotrauma, barotrauma, volutrauma, and biotrauma. 
Mechanical power represents the total energy transferred from the ventilator to lung tissue and 
is influenced by tidal volume (Vt), airway pressures, respiratory rate (RR), inspiratory flow, 
and positive end-expiratory pressure (PEEP). 
Hysterectomy procedures present a particularly high risk for perioperative atelectasis due to 
the abdominal surgical approach, prolonged operative duration, Trendelenburg positioning, 
and pneumoperitoneum-related diaphragmatic displacement. 
Lung ultrasonography is a sensitive bedside modality for detecting anesthesia-related 
atelectasis and allows dynamic perioperative monitoring without radiation exposure. 
Flow-controlled ventilation (FCV) is a ventilation mode delivering constant inspiratory and 
expiratory flow, enabling precise assessment of dynamic lung compliance and individualized 
ventilatory settings. Comparative clinical data between FCV and conventional ventilation 
modes remain limited. 
2. Study Objectives 
Primary Objective 
To determine whether intraoperative ventilation mode affects the development of 
perioperative atelectasis measured quantitatively by lung ultrasonography. 
Secondary Objectives 
To compare ventilation modes with respect to: 
 
Mechanical power of ventilation 
 
Oxygenation parameters 
3. Study Design 
This study is observational in nature; the choice of ventilation mode was determined solely by 
the attending anesthesiologist as part of routine clinical care, and no study-driven intervention 
was applied. 
 
Study Type: Observational 
 
Design: Prospective cohort 
 
Time Perspective: Prospective 
 
Number of Groups: 3 

 
2 
 
Enrollment: 78 patients 
 
Sampling Method: Non-probability sampling 
 
Study Period: September 15, 2024 – August 05, 2025 
 
Setting: Single center 
Patients were grouped according to the ventilation mode selected by the attending 
anesthesiologist as part of routine clinical care. No intervention was assigned by the study 
protocol. 
4. Study Population 
Inclusion Criteria 
 
Female patients ≥45 years of age 
 
Scheduled for elective hysterectomy 
 
Expected surgery duration >2 hours 
 
American Society of Anesthesiologists (ASA) Physical Status I–III 
 
Planned total intravenous anesthesia 
Exclusion Criteria 
 
ASA Physical Status ≥IV 
 
Body mass index (BMI) >35 kg/m² 
 
Planned postoperative intensive care admission 
 
Neuromuscular disease 
 
Uncontrolled asthma 
 
Chronic obstructive pulmonary disease (GOLD stage IV) 
 
Chest wall deformity or scoliosis 
 
Prior pulmonary resection 
 
History of spontaneous pneumothorax 
 
Preference for inhalational anesthesia 
 
Inability to provide informed consent 
5. Study Groups 
Flow-Controlled Ventilation (FCV) 
Constant inspiratory and expiratory flow with linear pressure changes and inspiratory-to-
expiratory ratio of 1:1. 
Pressure-Controlled Ventilation (PCV) 
Peak airway pressure predetermined; inspiratory time and respiratory rate fixed. 
Volume-Controlled Ventilation (VCV) 
Fixed tidal volume delivered with constant flow; airway pressure varies. 
 
 
 

 
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6. Study Procedures 
Recorded Parameters 
Hemodynamic and Monitoring Data 
 
Heart rate (HR) 
 
Mean arterial pressure (MAP) 
 
Peripheral oxygen saturation (SpO₂) 
 
BIS monitoring (depth of anesthesia) 
Respiratory and Ventilator Parameters 
 
Peak airway pressure (Ppeak) 
 
Plateau pressure 
 
Positive end-expiratory pressure (PEEP) 
 
Tidal volume (Vt) 
 
Respiratory rate (RR) 
 
End-tidal carbon dioxide (EtCO₂) 
 
Fraction of inspired oxygen (FiO₂) 
 
Flow rate 
Calculated Respiratory Mechanical Parameters 
  Mechanical power (J/min) 
  Lung compliance (mL/cmH₂O) 
Arterial Blood Gas Parameters 
 
Partial pressure of arterial oxygen (PaO₂, mmHg) 
 
PaO₂/FiO₂ ratio (mmHg) 
 
Partial pressure of carbon dioxide (PaCO₂, mmHg) 
 
Lung Ultrasonography Assessment 
 
Lung Ultrasound Score (LUS) 
Postoperative Clinical Assessment 
 
Pain intensity assessed using the Visual Analog Scale (VAS) 
Measurement Time Points 
Lung Ultrasonography (LUS) Measurements 
 
Preoperatively (baseline value) 
 
At transfer from the PACU to the ward 

 
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 
Postoperative 2nd hour 
 
Postoperative 24th hour 
Changes from preoperative baseline values were used to evaluate perioperative atelectasis. 
Pain Assessment (VAS Scores) 
 
Postoperative 2nd hour 
 
Postoperative 6th hour 
 
Postoperative 12th hour 
 
Postoperative 24th hour 
Timing of Intraoperative and Perioperative Parameter Measurements 
 
Preoperative period 
 
After anesthesia induction 
 
Before and after pneumoperitoneum 
 
Before and after surgical positioning 
 
At 30-minute intervals during the intraoperative period 
 
During the Post-Anesthesia Care Unit (PACU) period 
7-Outcome Measures 
PRİMARY OUTCOME MEASURES 
 Perioperative atelectasis 
Description: 
Perioperative atelectasis will be quantified using Lung Ultrasound Score obtained via 
standardized bedside lung ultrasonography. Each lung region will be graded using a validated 
aeration scoring system (0 = normal aeration to 3 = consolidation). Total score range: 0–36 
points. 
Outcome Metric: 
Difference between postoperative and preoperative total LUS (ΔLUS, points). 
Measurement Time Points: 
 
Preoperative baseline 
 
At discharge from Post-Anesthesia Care Unit (PACU) 
 
Postoperative 2 hours 
 
Postoperative 24 hours 
Time Frame: 24 Hours 
 
 

 
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SECONDARY OUTCOME MEASURES 
Evaluation of Oxygenation and Mechanical Power 
Description:  
Mechanical power and oxygenation were evaluated across three different ventilation modes 
based on the ventilation parameters set by the anesthesiologist. Mechanical power was 
assessed at predefined time intervals throughout mechanical ventilation. Oxygenation was 
evaluated preoperatively and in the post-anesthesia care unit (Post-Anesthesia Care Unit, 
PACU) using the partial pressure of oxygen (pO₂) and the ratio of arterial partial pressure of 
oxygen to fraction of inspired oxygen (PaO₂/FiO₂ ratio).  
Unit of Measure: Joules per minute (J/min), representing the mechanical power applied to the 
respiratory system. 
Oxygenation will be assessed using arterial blood gas analysis measuring: • PaO₂ (mmHg) • 
PaO₂/FiO₂ ratio (mmHg) 
Time Frame: Perioperative period 
8. Statistical Analysis Plan 
8.1 General Principles 
All statistical analyses will be conducted using NCSS (Number Cruncher Statistical 
System) 2020 Statistical Software (NCSS LLC). 
Statistical significance will be assessed using two-sided tests, with a significance level of p < 
0.05. Results will be reported with 95% confidence intervals (CI). 
8.2 Sample Size Determination 
Sample size was calculated using G*Power (v3.1.9.7) (Heinrich Heine University 
Düsseldorf). 
Assuming: 
 
Type I error (α): 0.05 
 
Statistical power: 80% 
 
Three-group comparison design 
The minimum required sample size was 22 patients per group (total n = 66). 
To account for potential data loss, protocol deviations, or dropouts, the study planned to 
enroll 78 participants. 
8.3 Data Presentation 
 
Continuous variables will be summarized as: 
o Mean ± standard deviation (SD) 
o Median 
o Minimum–maximum values 

 
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 
Categorical variables will be expressed as: 
o Frequency (n) 
o Percentage (%) 
8.4 Assessment of Normality 
Distribution of continuous variables will be evaluated using: 
 
Shapiro–Wilk test 
 
Skewness and kurtosis values 
 
Visual inspection of box plot graphs 
8.5 Between-Group Comparisons 
For comparisons among the three ventilation groups: 
Normally distributed variables 
 
One-Way Analysis of Variance (One-Way ANOVA) 
 
Bonferroni post hoc test to identify pairwise differences 
Non-normally distributed variables 
 
Kruskal–Wallis test 
 
Dunn test for multiple comparisons 
8.6 Within-Group (Repeated Measures) Analysis 
To evaluate intraoperative and perioperative changes over time: 
Normally distributed repeated measurements 
 
Repeated Measures ANOVA 
Non-normally distributed repeated measurements 
 
Friedman test 
8.7 Analysis of Categorical Variables 
Categorical outcomes (e.g., incidence of postoperative findings) will be analyzed using: 
 
Pearson’s Chi-Square test 
8.8 Analysis Population 
All enrolled patients with available outcome data will be included in the analysis. 
Missing data will not be imputed; analyses will be performed using available-case data. 
 

 
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8.9 Software and Reporting Standards 
All analyses will follow accepted biostatistical standards for observational clinical studies. 
Results will be reported in accordance with CONSORT-style recommendations where 
applicable. 
9. Ethical Considerations 
The study was reviewed and approved by the Clinical Research Ethics Committee of Sehit 
Prof. Dr. Ilhan Varank Sancaktepe Training and Research Hospital, affiliated with the 
University of Health Sciences (Approval No: 2024/241). 
Written informed consent was obtained from all participants. 
The study adhered to: 
 
Declaration of Helsinki 
 
Good Clinical Practice principles 
10. Data Management and Confidentiality 
 
No biospecimens retained. 
 
Data anonymized prior to analysis. 
 
Only study investigators had access to coded datasets. 
11. Safety Considerations 
As an observational study, all interventions were part of routine anesthesia care. 
No additional risk beyond standard clinical management was introduced. 
No study-specific adverse event monitoring was required because all procedures were part of 
standard clinical practice. 
12. Study Completion 
 
Primary Completion Date: June 26, 2025 
 
Study Completion Date: August 05, 2025 
 
Recruitment Status: Completed 
 
 
 
 
 
 

 
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INFORMED CONSENT FORM (ICF) 
FOR THE RESEARCH STUDY ENTITLED: 
“Evaluation of the Effects of Intraoperative Ventilation Modes on Perioperative 
Atelectasis in Patients Undergoing Hysterectomy by Lung Ultrasonography” 
 
PLEASE READ CAREFULLY! 
You are being invited to participate in this study. 
Before agreeing to take part, you should understand the purpose of the study and make your 
decision freely after being informed. 
Please read this information prepared specifically for you with care. 
Feel free to ask any questions and request clear answers. 
 
WHAT IS THE PURPOSE OF THE STUDY? 
In hysterectomy operations, factors such as abdominal surgery, prolonged duration of the 
procedure, and the head-down position during surgery may cause a lobe or a certain part of 
the lungs to collapse and not fill with air after the operation. This condition is defined as 
atelectasis. 
In this study, we aim to evaluate the effects of ventilation modes—routinely used in the 
operating room and not proven to be superior to one another—that help maintain breathing 
during surgery, on the development of postoperative atelectasis using lung ultrasonography. 
 
WHAT ARE THE CONDITIONS FOR PARTICIPATION? 
To participate in this study, you must: 
 
Be 45 years of age or older, 
 
Be scheduled to undergo a hysterectomy expected to last longer than 2 hours, 
 
Be in the patient category for whom total intravenous anesthesia (anesthesia 
administered entirely through intravenous medications) is preferred by the 
responsible anesthesiologist. 
 
WHAT WILL BE DONE AND HOW WILL IT BE PERFORMED? 
During this research, no intervention or treatment other than the treatment planned by your 
responsible physicians will be applied to you or your relatives. 
Only the data recorded during routine procedures will be analyzed after the data collection 
phase of the study is completed. 

 
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HOW MANY PARTICIPANTS WILL BE INCLUDED? 
Approximately 78 patients will be included in this study. 
 
HOW LONG WILL THE STUDY LAST? 
The study is expected to last approximately 1 year. 
 
WHAT ARE THE POSSIBLE BENEFITS OF PARTICIPATING? 
The aim of the study is to evaluate the effects of ventilation modes routinely used in the 
operating room on the development of postoperative atelectasis. 
Although there may be no direct benefit to you, the results may contribute to improving 
medical practice in the future. 
 
WHAT ARE THE POSSIBLE RISKS OF PARTICIPATING? 
This is an observational study. 
No additional treatment will be applied other than the procedures required for your medical 
care. Therefore, participation does not pose any additional risk beyond the standard risks 
associated with anesthesia and surgery. 
 
WHO SHOULD I CONTACT IF I EXPERIENCE ANY PROBLEMS 
DURING THE STUDY? 
Dr. Tuğçe Türkan Tanman 
Department of Anesthesiology and Reanimation 
Phone: +90 216 603 33 00 (Extension: 1751) 
 
WILL ANY COSTS BE COVERED WITHIN THE STUDY? 
All treatments applied during the study are part of your routine care, and no additional 
expenses will arise. 
 
WILL I RECEIVE ANY PAYMENT FOR PARTICIPATING? 

 
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Participants will not receive any payment. 
 
WHAT SHOULD I DO IF I DO NOT WANT TO PARTICIPATE OR WISH 
TO WITHDRAW? 
Participation in this study is entirely voluntary. 
You may refuse to participate or withdraw from the study at any time. 
The results of the research will be used for scientific purposes. 
If you withdraw or are removed from the study, your data will not be used for scientific 
purposes. 
 
WILL MY INFORMATION BE KEPT CONFIDENTIAL? 
All your medical and personal information will be kept confidential. Even if the research is 
published, your identity will not be disclosed. 
However, study monitors, auditors, ethics committees, and official authorities may access 
your medical records when necessary. These records will remain confidential. By signing this 
informed consent form, you authorize such access. 
Your information will not be disclosed to the public. Even if study results are published, your 
identity will remain confidential. If new information that may affect you becomes available, 
you will be informed in a timely manner. 
 
CONSENT TO PARTICIPATE 
I have read the above information, which must be provided to volunteers before participation, 
and have also listened to the verbal explanation given by the physician named below. 
I have asked all questions that came to mind and fully understood the written and verbal 
explanations provided to me. 
I was given sufficient time to decide whether or not to participate. 
I voluntarily agree to participate in this research without any pressure or coercion. 
Under these conditions, I authorize the study investigator to review, transfer, and process my 
medical information and accept the invitation to participate in this research entirely of my 
own free will. 
By signing this form, I understand that I do not waive any rights granted to me by local laws. 
A signed and dated copy of this form has been given to me. 

 
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PARTICIPANT 
Name and Surname: ___________________________ 
Signature: __________________________________ 
Address: ___________________________________ 
Phone: _____________________________________ 
Date: ______________________________________ 
 
INVESTIGATOR 
Name and Surname: ___________________________ 
Signature: __________________________________ 
Date: ______________________________________ 
 
WITNESS (WHEN REQUIRED) 
Name and Surname: ___________________________ 
Role: _______________________________________ 
Signature: __________________________________ 
Date: ______________________________________