Effects of Ultrasound-guided Recruitment Manoeuvres on Postoperative Pulmonary Complications in OSA Patients Undergoing Total Laparoscopic Hysterectomy
Phase: NA
Conditions: Total Laparoscopic Hysterectomy, Atelectasis, Postoperative
Sponsor: The First Affiliated Hospital of Xinxiang Medical College

Research Proposal 
 
 
 
 
Effects of ultrasound-guided recruitment manoeuvres 
on postoperative pulmonary complications in OSA 
patients undergoing total laparoscopic hysterectomy: 
a randomized controlled trial 
 
 
 
 
 
Applicant: The First Affiliated Hospital of Henan Medical University 
Principal Investigator: Zheng Kaiyuan 
Date: 15 April 2025 
 
 

Introduction 
Atelectasis occurs during general anesthesia in up to 90% of patients1. Atelectasis can 
occur during anesthesia induction and persist for up to two days postoperatively2. 
Clinical evidence has established its role in precipitating postoperative pulmonary 
complications (PPCs), with commonly observed manifestations ranging from 
pneumonia and pleural effusion to more severe conditions like pneumothorax and 
ARDS3. The use of anesthetic agents, pneumoperitoneum, changes in body 
positioning, and other factors can contribute to and exacerbate the development of 
atelectasis4-8. Due to factors such as increased BMI and reduced alveolar surfactant 
production in obese patients, atelectasis is more likely to occur during surgery9. In 
addition, a proportion of patients undergoing total laparoscopic hysterectomy are 
obese and have concomitant obstructive sleep apnea (OSA). The occurrence of sleep 
apnea in OSA patients postoperatively is a major cause of PPCs 10. The administration 
of opioids during the perioperative period is associated with an increased incidence of 
apnoea.11, further exacerbating the onset and progression of PPCs12. 
Lung-protective ventilation strategies have been developed to mitigate ventilator-
associated lung injury and protect pulmonary tissue13. These strategies mainly include 
low tidal volume ventilation, individualized PEEP, recruitment maneuvers (RMs), and 
low plateau pressure. Currently, sustained inflation and incremental PEEP methods 
are commonly used for RMs. However, the optimal lung recruitment pressure during 
RM remains controversial, and blind recruitment may result in inadequate recruitment 
or excessive alveolar distention14. Additionally, excessive airway pressure during RM 
can elevate intrathoracic pressure, reduce venous return, and lead to significant 
fluctuations in the patient's hemodynamics15. 
Computed tomography (CT) is widely regarded as the gold standard for evaluating the 
effectiveness of RMs. However, due to its radiation risks, high cost, and limited 
intraoperative feasibility, it is not routinely used for evaluating RM during surgery. In 
previous studies, researchers have proposed using methods such as X-ray and 

Electrical Impedance Tomography (EIT) to assess the effectiveness of RM16 17. 
However, there is still a lack of authoritative guidelines for evaluating RM. 
As a diagnostic tool, ultrasound offers the advantages of being portable, non-invasive, 
free of ionising radiation, and capable of producing real-time images. It has been 
widely employed in operating rooms, intensive care units, and emergency 
departments. Studies have demonstrated that pulmonary ultrasound is a rapid and 
reliable method for identifying perioperative atelectasis, with a sensitivity exceeding 
85%, and both specificity and accuracy rates exceeding 90%18. Ultrasound-guided 
RM can adjust parameters such as lung recruitment pressure, duration, and others 
based on individual patient characteristics, ensuring timely adaptation to meet the 
specific needs of each patient19.  
End-Expiratory Lung Volume (EELV) is defined as the volume of gas retained in the 
lungs at the end of expiration during mechanical ventilation, which is an important 
indicator reflecting the effectiveness of lung recruitment. By calculating the difference 
of EELV under various conditions, the change of lung volume after recruitment can be 
quantitatively evaluated, the alveolar volume after recruitment can be estimated, and 
the effectiveness of RM can be evaluated20. 
Therefore, we aim to evaluate the lung-protective effects of ultrasound-guided lung 
recruitment maneuvers in patients with OSA undergoing total laparoscopic 
hysterectomy and to explore the efficacy of EELV measurement in assessing the 
effectiveness of these maneuvers. 
 
 

Method and analysis  
Trial status 
This study has been reviewed and approved by the ethics committee of the First 
Affiliated Hospital of Henan Medical University. Participant recruitment is scheduled 
to commence in May 2025, with an anticipated completion date of August 2026. 
Study design and setting 
We conducted a single-center, randomized controlled trial aimed at determining 
whether ultrasound-guided lung recruitment provides better recruitment outcomes and 
reduces the incidence of PPCs. Additionally, the study will explore the effectiveness 
of EELV measurement in evaluating RMs. This study will be carried out at the First 
Affiliated Hospital of Henan Medical University. 
Eligibility criteria 
Inclusion criteria 
⚫ 
Age ≥ 18 years; 
⚫ 
Scheduled for elective total laparoscopic hysterectomy; 
⚫ 
American Society of Anesthesiologists (ASA) I to III; 
⚫ 
BMI > 28 kg/m²; 
⚫ 
STOP-BANG score ≥ 3. 
Exclusion criteria  
⚫ 
Abnormal findings on preoperative chest X-ray or CT, such as atelectasis, 
pneumothorax, thoracic deformity, pleural effusion, or neuromuscular diseases; 
⚫ 
Pre-existing severe pulmonary diseases; 
⚫ 
Severe cardiac arrhythmias or a history of cardiac surgery; 
⚫ 
Allergy to any medications used in the study. 
Withdrawal Criteria: 

⚫ 
Severe subcutaneous emphysema interfering with lung ultrasound examination; 
⚫ 
Postoperative transfer to the ICU with tracheal intubation in place; 
⚫ 
Conversion from laparoscopic to open surgery during the procedure; 
⚫ 
Perioperative hemodynamic instability. 
Randomization and blinding 
This study will adopt a randomized, single-blind controlled trial design. According to 
CONSORT guidelines, we will allocate patients randomly to one of three groups 
based on a computer-generated randomization list: the SRM group (sustained inflation 
recruitment maneuver, n=30), the PRM group (incremental PEEP recruitment 
maneuver, n=30), and the LRM group (lung ultrasound-guided recruitment maneuver, 
n=30). Patients will remain blinded to their group assignments throughout the study. 
 
 
Fig. 1. CONSORT flow diagram 
the SRM group (Sustained inflation recruitment maneuvers, n = 30);             
the PRM group (Incremental PEEP recruitment maneuvers, n = 30);               
the LRM group (Lung Ultrasound-guided recruitment maneuvers, n = 30)

Methods of the Trial 
Anesthesia Protocol 
Patients will not receive preoperative medication. Hemodynamic monitoring, 
including continuous electrocardiogram, non-invasive blood pressure, and pulse 
oximetry, is continuously monitored. After oxygenation with 100% oxygen via a face 
mask for 3 minutes, anesthesia induction will be performed with intravenous 
administration of midazolam (0.04–0.05 mg/kg), sufentanil (0.4–0.6 μg/kg), 
rocuronium (0.6 mg/kg), and etomidate (0.15–0.3 mg/kg). An appropriately sized 
reinforced endotracheal tube will be selected for intubation based on the patient’s 
height. 
During the maintenance of general anesthesia, 2% sevoflurane will be administered as 
the inhalation anesthetic, along with a continuous infusion of propofol (0.8–1.8 
mg/kg/h) and remifentanil (0.1–0.3 μg/kg/h) using a micro-infusion pump. 
Rocuronium will be administered intermittently to maintain anesthesia. Intraoperative 
anesthetic dosing adjustments will be based on blood pressure, heart rate, and depth of 
anesthesia.  
After tracheal intubation, the Dräger Primus anesthesia machine (Dräger, Germany) 
will be used in volume-controlled ventilation mode, with a tidal volume of 6-8 ml/kg 
of ideal body weight, FiO2 set to 0.5, I: E ratio set to 1:2, a respiratory rate of 12-18 
breaths/min, and end-tidal carbon dioxide (PETCO2) maintained at 35-45 mmHg. 
Radial artery puncture and catheterization for pressure monitoring will be performed    
at T1 (immediately after tracheal intubation), and 1 mL of arterial blood will be  
collected for blood gas analysis. An additional 1 mL of arterial blood will be collected 
for blood gas analysis at T5 (30 minutes after extubation ). 
 
 

 
Fig. 2. Schematic diagram of the study protocol. 
T0: before anesthesia induction; T1: immediately after tracheal intubation; T2: after 
the first lung recruitment; T3: immediately after the surgery; T4: after the second lung 
recruitment; T5: 30 minutes after extubation; SRMs: sustained inflation recruitment 
maneuver; PRMs: incremental PEEP recruitment maneuvers; LRMs: lung ultrasound-
guided recruitment maneuvers; LUS: lung ultrasound; TLH: total laparoscopic 
hysterectomy. 
Postoperative Follow-Up 
Postoperative follow-up will monitor the occurrence of pulmonary complications, 
including pneumonia, atelectasis, and incision infections, within three days. The 
ARISCAT score, the Clinical Pulmonary Infection score, and the Quality of 
Recovery-15 scale will also be recorded. 
Lung Recruitment Methods 
The SRM group (Sustained inflation recruitment maneuver): The APL valve on the 
anesthesia machine will be adjusted to 30 cmH₂O, and the rapid oxygen inflow valve 
will be pressed to increase the pressure to the maximum, maintaining the pressure for 
30 seconds. 
The PRM group (Incremental PEEP recruitment maneuver): Starting from 5 cmH₂O, 
PEEP will be titrated upwards in 5 cmH₂O increments every 30 seconds until a 

maximum of 30 cmH₂O is reached. After maintaining for 40 seconds, PEEP will be 
decreased by 5 cmH₂O every 30 seconds until it returns to the pre-recruitment level. 
The LRM group (Lung ultrasound-guided recruitment maneuver): Lung ultrasound 
will be performed on patients. If any lung region has an LUS score ≥ 2, ultrasound-
guided RM will be performed; otherwise, no operation will be conducted. After the 
ultrasound examination, the probe will be positioned over the lung region exhibiting 
the most severe aeration loss (highest LUS) to guide the RMs. The ventilator will be 
set to pressure-controlled ventilation (PCV), maintaining the inspiratory pressure at 40 
cmH₂O. PEEP will be gradually increased from 5 cmH₂O, with increments of 5 
cmH₂O every 5-10 seconds, until ultrasound shows no atelectatic areas. The pressure 
will be maintained at 40 cmH₂O for 40 seconds. An airway pressure ceiling of 40 
cmH₂O will be established, and the pressure and the time used for the RM will be 
recorded. 
Measurement of Recruitment Volume 
After performing the RMs in the PRM group and LRM group, the respiratory rate will 
be adjusted to 6 breaths per minute. Record the PEEP (PEEP1) used during RM. The 
exhaled tidal volume (VT1) will be recorded. Then, PEEP will be adjusted to 5 cmH₂O 
(PEEP2), and the expiratory tidal volume (VT2) will be recorded. The difference 
between VT1 and VT2 will be calculated as ΔEELV. Baseline tidal volume and airway 
pressure will be recorded immediately before the RMs. The recruitment volume will 
be calculated using the following formula20 21.  
Recruitment volume = (VT2- VT1) – [VT1 / (Plat – PEEP2)] × (PEEP1 - PEEP2) 
Lung Ultrasound Examination 
Lung ultrasound will be performed on the patient by using a convex probe at the 
following time points: before anesthesia induction (T0), immediately after tracheal 
intubation (T1), after the first lung recruitment (T2), immediately after the surgery 
(T3), after the second lung recruitment (T4), and 30 minutes after extubation (T5). 

Each lung will be divided into six regions (L1-L6, R1-R6) based on three vertical 
lines (the parasternal line, the anterior axillary line, and the posterior axillary line) and 
two horizontal lines (the nipple line and the diaphragm line). Each region will be 
scored by using the LUS Score proposed by Monastesse et al.22, which has 
demonstrated sufficient sensitivity for detecting the occurrence of atelectasis during 
laparoscopic surgery. Lung ultrasound examination will be performed by two 
anesthesiologists independently, and the final score will be the average of the scores 
given by both anesthesiologists. 
Outcome Assessment 
The primary outcome is the lung ultrasound score (LUS), which will be measured at 
time points T1 through T5. 
Secondary outcomes include the recruitment volume, as measured by the ΔEELV 
method. 
Data collection 
Data collection will adhere to standardized operating procedures to ensure accuracy 
and reliability. We will collect preoperative information, including age, ASA 
classification, height, weight, STOP-BANG score, and calculate BMI and ideal body 
weight. We will also record intraoperative information, including intraoperative fluid 
volume, blood loss, surgery duration, pneumoperitoneum duration, 
pneumoperitoneum pressure, anesthesia duration, mechanical ventilation time, PACU 
stay time, and pre- and post-recruitment blood pressure, heart rate, peak airway 
pressure, plateau airway pressure, arterial oxygen partial pressure, arterial carbon 
dioxide partial pressure, hospital length of stay, the ARISCAT score, the Clinical 
Pulmonary Infection score (CPIS), and the quality of recovery-15 scale (qor-15). 
Additionally, we will calculate the oxygenation index, dynamic lung compliance, 
alveolar-arterial oxygen pressure gradient, respiratory index, and dead space 
ventilation. 

Statistical Analysis 
Statistical analysis will be performed with the SPSS 26.0 software. Data for normally 
distributed continuous variables are presented as the mean ± standard deviation (x̅  ± 
s). For non-normal data, express it as the median (M) and interquartile range (IQR). 
The paired sample t-test will be used to compare the repeated measurements of the 
normal distribution at different time points. Continuous variables that are not 
normally distributed will be compared using the rank-sum test. Categorical data will 
be expressed as frequencies and compared by the Chi-square test. Statistical 
significance will be defined as a p-value < 0.05. 
Sample size estimation 
The calculation of the sample size is based on the primary outcome. Based on the 
previous studies23, at the end of the surgery, the LUS score of patients undergoing 
ultrasound-guided recruitment maneuver was 7.67±1.15, while that of patients using 
sustained inflation was 9.70±1.02. We assume that the recruitment effects of the 
incremental PEEP method and sustained inflation method are the same.  Assuming a 
significance level of α = 0.05, a power of β = 0.1, a dropout rate of 20%, a total of 90 
participants were required, as calculated using PASS 15.0 software. 
Ethics and dissemination  
This study protocol was approved by the Ethics Committee of the First Affiliated 
Hospital of Henan Medical University on April 22, 2025 ( EC-025-117). Written 
informed consent will be obtained from all participants. The results of this study will 
be disseminated through publication in internationally peer-reviewed scientific 
journals. 
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