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Comparison of BMI-adjusted positive end-expiratory pressure versus zero positive end-expiratory pressure on optic nerve sheath diameter measured by ultrasonography in adults undergoing elective laparoscopic cholecystectomy

Protocol summary

Study aim
To evaluate the effect of positive end expiratory pressure on ultrasonographic optic nerve sheath diameter, as a surrogate marker of intracranial pressure, in adults undergoing elective laparoscopic cholecystectomy under general anesthesia.
Design
Single center, parallel group, randomized controlled, double blind clinical trial with 50 participants allocated equally by computer generated block randomization using sealed envelopes.
Settings and conduct
The trial will be conducted at a tertiary hospital called "Iraqi hospital" in Kufa. Participants will undergo standard general anesthesia and laparoscopic cholecystectomy. Participants, outcome assessor, and data analyst will remain blinded. Group allocation will be concealed using sequentially numbered opaque sealed envelopes.
Participants/Inclusion and exclusion criteria
Inclusion criteria: Adults aged 18 to 70 years, with American Society of Anesthesiologists physical status I to III, undergoing elective laparoscopic cholecystectomy. Exclusion criteria: ophthalmic disease, cerebrovascular disease, significant respiratory disease, pregnancy, inability to undergo optic nerve sheath ultrasonography, refusal to participate.
Intervention groups
Control group receives volume controlled ventilation with zero positive end expiratory pressure. Intervention group receives body mass index adjusted positive end expiratory pressure of 5, 8, or 10 centimeters of water.
Main outcome variables
Primary outcome is optic nerve sheath diameter measured by ultrasonography. Secondary outcomes are mean arterial pressure, heart rate, peak inspiratory pressure, plateau pressure, driving pressure, and their association with optic nerve sheath diameter.

General information

Reason for update
Acronym
IRCT registration information
IRCT registration number: IRCT20260627069955N1
Registration date: 2026-08-01, 1405/05/10
Registration timing: prospective

Last update: 2026-08-01, 1405/05/10
Update count: 0
Registration date
2026-08-01, 1405/05/10
Registrant information
Name
Muslim Ghali Yousef Al-Tamimi
Name of organization / entity
Country
Iran (Islamic Republic of)
Phone
+98 21 2284 4920
Email address
muslimghaly@gmail.com
Recruitment status
recruiting
Funding source
Expected recruitment start date
2026-09-03, 1405/06/12
Expected recruitment end date
2026-12-03, 1405/09/12
Actual recruitment start date
empty
Actual recruitment end date
empty
Trial completion date
empty
Scientific title
Comparison of BMI-adjusted positive end-expiratory pressure versus zero positive end-expiratory pressure on optic nerve sheath diameter measured by ultrasonography in adults undergoing elective laparoscopic cholecystectomy
Public title
The effect of positive end-expiratory pressure (PEEP) on optic nerve sheath diameter during laparoscopic cholecystectomy
Purpose
Treatment
Inclusion/Exclusion criteria
Inclusion criteria:
Adults aged 18–65 years. ASA physical status I–III. Scheduled for elective laparoscopic cholecystectomy under general anesthesia. Ability to provide written informed consent. Eligible for volume-controlled mechanical ventilation during surgery.
Exclusion criteria:
History of acute or chronic ophthalmic disease (e.g., glaucoma, optic neuritis, retinal disease, previous ocular surgery affecting ONSD measurement). Known cerebrovascular or neurological disease associated with altered intracranial pressure (such as stroke, intracranial tumor, hydrocephalus, traumatic brain injury). Significant respiratory disease (such as COPD, severe asthma, restrictive lung disease) that may influence ventilatory management. Contraindications to laparoscopic surgery or pneumoperitoneum. Inability to obtain adequate ultrasonographic visualization of the optic nerve sheath. Pregnancy.
Age
From 18 years old to 65 years old
Gender
Both
Phase
N/A
Groups that have been masked
  • Participant
  • Outcome assessor
  • Data analyser
Sample size
Target sample size: 50
Randomization (investigator's opinion)
Randomized
Randomization description
Patients will be randomized in a 1:1 ratio into either the control group (0 cmH₂O PEEP) or the PEEP group using block randomization with a fixed block size of four. The unit of randomization will be the individual patient. No stratification will be applied. The randomization sequence will be generated by an independent investigator using a computer-based random number generator (IBM SPSS Statistics version 26). The sequence will be created before patient enrollment and will consist of randomly permuted blocks to ensure balanced allocation between the two groups throughout the recruitment period. Allocation concealment will be maintained using sequentially numbered, opaque, sealed envelopes prepared by a researcher not involved in patient recruitment, anesthesia management, outcome assessment, or statistical analysis. Immediately before induction of anesthesia, the attending anesthesiologist will open the next envelope in sequence to determine group assignment. Thus, allocation concealment will be carried out until the moment of assignment.
Blinding (investigator's opinion)
Double blinded
Blinding description
Participants will be blinded to group allocation and will not be informed whether they receive zero PEEP or BMI-adjusted PEEP during mechanical ventilation. The attending anesthesiologist responsible for intraoperative ventilator management cannot be blinded because adjustment of PEEP is required according to the assigned intervention. However, this anesthesiologist will have no role in outcome assessment, data collection, or statistical analysis. The ultrasonographer who performs all optic nerve sheath diameter (ONSD) measurements, the investigators responsible for collecting perioperative data, and the data analyst will remain blinded to treatment allocation throughout the study. Group allocation will be concealed using sequentially numbered, opaque, sealed envelopes prepared by an independent researcher. The envelopes will be opened only after patient enrollment and immediately before the induction of anesthesia. Study data will be be coded before statistical analysis so that the data analyst remains unaware of group assignments until completion of the final analysis. No Data and Safety Monitoring Board (DSMB) is planned because of the small sample size and the low-risk nature of the study. Manuscript preparation will be based on coded data after completion of the analysis.
Placebo
Not used
Assignment
Parallel
Other design features

Secondary Ids

empty

Ethics committees

1

Ethics committee
Name of ethics committee
Research Ethics Committee of the School of Medicine, Shahid Beheshti University of Medical Sciences
Street address
Third floor, School of Medicine, next to Taleghani Hospital, Evin, Shahid Chamran Highway
City
Tehran
Province
Tehran
Postal code
19839-63113
Approval date
2026-06-02, 1405/03/12
Ethics committee reference number
IR.SBMU.MSP.REC.1405.162

Health conditions studied

1

Description of health condition studied
Symptomatic cholelithiasis requiring elective laparoscopic cholecystectomy
ICD-10 code
Z90.4
ICD-10 code description
Acquired absence of other specified parts of digestive tract

Primary outcomes

1

Description
Optic nerve sheath diameter measured by ultrasonography
Timepoint
Before induction of anesthesia, immediately after tracheal intubation, 5 minutes after pneumoperitoneum, 5 minutes after positive end expiratory pressure application, 5 minutes after peritoneal deflation, and 5 minutes after tracheal extubation.
Method of measurement
Measurement of optic nerve sheath diameter by orbital ultrasonography using a seven point five megahertz linear ultrasound probe, with measurements obtained from both eyes at three millimeters behind the optic disc.

Secondary outcomes

empty

Intervention groups

1

Description
Intervention group: Patients will receive volume controlled mechanical ventilation with positive end expiratory pressure applied 5 minutes after pneumoperitoneum according to body mass index. Patients with body mass index less than 25 kilograms per square meter will receive 5 centimeters of water positive end expiratory pressure, those with body mass index 25 to 30 kilograms per square meter will receive 8 centimeters of water, and those with body mass index greater than 30 kilograms per square meter will receive 10 centimeters of water. Ventilation will be maintained with a tidal volume of 6 milliliters per kilogram of ideal body weight throughout surgery.
Category
Other

2

Description
Control group: Patients will receive standard volume controlled mechanical ventilation with zero positive end expiratory pressure throughout surgery. Ventilator settings, including tidal volume of 6 milliliters per kilogram of ideal body weight, respiratory rate adjusted to maintain end tidal carbon dioxide between 35 and 40 millimeters of mercury, inspiratory to expiratory ratio of 1 to 2, and inspired oxygen fraction of 0.5, will be identical to the intervention group. No positive end expiratory pressure will be applied.
Category
Other

Recruitment centers

1

Recruitment center
Name of recruitment center
Iraqi Hospital
Full name of responsible person
Muslim Ghali Yousef
Street address
Iraqi hospital, Next to to Al-Furat Hospital, Sahla street, Kufa, Najaf
City
Kufa
Postal code
00964
Phone
+964 780 007 1097
Email
muslimghaly@gmail.com
Web page address
https://www.iraqsh.com/ar/contact-us/

Sponsors / Funding sources

1

Sponsor
Name of organization / entity
Shahid Beheshti University of Medical Sciences
Full name of responsible person
Seyed Ali Ziayi
Street address
Third floor, School of Medicine, next to Taleghani Hospital, Evin, Shahid Chamran Highway
City
Tehran
Province
Tehran
Postal code
19839-63113
Phone
+98 21 2254 9951
Email
mpd@sbmu.ac.ir
Grant name
Grant code / Reference number
Is the source of funding the same sponsor organization/entity?
No
Title of funding source
Shahid Beheshti University of Medical Sciences
Proportion provided by this source
100
Public or private sector
Public
Domestic or foreign origin
Domestic
Category of foreign source of funding
empty
Country of origin
Type of organization providing the funding
Academic

Person responsible for general inquiries

Contact
Name of organization / entity
Shahid Beheshti University of Medical Sciences
Full name of responsible person
Firoozeh Madadi
Position
Associate professor
Latest degree
Specialist
Other areas of specialty/work
Anesthesiology
Street address
Next to Shahid Beheshti University of Medical Sciences, Shahid A'rabi Street, Yemen Street, Shahid Chamran Highway
City
Tehran
Province
Tehran
Postal code
1983963113
Phone
+98 21 2303 1290
Email
fmadadi33@gmail.com

Person responsible for scientific inquiries

Contact
Name of organization / entity
Shahid Beheshti University of Medical Sciences
Full name of responsible person
Firoozeh Madadi
Position
Associate professor
Latest degree
Specialist
Other areas of specialty/work
Anesthesiology
Street address
Next to Shahid Beheshti University of Medical Sciences, Shahid A'rabi Street, Yemen Street, Shahid Chamran Highway
City
Tehran
Province
Tehran
Postal code
1983963113
Phone
+98 21 2303 1290
Email
fmadadi33@gmail.com

Person responsible for updating data

Contact
Name of organization / entity
Shahid Beheshti University of Medical Sciences
Full name of responsible person
Firoozeh Madadi
Position
Assistant professor
Latest degree
Specialist
Other areas of specialty/work
Anesthesiology
Street address
Next to Shahid Beheshti University of Medical Sciences, Shahid A'rabi Street, Yemen Street, Shahid Chamran Highway
City
Tehran
Province
Tehran
Postal code
1983963113
Phone
+98 21 2303 1290
Email
fmadadi33@gmail.com

Sharing plan

Deidentified Individual Participant Data Set (IPD)
Yes - There is a plan to make this available
Study Protocol
Yes - There is a plan to make this available
Statistical Analysis Plan
Yes - There is a plan to make this available
Informed Consent Form
Yes - There is a plan to make this available
Clinical Study Report
Yes - There is a plan to make this available
Analytic Code
Yes - There is a plan to make this available
Data Dictionary
Yes - There is a plan to make this available
Title and more details about the data/document
Data regarding ultrasonography of patients will be available.
When the data will become available and for how long
After data collection completion
To whom data/document is available
Other researchers
Under which criteria data/document could be used
Belonging to academic institution
From where data/document is obtainable
researcher's personal email fmadadi33@gmail.com
What processes are involved for a request to access data/document
Requesting by email
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