Effects of Standard and Modified Z-Trendelenburg Positions on Cerebral Oxygenation and Optic Nerve Sheath Diameter (MOD-TREND)

Comparison of the Effects of Standard Trendelenburg and Modified Z Trendelenburg Positions on Cerebral Oxygenation (NIRS) and Optic Nerve Sheath Diameter in Laparoscopic Gynecological Cases

The purpose of this study is to compare the effects of the standard Trendelenburg position and the modified Z-Trendelenburg position on cerebral oxygenation and optic nerve sheath diameter (ONSD) in patients undergoing laparoscopic surgery. The prolonged use of the standard Trendelenburg position combined with pneumoperitoneum can increase intracranial pressure and affect cerebral blood flow. In this study, researchers will use non-invasive methods, including Near-Infrared Spectroscopy (NIRS) to monitor regional cerebral oxygenation, and ocular ultrasonography to measure ONSD as an indicator of intracranial pressure changes. The main goal is to determine whether the modified Z-Trendelenburg position serves as a safer physiological alternative by reducing these potential adverse effects compared to the standard position.

Study Overview

• Status: Completed
• Conditions: Laparoscopic Gynecological Surgery
• Intervention / Treatment: Procedure: Standard Trendelenburg Position; Procedure: Modified Z-Trendelenburg Position

Detailed Description

Laparoscopic surgeries frequently require patients to be placed in a steep Trendelenburg position with pneumoperitoneum to provide optimal surgical exposure. However, this combination induces significant physiological alterations, most notably an increase in intracranial pressure (ICP) and a potential compromise in cerebral venous drainage and regional cerebral oxygen saturation (rSO2). Non-invasive monitoring techniques, such as measuring the optic nerve sheath diameter (ONSD) via ultrasonography, provide reliable, real-time estimates of ICP changes. Additionally, Near-Infrared Spectroscopy (NIRS) allows for the continuous monitoring of cerebral oxygenation.

This prospective clinical study is designed to evaluate and compare the cerebral and hemodynamic impacts of the standard straight Trendelenburg position versus a modified Z-Trendelenburg position. Participants scheduled for elective laparoscopic procedures will be divided into specific positioning groups. Hemodynamic parameters, NIRS values, and ONSD measurements will be recorded at predefined time points throughout the surgery: at baseline, post-induction, after the establishment of pneumoperitoneum and positioning, at specific intervals during the surgery, and post-operatively in the recovery room. The primary hypothesis is that the modified Z-Trendelenburg position will attenuate the rise in ICP (reflected by a smaller increase in ONSD) and provide better cerebral oxygenation stability compared to the traditional standard position.

• Study Type: Observational
• Enrollment (Actual): 70

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Ankara
    • Ankara, Ankara, Turkey (Türkiye), 06010
      • Ankara Etlik City Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

The study population consists of adult patients up to 80 years of age who [are admitted to the intensive care unit / are undergoing elective surgery / present to the emergency department]. The population excludes patients with known increased intracranial pressure, severe cerebrovascular, cardiovascular, or pulmonary diseases, morbid obesity (BMI > 35 kg/m^2), pregnancy, and any pre-existing ocular pathologies that could affect optic nerve sheath diameter (ONSD)

Description

Inclusion Criteria:

Patients aged between 18 and 70 years

American Society of Anesthesiologists (ASA) physical status I or II

Scheduled for elective laparoscopic surgery requiring Trendelenburg position

Provided written informed consent

Exclusion Criteria:

Patient refusal to participate

History of severe cerebrovascular disease

Known increased intracranial pressure

Pre-existing ocular pathology that could affect optic nerve sheath diameter (ONSD) measurements (e.g., glaucoma, optic neuritis, ocular trauma)

Severe cardiovascular or pulmonary disease Body Mass Index (BMI) greater than 35 kg/m^2 Pregnancy

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Standard Trendelenburg Cohort; Patients undergoing elective laparoscopic surgery placed in the standard straight Trendelenburg position.	Procedure: Standard Trendelenburg Position; Placement of the patient in the traditional straight head-down tilt position required for laparoscopic surgical access and pneumoperitoneum
Modified Z-Trendelenburg Cohort; Patients undergoing elective laparoscopic surgery placed in the modified Z-Trendelenburg position (head-down tilt combined with leg flexion).	Procedure: Modified Z-Trendelenburg Position; Placement of the patient in a modified head-down tilt position combined with leg flexion

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Regional Cerebral Oxygen Saturation (rSO2)	Regional cerebral oxygen saturation (rSO2) will be measured bilaterally using Near-Infrared Spectroscopy (NIRS) sensors placed on the patient's forehead. This non-invasive monitoring will be used to evaluate cerebral oxygenation changes during different surgical positions and pneumoperitoneum. Values will be recorded as percentages (%).	Baseline (before anesthesia induction), at 10, 45, 60, and 90 minutes after establishing pneumoperitoneum and surgical positioning, and 10 minutes after returning to the supine position.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Mean Arterial Pressure (MAP)	Mean Arterial Pressure (MAP) will be continuously monitored and recorded to evaluate the cardiovascular effects of the pneumoperitoneum and modified positioning. Values will be reported in mmHg.	Baseline ( 10 minutes after anesthesia induction), at 10,45, 60, and 90 minutes after establishing pneumoperitoneum and surgical positioning, and 10 minutes after returning to the supine position.
Change in Optic Nerve Sheath Diameter (ONSD)	Intracranial pressure changes will be evaluated indirectly by measuring the optic nerve sheath diameter (ONSD) using ocular ultrasonography. Measurements will be taken bilaterally and recorded in millimeters (mm).	Baseline ( 10 minutes after anesthesia induction), at 10, 45, 60, and 90 minutes after establishing pneumoperitoneum and surgical positioning, and 10 minutes after returning to the supine position.
Change in Peak Airway Pressure (Ppeak)	Peak airway pressure will be monitored continuously and recorded to evaluate the effects of pneumoperitoneum and different surgical positions on respiratory mechanics. Values will be reported in centimeters of water (cmH2O).	Baseline (10 minutes after anesthesia induction), at 10,45, 60, and 90 minutes after establishing pneumoperitoneum and surgical positioning, and 10 minutes after returning to the supine posi
Change in End-tidal Carbon Dioxide (EtCO2)	End-tidal carbon dioxide levels will be monitored continuously via capnography to evaluate ventilation status during pneumoperitoneum and different positioning. Values will be reported in millimeters of mercury (mmHg).	Baseline (10 minutes after anesthesia induction), at 10, 45, 60, and 90 minutes after establishing pneumoperitoneum and surgical positioning, and 10 minutes after returning to the supine positi

Collaborators and Investigators

• Sponsor: Ankara Etlik City Hospital

Study record dates

Study Major Dates

• Study Start (Actual): March 6, 2026
• Primary Completion (Actual): May 18, 2026
• Study Completion (Actual): May 18, 2026

Study Registration Dates

• First Submitted: May 18, 2026
• First Submitted That Met QC Criteria: June 2, 2026
• First Posted (Actual): June 8, 2026

Study Record Updates

• Last Update Posted (Actual): June 8, 2026
• Last Update Submitted That Met QC Criteria: June 2, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Laparoscopic surgery; Pneumoperitoneum; Optic Nerve Sheath Diameter; Cerebral Oxygenation; Intracranial Pressure; Trendelenburg position; Near-Infrared Spectroscopy; Modified Z-Trendelenburg
• Additional Relevant MeSH Terms: Digestive System Diseases; Peritoneal Diseases; Pneumoperitoneum
• Other Study ID Numbers: AEŞH-EK-2026-048

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: The study population consists of adult female patients, aged 18 to 80 years, classified with an American Society of Anesthesiologists (ASA) physical status of I or II, who are scheduled to undergo elective laparoscopic gynecological surgery under general anesthesia at Ankara Etlik City Hospital. Eligible participants must have a Body Mass Index (BMI) between 18 and 30 kg/m2 and require the Trendelenburg position during surgery. Patients are excluded from the study population if they have a history of intracranial pathology, neurological disorders, severe ophthalmologic conditions (such as glaucoma), cerebrovascular diseases, severe cardiac or pulmonary diseases, profound anemia (Hb < 10 g/dL), or if they are pregnant.

Drug and device information, study documents

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