Effect of Trendelenburg Position on Patient State Index

Effect of the Trendelenburg Position on Patient State Index and Frontal Cerebral Oxygenation: A Prospective Observational Study

The goal of this observational study is to evaluate whether the Trendelenburg position affects electroencephalography-based depth of anesthesia monitoring and cerebral oxygenation during general anesthesia.

The main questions it aims to answer are:

• Does the Trendelenburg position cause a change in the Patient State Index (PSI), an Electroensephalography (EEG)-derived indicator of anesthetic depth?
• Are changes in PSI associated with changes in frontal cerebral oxygen saturation (rSO₂) and hemodynamic parameters?

The study will include adult female patients undergoing elective laparoscopic gynecologic surgery under general anesthesia.

Participants will receive standard anesthesia and routine intraoperative monitoring. In addition to standard monitoring, Patient State Index (PSI) and frontal cerebral oxygen saturation (rSO₂) will be recorded using non-invasive sensors. No additional intervention will be performed for research purposes.

Physiological parameters including PSI, cerebral oxygen saturation, mean arterial pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide will be recorded at predefined intraoperative time points before and after the Trendelenburg position.

The study aims to determine whether position-related physiological changes influence EEG-based anesthesia depth indices and to improve the interpretation of intraoperative brain monitoring.

Study Overview

• Status: Not yet recruiting
• Conditions: Laparoscopic Hysterectomy

Detailed Description

Electroencephalography (EEG)-based depth of anesthesia monitors are widely used to assess the hypnotic component of general anesthesia. The Patient State Index (PSI) is a processed EEG parameter derived from frontal EEG signals and provides a numerical estimate of anesthetic depth ranging from 0 to 100. Although these indices are primarily designed to reflect the pharmacologic effects of anesthetic agents, physiological factors that influence cerebral hemodynamics may also affect EEG-derived parameters.

The Trendelenburg position is frequently used during laparoscopic pelvic surgery to improve surgical exposure. This position can alter venous return, increase cerebral venous pressure, and influence intracranial dynamics. When combined with pneumoperitoneum, these physiological changes may modify cerebral blood flow and cerebral oxygenation. Such alterations may potentially influence EEG-based indices of anesthetic depth independently of anesthetic drug concentration.

Previous studies have demonstrated that body position can influence processed EEG indices such as the bispectral index (BIS), particularly in the beach-chair position. However, the response of the Patient State Index to the Trendelenburg position has not been clearly established.

This prospective observational study aims to evaluate whether the Trendelenburg position affects PSI values during general anesthesia and to investigate the relationship between PSI changes and cerebral oxygenation measured by near-infrared spectroscopy (NIRS).

Adult female patients undergoing elective laparoscopic hysterectomy under general anesthesia will be included. Standard intraoperative monitoring will be applied, including electrocardiography, non-invasive blood pressure, pulse oximetry, end-tidal carbon dioxide, and anesthetic gas monitoring. In addition, EEG-based depth of anesthesia monitoring will be performed using the PSI monitor (Masimo SedLine), and frontal cerebral oxygen saturation (rSO₂) will be measured using near-infrared spectroscopy sensors.

Physiological parameters including PSI, cerebral oxygen saturation, mean arterial pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide will be recorded at predefined intraoperative time points: before induction of anesthesia, after tracheal intubation in the supine position, after pneumoperitoneum, and at several intervals following the Trendelenburg position.

No intervention will be performed for research purposes. Anesthetic management and surgical positioning will follow routine clinical practice. The study will analyze whether position-related physiological changes are associated with variations in PSI and whether these changes correlate with cerebral oxygenation or hemodynamic parameters.

Understanding the influence of patient positioning on EEG-based anesthesia depth indices may improve the interpretation of intraoperative brain monitoring and help prevent unnecessary adjustments of anesthetic drug dosing.

• Study Type: Observational
• Enrollment (Estimated): 60

Contacts and Locations

• Study Contact: Name: Ayca Tas Tuna, Professor, M.D.; Phone Number: +90 532 300 48 26; Email: aycatas@yahoo.com
• Study Contact Backup: Name: Ahmet R Dogan, M.D.; Phone Number: +905427988070

Participation Criteria

Eligibility Criteria

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

• Sampling Method: Non-Probability Sample

Study Population

The study population consists of adult female patients undergoing elective laparoscopic hysterectomy under general anesthesia at a tertiary care university-affiliated hospital. Eligible patients will be recruited consecutively among those scheduled for surgery who meet the inclusion criteria and provide written informed consent.

Description

Inclusion Criteria:

• Female patients aged 18-65 years
• American Society of Anesthesiologists (ASA) physical status I-III
• Scheduled for elective laparoscopic hysterectomy under general anesthesia
• Ability to provide written informed consent

Exclusion Criteria:

• History of neurological disease (e.g., stroke, epilepsy)
• Known cerebrovascular disease, glaucoma, or retinal disease
• Severe cardiac or pulmonary disease
• Contraindication to near-infrared spectroscopy sensor placement
• Obesity (Body Mass Index > 35 kg/m²)

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Patients Undergoing Laparoscopic Hysterectomy in Trendelenburg Position; This cohort includes adult female patients undergoing elective laparoscopic hysterectomy under general anesthesia. All participants receive standard intraoperative monitoring as part of routine clinical care. In addition to routine monitoring, depth of anesthesia is assessed using the Patient State Index (PSI), and frontal cerebral oxygen saturation (rSO₂) is measured using near-infrared spectroscopy sensors. Physiological parameters including PSI, cerebral oxygen saturation, mean arterial pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide are recorded at predefined intraoperative time points before and after pneumoperitoneum and Trendelenburg positioning. No intervention is performed for research purposes. Surgical positioning and anesthetic management follow routine clinical practice, and the study involves only the observational recording of physiological parameters.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Patient State Index (ΔPSI) After Trendelenburg Position	The primary outcome is the change in Patient State Index (PSI), an Electroensephalography(EEG)-derived indicator of anesthetic depth, between the supine position after tracheal intubation and the early Trendelenburg position following pneumoperitoneum. PSI values will be recorded using the Masimo SedLine monitoring system. The analysis will evaluate whether Trendelenburg positioning is associated with a significant change in PSI independent of anesthetic drug concentration.	From Post-intubation (Supine) to Trendelenburg Positioning

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in Frontal Cerebral Oxygen Saturation (rSO₂)	Frontal cerebral oxygen saturation (rSO₂) measured using near-infrared spectroscopy sensors will be recorded to evaluate changes in cerebral oxygenation associated with pneumoperitoneum and Trendelenburg positioning. The analysis will assess whether changes in rSO₂ occur during Trendelenburg positioning and whether these changes are associated with variations in Patient State Index (PSI).	Intraoperative period (recorded at predefined time points before and after Trendelenburg positioning)
Mean Arterial Pressure Changes During Trendelenburg Position	Mean arterial pressure (MAP) will be recorded to evaluate hemodynamic changes associated with pneumoperitoneum and Trendelenburg positioning and to explore its relationship with changes in Patient State Index and cerebral oxygen saturation.	Intraoperative period (recorded at predefined time points before and after Trendelenburg positioning)
Heart Rate Changes During Trendelenburg Position	Heart rate will be monitored to evaluate intraoperative hemodynamic responses associated with pneumoperitoneum and Trendelenburg positioning and to assess its relationship with changes in Patient State Index and cerebral oxygen saturation.	Intraoperative period (recorded at predefined time points before and after Trendelenburg positioning)

Collaborators and Investigators

• Sponsor: Sakarya University
• Investigators: Principal Investigator: AYÇA TAŞ TUNA, Professor, M.D., Sakarya University Faculty of Medicine

Publications and helpful links

General Publications

• Buget MI, Atalar AC, Edipoglu IS, Sungur Z, Sivrikoz N, Karadeniz M, Saka E, Kucukay S, Senturk MN. Patient state index and cerebral blood flow changes during shoulder arthroscopy in beach chair position. Braz J Anesthesiol. 2016 Sep-Oct;66(5):470-4. doi: 10.1016/j.bjane.2015.02.002. Epub 2015 Oct 1.
• Chen W, Wang J, Wang L, Hu W, Chen X, Jin L. Effect of patient position on the EEG bispectral index and entropy index under general anaesthesia. Technol Health Care. 2025;33(1):311-319. doi: 10.3233/THC-241026.

Study record dates

Study Major Dates

• Study Start (Estimated): April 1, 2026
• Primary Completion (Estimated): July 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: March 9, 2026
• First Submitted That Met QC Criteria: March 9, 2026
• First Posted (Actual): March 12, 2026

Study Record Updates

• Last Update Posted (Actual): March 13, 2026
• Last Update Submitted That Met QC Criteria: March 11, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: General Anesthesia; Cerebral Oxygenation; Depth of Anesthesia Monitoring; Intraoperative Monitoring; Near-Infrared Spectroscopy; Trendelenburg Position; Patient State Index; Processed EEG
• Other Study ID Numbers: SEAH-TrendelenburgPsi-2026

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be publicly shared because the dataset contains clinical perioperative monitoring data collected at a single center. De-identified data may be made available from the corresponding investigator upon reasonable request and subject to institutional and ethical approval.

Drug and device information, study documents

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