Effects of Minimal and Metabolic Flow Sevoflurane Anesthesia in Gynecological Surgery Patients

Comparative Analysis of Sevoflurane-Based Minimal and Metabolic Flow Anaesthesia: A Prospective Randomized Study in a Gynecological Surgery Patient Cohort

The aim of this study is to observe the effects of minimal and metabolically required basal anesthetic gas flow rates delivered by the anesthesia workstation under general anesthesia on body temperature, blood pressure, and heart rate during surgery.

It also aims to evaluate the impact of reducing excessive delivery of anesthetic gases, air, and oxygen beyond the patient's physiological needs during general anesthesia on minimizing the harmful effects of anesthetic gases on the environment, climate, and global warming, as well as on contributing positively to hospital costs.

Study Overview

• Status: Completed
• Conditions: Low-flow Anesthesia
• Intervention / Treatment: Procedure: Low Flow Anesthesia

Detailed Description

This prospective randomized study will be conducted in adult female patients undergoing elective gynecological surgery under general anesthesia. Following standard intravenous induction and endotracheal intubation, anesthesia will be maintained with sevoflurane using an advanced anesthesia workstation capable of delivering minimal and metabolic fresh gas flow rates.

After achieving the target anesthetic depth guided by minimum alveolar concentration (MAC) and MAC Brain monitoring, patients will be randomized to receive either minimal-flow (0.5 L/min) or metabolic-flow (0.3 L/min) fresh gas anesthesia. Randomization will be performed using an internet-based randomization tool.

Standard intraoperative monitoring will be applied in all patients, including electrocardiography, non-invasive blood pressure monitoring, pulse oximetry, capnography, anesthetic gas analysis, and esophageal temperature monitoring. Hemodynamic and respiratory parameters will be recorded at predefined time intervals throughout surgery. Sevoflurane consumption will be automatically calculated by the anesthesia workstation.

At the end of surgery, fresh gas flow will be increased to eliminate residual anesthetic gases, and patients will be extubated according to standard clinical criteria. Postoperative monitoring will continue in the post-anesthesia care unit.

The total study duration for each participant includes the intraoperative period and approximately 30 minutes of postoperative monitoring.

• Study Type: Observational
• Enrollment (Actual): 97

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Ankara, Turkey (Türkiye), 06490
    • Baskent University Ankara Hospital

Participation Criteria

Eligibility Criteria

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

• Sampling Method: Probability Sample

Study Population

Adult female patients scheduled for elective gynecologic surgery under general anesthesia at Baskent University Ankara Hospital.

Description

Inclusion Criteria:

• Female patients aged 18-65 years
• Undergoing elective gynecologic surgery under general anesthesia (including hysterectomy and/or oophorectomy)

Exclusion Criteria:

• Pregnant patients
• Patients with advanced cardiac disease
• Patients with advanced renal disease
• Patients with advanced hepatic disease
• Patients with advanced respiratory disease
• Severe obesity
• Heavy smokers
• Excessive alcohol consumption
• Known allergic sensitivity to halogenated anesthetic gases
• Use of medications that may interact with volatile anesthetics
• History of or susceptibility to malignant hyperthermia or neuromuscular disorders

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Minimal Flow Group (0.5 L/min); Participants will receive general anesthesia maintained with sevoflurane at a fresh gas flow rate of 0.5 L/min (minimal flow) after induction and achievement of target anesthetic concentration. Standard monitoring will be applied throughout surgery, including hemodynamic and respiratory parameters.	Procedure: Low Flow Anesthesia; Adjustment of fresh gas flow rates during general anesthesia using a modern anesthesia workstation (Getinge Flow-C). Patients will be randomized to receive anesthesia with either minimal flow (0.5 L/min) or metabolic flow (0.3 L/min). All other anesthetic agents and monitoring parameters will remain standardized according to institutional protocols.; Other Names: Metabolic Flow (0.3 L/min); Minimal Flow (0.5 L/min)
Metabolic Flow Group (0.3 L/min); Participants will receive general anesthesia maintained with sevoflurane at a fresh gas flow rate of 0.3 L/min (metabolic flow) after induction and achievement of target anesthetic concentration. Standard intraoperative monitoring will be applied as in the minimal flow group.	Procedure: Low Flow Anesthesia; Adjustment of fresh gas flow rates during general anesthesia using a modern anesthesia workstation (Getinge Flow-C). Patients will be randomized to receive anesthesia with either minimal flow (0.5 L/min) or metabolic flow (0.3 L/min). All other anesthetic agents and monitoring parameters will remain standardized according to institutional protocols.; Other Names: Metabolic Flow (0.3 L/min); Minimal Flow (0.5 L/min)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Core body temperature (°C)	Mean intraoperative core body temperature (Degrees Celsius (°C)): Measured intraoperatively using an esophageal temperature probe.	From induction of anesthesia until the end of surgery (approximately 1-2 hours)
Mean intraoperative heart rate (bpm)	Mean intraoperative heart rate (Beats per minute (bpm)): Measured intraoperatively via electrocardiographic monitoring.	From induction of anesthesia until the end of surgery (approximately 1-2 hours)
Mean intraoperative mean arterial pressure (mmHg)	Mean intraoperative mean arterial pressure (Millimeters of mercury (mmHg)): Measured intraoperatively using non-invasive blood pressure monitoring.	From induction of anesthesia until the end of surgery (approximately 1-2 hours)
Anesthetic gas consumption (mL)	Total sevoflurane consumption (Milliliters (mL)): As recorded by the anesthesia workstation.	From induction of anesthesia until the end of surgery (approximately 1-2 hours)
Richmond Agitation-Sedation Scale (RASS) (-5 to 4)	Richmond Agitation-Sedation Scale (RASS) (-5 to 4): The RASS is a 10-point scale ranging from -5 to +4. Negative scores (-1 to -5) indicate increasing levels of sedation, with -5 indicating an unarousable patient. Positive scores (+1 to +4) indicate increasing levels of agitation, with +4 indicating combative behavior. Scores closer to 0 reflect better recovery quality.	At the end of surgery / immediate postoperative period

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Anesthetic gas cost (USD or local currency)	Total intraoperative anesthetic gas cost (USD or local currency): Calculated based on total sevoflurane consumption recorded by the anesthesia workstation.	Intraoperative period - calculated at the end of surgery (1-2 hours).

Collaborators and Investigators

• Sponsor: Baskent University
• Investigators: Principal Investigator: Asude Ayhan, MD, Baskent University Ankara Hospital, Department of Anesthesiology and Reanimation

Study record dates

Study Major Dates

• Study Start (Actual): November 5, 2024
• Primary Completion (Actual): February 5, 2025
• Study Completion (Actual): February 5, 2025

Study Registration Dates

• First Submitted: February 26, 2026
• First Submitted That Met QC Criteria: March 9, 2026
• First Posted (Actual): March 11, 2026

Study Record Updates

• Last Update Posted (Actual): March 11, 2026
• Last Update Submitted That Met QC Criteria: March 9, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: KA 24/235; Baskent University (Other Identifier: Baskent University)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared. Only summarized results will be published in scientific journals or presented at conferences.

Drug and device information, study documents

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