Low-Flow Anesthesia Without Wash-in: Effects on Oxygenation and Depth of Anesthesia

April 10, 2026 updated by: Fazıl Ahmet Akbulut, MD, Erzincan Binali Yildirim Universitesi

Evaluation of the Safety of Low-Flow Anesthesia Initiated Without Wash-in in Terms of Oxygenation and Depth of Anesthesia Using Arterial Blood Gas Analysis and EEG-Based PSI Monitoring

This study aims to evaluate whether adjusting the fresh gas flow rate to low-flow immediately after intubation, without performing a wash-in, is a reliable approach with respect to depth of anesthesia and oxygenation.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Detailed Description

Low-flow anesthesia is defined as the delivery of fresh gas flow at a rate of 0.5-1 L/min on the anesthesia machine . Due to its advantages such as reducing costs, decreasing environmental pollution related to anesthetic gases, preserving mucociliary activity, softening secretions, and reducing heat loss, it has attracted considerable attention from anesthesiologists in recent years. However, the main concerns involve maintaining adequate ventilation, ensuring sufficient tissue oxygen delivery, and achieving adequate depth of anesthesia. Therefore, additional monitoring is required for the safe application of low-flow techniques. Exhaled gas volume, airway pressure, fraction of inspired oxygen (FiO₂), volatile anesthetic agent concentration, carbon dioxide concentration, and peripheral oxygen saturation (SpO₂) should be closely monitored. Arterial blood gas sampling is the gold standard for monitoring oxygenation. The Patient State Index (PSI) is a processed EEG index derived from frontal EEG signals that numerically expresses the level of anesthesia/sedation on a scale from 0 to 100. PSI is generated based on spectral and coherence analyses of data obtained from four-channel EEG monitors such as Masimo SedLine®, using advanced artifact filtering, and was developed for objective monitoring of the level of consciousness during general anesthesia. PSI values between 25 and 50 generally indicate an adequate depth of anesthesia, whereas higher values suggest a reduction in anesthetic depth.

In low-flow anesthesia, after induction the patient is connected to mechanical ventilation, and the volatile agent is adjusted to 1 MAC with 50% O₂. Subsequently, wash-in is achieved by administering fresh gas flow at 4-6 L/min for approximately 10 minutes, after which the flow is reduced. However, some studies have reported that initiating anesthesia maintenance directly with low fresh gas flow, without performing wash-in, may also be a feasible approach.

To date, no study has evaluated the reliability of initiating low fresh gas flow during mechanical ventilation without performing wash-in, using arterial blood gas analysis and PSI monitoring. This study aimed to compare the reliability of techniques involving reduction of fresh gas flow using the traditional wash-in method versus without wash-in, in terms of hypoxia and depth of anesthesia, using serial arterial blood gas measurements and PSI monitoring.

Study Type

Interventional

Enrollment (Estimated)

60

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Turkey (Türkiye)
    • Erzincan
      • Erzincan, Erzincan, Turkey (Türkiye), 24000
        • Binali Yildirim Univercity

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • ASA physical status I-II
  • Cases lasting longer than 30 minutes
  • Non-laparoscopic surgical procedures

Exclusion Criteria:

  • Patients with life-threatening renal, cardiac, or hepatic disease
  • Patients with chronic pulmonary diseases such as asthma or COPD
  • Patients with intraoperative hemodynamic instability
  • Patients with a body mass index (BMI) lower than 20 or higher than 30

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
No Intervention: Group WI
In this group, after intubation, patients were ventilated for 10 minutes with 4 L/min fresh gas flow consisting of 2% sevoflurane and 60% O₂, after which the fresh gas flow rate was reduced to 0.75 L/min
Active Comparator: Group WO
In this group, after intubation, the fresh gas flow rate was set to 0.75 L/min with 60% O₂. The sevoflurane vaporizer was initially set to 8%, and the sevoflurane concentration was subsequently reduced according to the MAC value
Device: Initiation of low-flow anesthesia without wash-in following intubation
After endotracheal intubation, fresh gas flow is set to 0.75 L/min with 60% O₂. The sevoflurane vaporizer is initially set to 8%, and the sevoflurane concentration is subsequently titrated according to the target MAC value. Anesthesia depth and oxygenation are monitored using PSI monitoring and serial arterial blood gas measurements.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Comparison of arterial oxygen partial pressure (PaO₂) values between groups
Time Frame: Measured at 10, 20, 30, and 45 minutes after induction of anesthesia and before the end of surgery.
Comparison of arterial oxygen partial pressure (PaO₂) and Patient State Index (PSI) values between groups.
Measured at 10, 20, 30, and 45 minutes after induction of anesthesia and before the end of surgery.
Comparison of Patient State Index (PSI) values between groups.
Time Frame: Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia.
PSI is an EEG-based index ranging from 0 to 100. Lower values indicate deeper anesthesia; the target range is 25-50 during general anesthesia.
Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Mean alveolar concentration (MAC) values
Time Frame: Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia.
Comparison of MAC values between groups during anesthesia maintenance.
Continuously monitored intraoperatively and recorded at 10, 20, 30, and 45 minutes after induction of anesthesia.
Total sevoflurane consumption
Time Frame: From induction of anesthesia until the end of surgery (average duration approximately X minutes).
Comparison of total sevoflurane consumption between groups.
From induction of anesthesia until the end of surgery (average duration approximately X minutes).
Time to reach target MAC level
Time Frame: Time (minutes) from completion of endotracheal intubation to achievement of MAC 1.0, as measured on the anesthesia monitor
Time required to achieve target MAC level after intubation
Time (minutes) from completion of endotracheal intubation to achievement of MAC 1.0, as measured on the anesthesia monitor

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Erzincan Binali Yildirim Universitesi

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

March 1, 2026

Primary Completion (Estimated)

July 1, 2026

Study Completion (Estimated)

August 1, 2026

Study Registration Dates

First Submitted

March 29, 2026

First Submitted That Met QC Criteria

April 10, 2026

First Posted (Actual)

April 16, 2026

Study Record Updates

Last Update Posted (Actual)

April 16, 2026

Last Update Submitted That Met QC Criteria

April 10, 2026

Last Verified

April 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • ErzincanBinaliYildirim

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

PO2, PCO2, PSI, Sevoflurane consumption, Demographic data

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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