Oxygen Reserve Index (ORi) in Identifying Desaturation

February 15, 2026 updated by: Demet Altun, Istanbul University

The Role of Oxygen Reserve Index (ORi) in Identifying Early Desaturation During Endolaryngeal Surgery: A Randomized Clinical Trial

This randomized clinical trial investigates whether Oxygen Reserve Index (ORi) monitoring enables earlier detection of impending hypoxemia compared with conventional pulse oximetry during apneic intermittent ventilation in adult patients undergoing endolaryngeal surgery under general anesthesia. By providing continuous, noninvasive assessment of oxygen reserve in the hyperoxic range, ORi may offer an earlier warning of oxygen depletion before peripheral oxygen saturation declines. The study compares time to reventilation thresholds, arterial blood gas parameters, and perioperative respiratory outcomes between ORi-guided and standard SpO₂-guided monitoring strategies.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

This prospective, single-center, randomized clinical trial was designed to evaluate the role of the Oxygen Reserve Index (ORi) in the early detection of hypoxemia during apneic intermittent ventilation in adult patients undergoing elective endolaryngeal surgery under general anesthesia. Endolaryngeal procedures require shared airway management and frequently involve apneic periods, during which conventional pulse oximetry may fail to provide timely warning of declining oxygen reserves due to the plateau phase of the oxyhemoglobin dissociation curve. Eligible patients aged 18 years and older with ASA physical status I-III were randomly assigned to either an ORi-monitored group or a control group monitored with standard peripheral oxygen saturation (SpO₂). All patients underwent standardized anesthesia induction, preoxygenation, and apneic intermittent ventilation. In the ORi group, the threshold for resuming ventilation was defined as ORi reaching zero, whereas in the control group ventilation was resumed when SpO₂ decreased to 90%. The primary outcome was the time from the onset of apnea to the predefined reventilation threshold. Secondary outcomes included arterial blood gas parameters (pH, PaO₂, PaCO₂) at the time of reventilation, end-tidal carbon dioxide levels, perioperative lung ultrasound findings, post-anesthesia care unit length of stay, and postoperative respiratory outcomes. This study aims to determine whether ORi monitoring provides earlier and clinically meaningful warning of oxygen reserve depletion compared with conventional pulse oximetry, potentially improving patient safety during shared-airway surgery.

Study Type

Interventional

Enrollment (Estimated)

80

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 Contact

Study Contact Backup

Study Locations

  • Turkey (Türkiye)
    • Fatih
      • Istanbul, Fatih, Turkey (Türkiye), 34093
        • Istanbul University, Department of anesthesiology
        • Contact:

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:

  • Age 18 years or older
  • Scheduled for elective endolaryngeal surgery
  • Planned general anesthesia with apneic intermittent ventilation
  • American Society of Anesthesiologists (ASA) physical status I-III
  • Ability to provide written informed consent

Exclusion Criteria:

  • Age under 18 years
  • Preoperative chronic hypoxemia (baseline SpO₂ < 95%)
  • Patients transferred from the intensive care unit
  • ASA physical status IV or higher
  • Refusal or inability to provide informed consent

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: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Oxygen Reserve Index
Participants in this arm will undergo continuous Oxygen Reserve Index (ORi) monitoring in addition to standard anesthesia monitoring during general anesthesia with apneic intermittent ventilation for endolaryngeal surgery. ORi values will be used to guide the timing of reventilation, with reventilation initiated when ORi reaches zero, indicating depletion of oxygen reserve. Standard clinical care and anesthesia management will otherwise be identical to the control group.
Procedure: oxygen monitoring techniques
to determine whether ORi monitoring provides earlier and clinically meaningful warning of oxygen reserve depletion compared with conventional pulse oximetry, potentially improving patient safety during shared-airway surgery.
No Intervention: Peripheral oxygen saturation
Participants in this arm will receive standard anesthesia monitoring, including continuous peripheral oxygen saturation (SpO₂) monitoring, during general anesthesia with apneic intermittent ventilation for endolaryngeal surgery. The timing of reventilation will be guided by SpO₂ values, with reventilation initiated when SpO₂ decreases to 90%. All other aspects of anesthesia care and perioperative management will be identical to the experimental arm.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Time to Reventilation Threshold
Time Frame: From the onset of apnea until the predefined reventilation threshold is reached during the intraoperative period (within minutes).
Time from the onset of apnea to the predefined reventilation threshold, defined as Oxygen Reserve Index (ORi) reaching zero in the ORi group and peripheral oxygen saturation (SpO₂) decreasing to 90% in the control group, measured in seconds.
From the onset of apnea until the predefined reventilation threshold is reached during the intraoperative period (within minutes).

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Arterial Blood Gas Parameters at Reventilation
Time Frame: From the onset of apnea until the predefined reventilation threshold is reached during the intraoperative period (within minutes).
Arterial blood gas values including pH, partial pressure of oxygen (PaO₂), and partial pressure of carbon dioxide (PaCO₂) measured at the time of reventilation.
From the onset of apnea until the predefined reventilation threshold is reached during the intraoperative period (within minutes).
Perioperative Lung Ultrasound Findings
Time Frame: Preoperatively (before anesthesia induction) and postoperatively in the post-anesthesia care unit (within 1 hour after surgery).
Change in lung ultrasound (LUS) B-line count between preoperative and postoperative assessments.
Preoperatively (before anesthesia induction) and postoperatively in the post-anesthesia care unit (within 1 hour after surgery).
Postoperative Oxygenation
Time Frame: postoperatively in the post-anesthesia care unit (within 1 hour after surgery).
Lowest peripheral oxygen saturation (SpO₂) recorded during PACU stay.
postoperatively in the post-anesthesia care unit (within 1 hour after surgery).
End-Tidal Carbon Dioxide (EtCO₂) Level
Time Frame: During the apneic period, measured at the time of reventilation during surgery.
First recorded EtCO₂ value during apnea prior to reventilation.
During the apneic period, measured at the time of reventilation during surgery.

Collaborators and Investigators

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

Sponsor

Istanbul University

Investigators

  • Principal Investigator: ece naz demir, resident, Istanbul University
  • Study Director: demet altun, prof, Istanbul University

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 (Estimated)

January 27, 2026

Primary Completion (Estimated)

March 15, 2026

Study Completion (Estimated)

March 25, 2026

Study Registration Dates

First Submitted

January 27, 2026

First Submitted That Met QC Criteria

February 15, 2026

First Posted (Actual)

February 17, 2026

Study Record Updates

Last Update Posted (Actual)

February 17, 2026

Last Update Submitted That Met QC Criteria

February 15, 2026

Last Verified

January 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 2024/1568

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

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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