Hyperoxemia and Oxygen Reserve Index During Neurointerventional Anesthesia

September 30, 2026 updated by: Cansu Ofluoğlu, Fatih Sultan Mehmet Training and Research Hospital

Arterial Hyperoxemia and Oxygen Reserve Index During Elective Neurointerventional Procedures Under General Anesthesia: A Prospective Observational Study

The goal of this observational study is to learn how often high blood oxygen levels (hyperoxemia) occur in adults receiving general anesthesia for planned (elective) neurointerventional procedures, such as brain aneurysm coiling or other catheter-based treatments of brain vessels. It will also look at how well a non-invasive finger sensor measurement called the Oxygen Reserve Index (ORi) reflects arterial oxygen levels.

The main questions it aims to answer are:

  • How often is the arterial oxygen pressure (PaO2) 150 mmHg or higher in blood gas samples taken as part of routine care during these procedures?
  • How does ORi relate to PaO2, and can ORi help identify high oxygen levels?

Participants will:

  • Receive anesthesia and their procedure exactly as planned by their care team; the study does not change any treatment, oxygen setting, or ventilator setting.
  • Have a painless ORi sensor placed on a finger, similar to a standard pulse oximeter, during anesthesia.
  • Have their routine monitoring values and the results of arterial blood gas samples taken for routine clinical care recorded.

No extra blood samples will be taken for the study, and ORi values will not be used to guide care.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

Background and rationale:

Oxygen is routinely given during general anesthesia to prevent hypoxemia. However, oxygen given beyond the patient's needs may cause arterial hyperoxemia, which has been linked to vasoconstriction, oxidative stress, and absorption atelectasis. Normobaric hyperoxia has been shown to reduce cerebral blood flow, and cumulative hyperoxemia exposure has been associated with unfavorable outcomes in ventilated patients with aneurysmal subarachnoid hemorrhage. Although these findings come from critically ill populations, they provide a physiological rationale for describing arterial oxygen levels in patients undergoing elective neurointerventional procedures, in whom maintaining cerebral perfusion is essential.

Standard pulse oximetry (SpO2) plateaus at high arterial oxygen levels and cannot detect hyperoxemia. The Oxygen Reserve Index (ORi) is a continuous, non-invasive, dimensionless index (0 to 1) derived from multi-wavelength pulse co-oximetry, reported to reflect oxygenation changes in the moderately hyperoxic range (approximately PaO2 100-200 mmHg). The ORi-PaO2 relationship varies across populations and clinical settings, and it has not been described in stable adults undergoing elective neurointerventional procedures under general anesthesia.

Study design:

This is a single-center, prospective, observational study conducted at the Department of Anesthesiology and Reanimation and the Interventional Radiology Unit of University of Health Sciences Fatih Sultan Mehmet Training and Research Hospital, Istanbul, Türkiye. No randomization, group allocation, or clinical intervention will be performed.

Procedures:

Anesthesia induction and maintenance, ventilator settings, FiO2, fluids, vasoactive drugs, and all other management will follow the attending anesthesiologist's routine practice. In addition to standard monitoring, an ORi-capable pulse co-oximetry sensor will be applied. ORi values will be recorded by the investigator but will not be used for clinical decision-making, and no changes in FiO2, ventilation, or treatment will be made based on ORi.

ORi, SpO2, FiO2, heart rate, mean arterial pressure, end-tidal carbon dioxide, body temperature, perfusion index, and signal quality will be recorded at the following time points: 5 minutes after intubation and initiation of mechanical ventilation (T1), 30 minutes (T2) and 60 minutes (T3) after the start of the procedure, every 60 minutes thereafter starting at 120 minutes if the procedure continues (T4 onward), and at the end of the procedure before FiO2 is increased for emergence (Tend).

Whenever an arterial blood gas sample is drawn by the clinical team for routine care, PaO2, PaCO2, pH, SaO2, hemoglobin, and lactate will be recorded and matched with ORi, SpO2, FiO2, perfusion index, and hemodynamic values recorded at the time of sampling or within 1 minute. No additional blood samples will be drawn for research purposes, and the timing and number of routine samples will not be altered.

Patients without a routine arterial blood gas will remain in the cohort for descriptive analyses; PaO2-based analyses will include all valid matched ORi-PaO2 pairs.

Sample size and statistical analysis:

Assuming an expected hyperoxemia proportion of 50%, a 95% confidence level, and a precision of +/-10%, the minimum required sample size is 96 patients; 100 patients will be enrolled to account for missing data. The proportion of matched measurements with PaO2 >=150 mmHg will be reported with 95% confidence intervals. Repeated measurements will be analyzed with mixed-effects models. The ORi-PaO2 relationship, including possible nonlinearity and plateau behavior, will be evaluated with appropriate regression models. The ability of ORi to discriminate PaO2 >=150 and >=200 mmHg will be explored with ROC analysis, accounting for within-patient clustering. A p value <0.05 will be considered statistically significant.

Data protection:

All data will be de-identified, recorded on study case report forms, and used by the study team for scientific purposes only.

Study Type

Observational

Enrollment (Estimated)

100

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 Locations

  • Turkey (Türkiye)
      • Istanbul, Turkey (Türkiye), 34000
        • University of Health Sciences Fatih Sultan Mehmet Training and Research Hospital Scientific Research
        • 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

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Sampling Method

Non-Probability Sample

Study Population

Adult patients (ASA I-III) scheduled for elective neurointerventional procedures under general anesthesia with routine invasive arterial monitoring at the Interventional Radiology Unit of University of Health Sciences Fatih Sultan Mehmet Training and Research Hospital, Istanbul, Türkiye. Eligible patients will be enrolled consecutively.

Description

Inclusion Criteria:

  • Age 18 years or older
  • American Society of Anesthesiologists (ASA) physical status I-III
  • Scheduled for an elective neurointerventional procedure
  • Procedure performed under general anesthesia
  • Invasive arterial pressure monitoring and arterial blood gas sampling planned as part of routine clinical care
  • Written informed consent obtained from the patient or, when required, the legal representative

Exclusion Criteria:

  • Refusal to participate
  • Emergency neurointerventional procedure
  • ASA physical status IV or higher
  • Pregnancy
  • Mechanical ventilation before the procedure
  • Chronic respiratory failure requiring long-term home oxygen therapy
  • Severe peripheral circulatory impairment or technical signal failure preventing reliable ORi measurement

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

  • Observational Models: COHORT
  • Time Perspectives: PROSPECTIVE

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Elective Neurointerventional Procedures Under General Anesthesia

Adult patients (ASA I-III) undergoing elective neurointerventional procedures under general anesthesia with routine invasive arterial pressure monitoring. All anesthetic, ventilatory, and oxygen management follows routine clinical practice. An ORi-capable pulse co-oximetry sensor is applied for observational recording only; ORi values are not used for clinical decisions. Routine monitoring data and results of arterial blood gas samples drawn for clinical care are recorded. No additional blood samples are taken for research purposes.
Other: Oxygen Reserve Index Monitoring (Observational)

Non-invasive ORi measurement via multi-wavelength pulse co-oximetry, recorded blinded to the anesthesia team and not used to guide care.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Proportion of Matched Arterial Blood Gas Measurements With PaO2 >=150 mmHg
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Number of valid matched ORi-PaO2 measurement pairs with PaO2 >=150 mmHg divided by the total number of valid matched pairs, multiplied by 100. Only arterial blood gas samples drawn for routine clinical care and matched to a valid ORi value recorded at the time of sampling or within 1 minute are included. Reported with 95% confidence interval.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Proportion of Matched Arterial Blood Gas Measurements With PaO2 >=200 mmHg
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Number of valid matched ORi-PaO2 pairs with PaO2 >=200 mmHg divided by the total number of valid matched pairs, multiplied by 100, reported with 95% confidence interval.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Proportion of Patients With at Least One PaO2 >=150 mmHg and >=200 mmHg Measurement
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Percentage of patients with at least one valid matched arterial blood gas measurement showing PaO2 >=150 mmHg, and separately >=200 mmHg, among patients with at least one valid matched measurement.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Per-Patient Proportion of Hyperoxemic Measurements
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

For each patient, the number of matched measurements with PaO2 >=150 mmHg (and >=200 mmHg) divided by that patient's total number of matched measurements, summarized across patients.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Perioperative Changes in ORi, SpO2, FiO2, and Hemodynamic Parameters
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

ORi (dimensionless, 0-1), SpO2 (%), FiO2 (%), heart rate (beats/min), mean arterial pressure (mmHg), end-tidal CO2 (mmHg), body temperature (degrees C), and perfusion index recorded at T1 (5 min after intubation), T2 (30 min), T3 (60 min), every 60 min thereafter from 120 min, and Tend (end of procedure before FiO2 increase). Changes over time analyzed with mixed-effects models.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Relationship Between ORi and PaO2
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Association between ORi and PaO2 in matched measurement pairs, evaluated with linear and nonlinear regression models accounting for repeated measurements within patients, including assessment of a possible plateau in ORi at higher PaO2 values.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Discriminative Ability of ORi for PaO2 >=150 mmHg and >=200 mmHg
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Area under the receiver operating characteristic curve (AUROC) of ORi for detecting PaO2 >=150 mmHg and >=200 mmHg in matched pairs, with optimal cut-off, sensitivity, and specificity. Exploratory analysis accounting for within-patient clustering.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)
Factors Associated With Hyperoxemia
Time Frame: Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Association of hyperoxemia (PaO2 >=150 mmHg) with patient characteristics (age, sex, body mass index, ASA class, comorbidities), anesthesia characteristics (FiO2, anesthesia duration), and procedure characteristics (procedure type, duration, contrast volume), evaluated with multivariable mixed-effects models.
Intraoperative period, from intubation to the end of the procedure before FiO2 is increased for emergence (approximately 1-4 hours)

Collaborators and Investigators

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

Sponsor

Fatih Sultan Mehmet Training and Research Hospital

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)

October 1, 2026

Primary Completion (Estimated)

April 1, 2027

Study Completion (Estimated)

April 1, 2027

Study Registration Dates

First Submitted

September 30, 2026

First Submitted That Met QC Criteria

September 30, 2026

First Posted (Actual)

October 6, 2026

Study Record Updates

Last Update Posted (Actual)

October 6, 2026

Last Update Submitted That Met QC Criteria

September 30, 2026

Last Verified

September 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • FSM-ORİ-ANGİO-2026
  • 2026/09-80 (Other Identifier: University of Health Sciences Fatih Sultan Mehmet Training and Research Hospital Scientific Research Ethics Committee)

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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