Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood GasNCT07921849
"Comparison of Oxygen Reserve Index (ORI), End-Tidal Oxygen, and Time-Based Preoxygenation Targets With Arterial Blood Gas During Preoxygenation
An observational study of Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas, run by Kocaeli City Hospital.
Trial summary
The goal of this observational study is to learn how well different preoxygenation targets reflect the actual amount of oxygen in the blood in adults having planned surgery under general anesthesia. Read more about this study
- Who is it for?
- Ages 18 to 75 yearsHealthy volunteers can take part
- Conditions the study is for
- Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas
- How many people
- 30 participants
- Where
- No sites listed yet
- Study dates
- 1 Dec 2026to 1 Jun 2027
- Phase
- Observational
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 75 years
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Study population: The study population will consist of adult patients undergoing elective surgery of any surgical specialty under general anesthesia with endotracheal intubation at the Department of Anesthesiology and Reanimation, Kocaeli City Hospital, Izmit, Turkey. Only patients in whom invasive arterial cannulation is clinically indicated as part of their routine anesthetic management will be approached, for example because of the type and expected duration of surgery, anticipated blood loss or hemodynamic changes, the need for repeated blood gas analysis, or patient comorbidities. Arterial cannulation will not be performed for research purposes. Eligible patients will be identified during the preoperative anesthesia assessment and enrolled consecutively after written informed consent is obtained.
Who may be able to join
- Age 18-75 years
- ASA physical status I-III
- Scheduled for elective surgery
- Planned general anesthesia with endotracheal intubation
- Invasive arterial cannulation planned for clinical reasons
- Suitable for ORI measurement with an appropriate sensor
- Able to provide written informed consent
Who cannot join
- Emergency surgery
- SpO2 below 94% on room air
- Advanced chronic obstructive pulmonary disease (COPD) or severe restrictive lung disease
- Hemodynamic instability
- Severe peripheral circulatory disorder
- Inadequate ORI signal quality
Show all 11Show fewer
- Significant mask leak
- Hemoglobin below 8 g/dL
- Suspected methemoglobinemia or carboxyhemoglobinemia, or a related hemoglobinopathy
- Pregnancy
- Failure to obtain data according to the protocol, missing data, or withdrawal of consent
Trial locations and contacts
No sites are listed yet. Contact the study team or a site near you to ask about taking part.
About this study
Official title: "Comparison of Oxygen Reserve Index (ORI), End-Tidal Oxygen, and Time-Based Preoxygenation Targets With Arterial Blood Gas During Preoxygenation: A Prospective Cross-Over Study"
The goal of this observational study is to learn how well different preoxygenation targets reflect the actual amount of oxygen in the blood in adults having planned surgery under general anesthesia. Preoxygenation means breathing pure oxygen through a face mask before going to sleep, so that the body has an oxygen reserve while the breathing tube is placed.
Doctors usually decide that preoxygenation is adequate either after 3 minutes of breathing oxygen or when the oxygen level in exhaled air (end-tidal oxygen, EtO2) reaches 90% or more. A newer finger sensor measures the Oxygen Reserve Index (ORI), a noninvasive number that may show oxygen reserve continuously. However, it is not clear how closely these targets match the oxygen level measured directly in arterial blood (PaO2).
Read more
The main questions this study aims to answer are whether the arterial oxygen level (PaO2) differs when ORI reaches 0.45, when EtO2 reaches 90%, and at the 3rd minute of preoxygenation, and whether an ORI value of 0.45 or higher reflects an adequate arterial oxygen reserve.
Participants who already need an arterial line for their surgery will breathe 100% oxygen through a tight-fitting face mask for up to 5 minutes before anesthesia induction. Small blood samples will be taken from the existing arterial line at each target point. No additional invasive procedure will be done for the study.
Read the detailed description
Preoxygenation before induction of general anesthesia increases pulmonary oxygen stores by replacing nitrogen in the functional residual capacity with oxygen, thereby prolonging the safe apnea time during airway management. In clinical practice, preoxygenation adequacy is commonly judged by a fixed duration (3 minutes of tidal volume breathing) or by an end-tidal oxygen fraction (EtO2) of 90% or higher. Neither target directly or continuously reflects arterial oxygenation in every patient.
The Oxygen Reserve Index (ORI) is a relative, dimensionless index (0 to 1) derived from multi-wavelength pulse co-oximetry. It is intended to track changes in oxygen reserve noninvasively in the mild-to-moderate hyperoxic range, where SpO2 plateaus. ORI thresholds depend on the device algorithm and sensor generation; with the updated algorithm, an ORI cut-off of 0.45 has been reported for PaO2 of 150 mmHg or higher. Prospective data that compare ORI, EtO2 and time-based preoxygenation targets against simultaneous arterial blood gas measurements in the same patient are limited.
This is a prospective, single-center, observational study with a repeated-measures design, in which each patient serves as their own control. It is planned as a pilot study of 30 patients. Adult patients (18-75 years, ASA I-III) scheduled for elective surgery under general anesthesia with endotracheal intubation, who require invasive arterial cannulation for clinical reasons, will be enrolled after written informed consent. Arterial cannulation will not be performed for research purposes.
Standard monitoring will include ECG, noninvasive and invasive arterial blood pressure, heart rate, SpO2, EtO2/EtCO2 (anesthesia machine gas analyzer), and ORI (Masimo multi-wavelength pulse co-oximetry), with perfusion index (PI) and pleth variability index (PVI) when available. The ORI sensor will be placed on the same finger (left fourth finger) throughout the measurements. Factors affecting the optical signal, such as nail polish, ambient light, motion and improper placement, will be controlled. ORI values will be recorded only after a stable plethysmographic waveform, SpO2 and PI are confirmed.
Preoxygenation will be standardized with the patient in a 20-30 degree head-up position, using a tight-fitting face mask without leak, FiO2 1.0 at a fresh gas flow of 10 L/min, and spontaneous tidal volume breathing for a maximum of 5 minutes. If a target is not reached within 5 minutes, the current values will be recorded and routine anesthesia care will proceed, with patient safety prioritized.
Measurements will be obtained at four time points: baseline before preoxygenation (T0), the moment ORI reaches 0.45 or higher (T1), the moment EtO2 reaches 90% or higher (T2), and the 3rd minute of preoxygenation (T3). At each time point, the time from T0, ORI, PI/PVI, SpO2, EtO2, EtCO2, heart rate and blood pressure will be recorded, and an arterial blood gas sample (PaO2, PaCO2, pH, SaO2, Hb) will be drawn from the existing arterial line. If time points coincide, a single sample will be used for all coinciding points to minimize blood sampling.
PaO2 values at T1, T2 and T3 will be compared within patients using repeated-measures ANOVA or the Friedman test, as appropriate, with Bonferroni-corrected pairwise comparisons. The time to reach each target and the proportion of patients reaching each target within 5 minutes will be described. Relationships between ORI, EtO2 and PaO2 will be examined using correlation methods that account for repeated measurements. The ability of ORI to discriminate PaO2 of 150 mmHg and 200 mmHg or higher will be explored with ROC analysis, and any derived cut-off values will be considered hypothesis-generating. The effects of age, BMI, sex, smoking history, hemoglobin, baseline oxygenation and PI/PVI will be explored descriptively. The results will be used to inform the sample size of a future confirmatory study.
- Conditions
- Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas
- Keywords
- Oxygen Reserve Index, ORI, Preoxygenation, End-Tidal Oxygen, EtO₂, PaO₂, Arterial Blood Gas, Pulse Co-Oximetry, Airway Managament, General Anesthesia, Perfusion Index
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
| Study group | Role | What they receive |
|---|---|---|
| Undergoing Elective Surgery With Preoxygenation | Adult patients (18-75 years, ASA I-III) scheduled for elective surgery under general anesthesia with endotracheal intubation, who have an arterial line placed for clinical reasons. All participants receive standardized preoxygenation with a tight-fitting face mask, FiO2 1.0 at a fresh gas flow of 10 L/min, in a 20-30 degree head-up position, with spontaneous tidal volume breathing for up to 5 minutes. ORI, EtO2 and SpO2 are monitored continuously. Arterial blood gas samples are taken from the existing arterial line at baseline, when ORI reaches 0.45, when EtO2 reaches 90%, and at the 3rd minute of preoxygenation. Each patient serves as their own control. |
What is being measured
The primary outcome is the main question the study is designed to answer.
Arterial Partial Pressure of Oxygen (PaO2) at Three Preoxygenation Targets
PaO2 (mmHg) measured by arterial blood gas analysis from the existing arterial line at three preoxygenation targets in the same patient: when the Oxygen Reserve Index (ORI) reaches 0.45 or higher (T1), when end-tidal oxygen (EtO2) reaches 90% or higher (T2), and at the 3rd minute of preoxygenation (T3). PaO2 values at these targets will be compared within patients. If time points coincide, a single sample will represent all coinciding targets.
Measured: During preoxygenation before induction of anesthesia (from baseline up to 5 minutes)
Secondary outcomes (4)
Time to Reach Each Preoxygenation Target
Time (seconds) from the start of preoxygenation (T0) to reach ORI of 0.45 or higher and EtO2 of 90% or higher.
Measured: During preoxygenation (up to 5 minutes)
Proportion of Patients Reaching Each Preoxygenation Target
Number and percentage of patients who reach ORI of 0.45 or higher and EtO2 of 90% or higher within 5 minutes of preoxygenation.
Measured: During preoxygenation (up to 5 minutes)
Correlation Between ORI, EtO2 and PaO2
Correlation coefficients between ORI and PaO2, EtO2 and PaO2, and ORI and EtO2, using all paired measurements at T0, T1, T2 and T3, accounting for repeated measurements within patients.
Measured: During preoxygenation (up to 5 minutes)
Diagnostic Performance of ORI for PaO2 of 150 mmHg and 200 mmHg or Higher
Area under the receiver operating characteristic curve (AUC) with 95% confidence interval for ORI in identifying PaO2 of 150 mmHg or higher and 200 mmHg or higher. Optimal cut-off values, sensitivity and specificity will be calculated using the Youden index, as exploratory analyses.
Measured: During preoxygenation (up to 5 minutes)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted6 Nov 2026
- Study start1 Dec 2026 (estimated)
- Primary completion1 May 2027 (estimated)
- Study completion1 Jun 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (13)Papers the sponsor has linked to this study.
- Other trials for Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood GasStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Cross-sectional
- Enrolment
- 30 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Kocaeli City Hospital
- Sponsor type
- Other government
- Responsible party
- Sponsor
- Investigators
- AYŞE ZEYNEP TURAN CIVRAZ, Associate Professor, Study director, KOCAELİ CITY HOSPİTAL
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07921849
- Sponsor's protocol ID
- KAEK//16.bI.03
- Status last verified
- Nov 2026
- First submitted
- 2 Nov 2026
- Last updated
- 6 Nov 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No: Individual participant data are not planned to be shared with external researchers because the approved protocol and informed consent process do not include external sharing of individual-level data. Study findings will be reported only in aggregate form in scientific presentations and publications to protect participant confidentiality.
Publications
Hirata N, Nishimura M, Chaki T, Yoshikawa Y, Yamakage M. Comparison between oxygen reserve index and end-tidal oxygen concentration for estimation of oxygenation during pre-oxygenation via a tight-fitted face mask: A prospective observational study. Eur J Anaesthesiol. 2021 Mar 1;38(3):313-315. doi: 10.1097/EJA.0000000000001358. No abstract available.
PubMed 33538433Abut YC, Kisa E. Comparison of the efficacy of two preoxygenation techniques using oxygen reserve index. Adv Clin Exp Med. 2025 Mar;34(3):337-342. doi: 10.17219/acem/188259.
PubMed 39248302Jung J, Chung YH, Koo BS, Kim SH, Jin HC, Chae WS. Efficiency of 80% vs. 100% Oxygen for Preoxygenation: A Randomized Study on Duration of Apnoea Without Desaturation. J Clin Med. 2025 Oct 28;14(21):7647. doi: 10.3390/jcm14217647.
PubMed 41227042Kocakulak D, Kucukosman G, Koksal BG, Baytar C, Okyay RD, Bollucuoglu K, Ozturk T, Piskin O, Ayoglu H. Investigation of preoxygenation methods in cesarean surgeries with the oxygen reserve index. Saudi Med J. 2022 Dec;43(12):1317-1323. doi: 10.15537/smj.2022.43.12.20220548.
PubMed 36517052Park S, Kim SY, Kim MS, Park WK, Byon HJ, Kim HJ. Comparison of preoxygenation efficiency measured by the oxygen reserve index between high-flow nasal oxygenation and facemask ventilation: a randomised controlled trial. BMC Anesthesiol. 2023 May 9;23(1):159. doi: 10.1186/s12871-023-02126-9.
PubMed 37161369Ishido H, Yoshida K, Isosu T, Obara S, Inoue S. Relationship between the updated oxygen reserve index and arterial partial pressure of oxygen: a prospective observational study. JA Clin Rep. 2025 Jun 16;11(1):34. doi: 10.1186/s40981-025-00796-7.
PubMed 40522542Yoshida K, Isosu T, Noji Y, Ebana H, Honda J, Sanbe N, Obara S, Murakawa M. Adjustment of oxygen reserve index (ORi) to avoid excessive hyperoxia during general anesthesia. J Clin Monit Comput. 2020 Jun;34(3):509-514. doi: 10.1007/s10877-019-00341-9. Epub 2019 Jun 22.
PubMed 31227971Massari D, de Keijzer IN, Vos JJ. Perioperative monitoring of the oxygen reserve: where do we stand? J Clin Monit Comput. 2023 Dec;37(6):1431-1433. doi: 10.1007/s10877-023-01085-3. Epub 2023 Oct 21.
PubMed 37863861Vos JJ, Willems CH, van Amsterdam K, van den Berg JP, Spanjersberg R, Struys MMRF, Scheeren TWL. Oxygen Reserve Index: Validation of a New Variable. Anesth Analg. 2019 Aug;129(2):409-415. doi: 10.1213/ANE.0000000000003706.
PubMed 30138170Jung J, Park S, Lee M, Chung YH, Koo BS, Kim SH, Chae WS. Efficacy of preoxygenation with end-tidal oxygen when using different oxygen concentrations in patients undergoing general surgery: a single-center retrospective observational study. Ann Palliat Med. 2022 Dec;11(12):3636-3647. doi: 10.21037/apm-22-647. Epub 2022 Dec 1.
PubMed 36510457Azam Danish M. Preoxygenation and Anesthesia: A Detailed Review. Cureus. 2021 Feb 9;13(2):e13240. doi: 10.7759/cureus.13240.
PubMed 33728189Ahmad I, El-Boghdadly K, Iliff H, Dua G, Higgs A, Huntington M, Mir F, Nouraei SAR, O'Sullivan EP, Patel A, Rivett K, McNarry AF. Difficult Airway Society 2025 guidelines for management of unanticipated difficult tracheal intubation in adults. Br J Anaesth. 2026 Jan;136(1):283-307. doi: 10.1016/j.bja.2025.10.006. Epub 2025 Nov 7.
PubMed 41203471Cook TM, Woodall N, Harper J, Benger J; Fourth National Audit Project. Major complications of airway management in the UK: results of the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society. Part 2: intensive care and emergency departments. Br J Anaesth. 2011 May;106(5):632-42. doi: 10.1093/bja/aer059. Epub 2011 Mar 29.
PubMed 21447489
Study at a glance
From the registry record, last updated by the sponsor on 6 Nov 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- "Comparison of Oxygen Reserve Index (ORI), End-Tidal Oxygen, and Time-Based Preoxygenation Targets With Arterial Blood Gas During Preoxygenation: A Prospective Cross-Over Study"
- ClinicalTrials.gov ID
- NCT07921849
- Acronym / sponsor ID
- KAEK//16.bI.03
- Conditions
- Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas
- Keywords
- Oxygen Reserve Index, ORI, Preoxygenation, End-Tidal Oxygen, EtO₂, PaO₂, Arterial Blood Gas, Pulse Co-Oximetry
- Study type
- Observational
- Recruitment status
- Not yet recruiting
- Enrolment
- 30 participants (estimated)
- Lead sponsor
- Kocaeli City HospitalOther government
- Study start
- 1 Dec 2026 (estimated)
- Primary completion
- 1 May 2027 (estimated)
- Study completion
- 1 Jun 2027 (estimated)
- First posted
- 6 Nov 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The goal of this observational study is to learn how well different preoxygenation targets reflect the actual amount of oxygen in the blood in adults having planned surgery under general anesthesia. Preoxygenation means breathing pure oxygen through a face mask before going to sleep, so that the body has an oxygen reserve while the breathing tube is placed.
Doctors usually decide that preoxygenation is adequate either after 3 minutes of breathing oxygen or when the oxygen level in exhaled air (end-tidal oxygen, EtO2) reaches 90% or more. A newer finger sensor measures the Oxygen Reserve Index (ORI), a noninvasive number that may show oxygen reserve continuously. However, it is not clear how closely these targets match the oxygen level measured directly in arterial blood (PaO2).
The main questions this study aims to answer are whether the arterial oxygen level (PaO2) differs when ORI reaches 0.45, when EtO2 reaches 90%, and at the 3rd minute of preoxygenation, and whether an ORI value of 0.45 or higher reflects an adequate arterial oxygen reserve.
Participants who already need an arterial line for their surgery will breathe 100% oxygen through a tight-fitting face mask for up to 5 minutes before anesthesia induction. Small blood samples will be taken from the existing arterial line at each target point. No additional invasive procedure will be done for the study.
Detailed description
Preoxygenation before induction of general anesthesia increases pulmonary oxygen stores by replacing nitrogen in the functional residual capacity with oxygen, thereby prolonging the safe apnea time during airway management. In clinical practice, preoxygenation adequacy is commonly judged by a fixed duration (3 minutes of tidal volume breathing) or by an end-tidal oxygen fraction (EtO2) of 90% or higher. Neither target directly or continuously reflects arterial oxygenation in every patient.
The Oxygen Reserve Index (ORI) is a relative, dimensionless index (0 to 1) derived from multi-wavelength pulse co-oximetry. It is intended to track changes in oxygen reserve noninvasively in the mild-to-moderate hyperoxic range, where SpO2 plateaus. ORI thresholds depend on the device algorithm and sensor generation; with the updated algorithm, an ORI cut-off of 0.45 has been reported for PaO2 of 150 mmHg or higher. Prospective data that compare ORI, EtO2 and time-based preoxygenation targets against simultaneous arterial blood gas measurements in the same patient are limited.
This is a prospective, single-center, observational study with a repeated-measures design, in which each patient serves as their own control. It is planned as a pilot study of 30 patients. Adult patients (18-75 years, ASA I-III) scheduled for elective surgery under general anesthesia with endotracheal intubation, who require invasive arterial cannulation for clinical reasons, will be enrolled after written informed consent. Arterial cannulation will not be performed for research purposes.
Standard monitoring will include ECG, noninvasive and invasive arterial blood pressure, heart rate, SpO2, EtO2/EtCO2 (anesthesia machine gas analyzer), and ORI (Masimo multi-wavelength pulse co-oximetry), with perfusion index (PI) and pleth variability index (PVI) when available. The ORI sensor will be placed on the same finger (left fourth finger) throughout the measurements. Factors affecting the optical signal, such as nail polish, ambient light, motion and improper placement, will be controlled. ORI values will be recorded only after a stable plethysmographic waveform, SpO2 and PI are confirmed.
Preoxygenation will be standardized with the patient in a 20-30 degree head-up position, using a tight-fitting face mask without leak, FiO2 1.0 at a fresh gas flow of 10 L/min, and spontaneous tidal volume breathing for a maximum of 5 minutes. If a target is not reached within 5 minutes, the current values will be recorded and routine anesthesia care will proceed, with patient safety prioritized.
Measurements will be obtained at four time points: baseline before preoxygenation (T0), the moment ORI reaches 0.45 or higher (T1), the moment EtO2 reaches 90% or higher (T2), and the 3rd minute of preoxygenation (T3). At each time point, the time from T0, ORI, PI/PVI, SpO2, EtO2, EtCO2, heart rate and blood pressure will be recorded, and an arterial blood gas sample (PaO2, PaCO2, pH, SaO2, Hb) will be drawn from the existing arterial line. If time points coincide, a single sample will be used for all coinciding points to minimize blood sampling.
PaO2 values at T1, T2 and T3 will be compared within patients using repeated-measures ANOVA or the Friedman test, as appropriate, with Bonferroni-corrected pairwise comparisons. The time to reach each target and the proportion of patients reaching each target within 5 minutes will be described. Relationships between ORI, EtO2 and PaO2 will be examined using correlation methods that account for repeated measurements. The ability of ORI to discriminate PaO2 of 150 mmHg and 200 mmHg or higher will be explored with ROC analysis, and any derived cut-off values will be considered hypothesis-generating. The effects of age, BMI, sex, smoking history, hemoglobin, baseline oxygenation and PI/PVI will be explored descriptively. The results will be used to inform the sample size of a future confirmatory study.
Study design
- Observational model
- Cohort
- Time perspective
- Cross-sectional
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Undergoing Elective Surgery With Preoxygenation | – | –Adult patients (18-75 years, ASA I-III) scheduled for elective surgery under general anesthesia with endotracheal intubation, who have an arterial line placed for clinical reasons. All participants receive standardized preoxygenation with a tight-fitting face mask, FiO2 1.0 at a fresh gas flow of 10 L/min, in a 20-30 degree head-up position, with spontaneous tidal volume breathing for up to 5 minutes. ORI, EtO2 and SpO2 are monitored continuously. Arterial blood gas samples are taken from the existing arterial line at baseline, when ORI reaches 0.45, when EtO2 reaches 90%, and at the 3rd minute of preoxygenation. Each patient serves as their own control. |
Who may qualify
- Ages
- 18 to 75 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
- Study population
- The study population will consist of adult patients undergoing elective surgery of any surgical specialty under general anesthesia with endotracheal intubation at the Department of Anesthesiology and Reanimation, Kocaeli City Hospital, Izmit, Turkey. Only patients in whom invasive arterial cannulation is clinically indicated as part of their routine anesthetic management will be approached, for example because of the type and expected duration of surgery, anticipated blood loss or hemodynamic changes, the need for repeated blood gas analysis, or patient comorbidities. Arterial cannulation will not be performed for research purposes. Eligible patients will be identified during the preoperative anesthesia assessment and enrolled consecutively after written informed consent is obtained.
Key inclusion criteria (7 listed)
- Age 18-75 years
- ASA physical status I-III
- Scheduled for elective surgery
- Planned general anesthesia with endotracheal intubation
- Invasive arterial cannulation planned for clinical reasons
Key exclusion criteria (11 listed)
- Emergency surgery
- SpO2 below 94% on room air
- Advanced chronic obstructive pulmonary disease (COPD) or severe restrictive lung disease
- Hemodynamic instability
- Severe peripheral circulatory disorder
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Primary outcome
Arterial Partial Pressure of Oxygen (PaO2) at Three Preoxygenation Targets
Time frame: During preoxygenation before induction of anesthesia (from baseline up to 5 minutes)
PaO2 (mmHg) measured by arterial blood gas analysis from the existing arterial line at three preoxygenation targets in the same patient: when the Oxygen Reserve Index (ORI) reaches 0.45 or higher (T1), when end-tidal oxygen (EtO2) reaches 90% or higher (T2), and at the 3rd minute of preoxygenation (T3). PaO2 values at these targets will be compared within patients. If time points coincide, a single sample will represent all coinciding targets.
4 secondary outcomes
Time to Reach Each Preoxygenation Target
Time frame: During preoxygenation (up to 5 minutes)
Proportion of Patients Reaching Each Preoxygenation Target
Time frame: During preoxygenation (up to 5 minutes)
Correlation Between ORI, EtO2 and PaO2
Time frame: During preoxygenation (up to 5 minutes)
Diagnostic Performance of ORI for PaO2 of 150 mmHg and 200 mmHg or Higher
Time frame: During preoxygenation (up to 5 minutes)
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 6 Nov 2026.
- Background: PubMed 33538433Hirata N, Nishimura M, Chaki T, Yoshikawa Y, Yamakage M. Comparison between oxygen reserve index and end-tidal oxygen concentration for estimation of oxygenation during pre-oxygenation via a tight-fitted face mask: A prospective observational study. Eur J Anaesthesiol. 2021 Mar 1;38(3):313-315. doi: 10.1097/EJA.0000000000001358. No abstract available.
- Background: PubMed 39248302Abut YC, Kisa E. Comparison of the efficacy of two preoxygenation techniques using oxygen reserve index. Adv Clin Exp Med. 2025 Mar;34(3):337-342. doi: 10.17219/acem/188259.
- Background: PubMed 41227042Jung J, Chung YH, Koo BS, Kim SH, Jin HC, Chae WS. Efficiency of 80% vs. 100% Oxygen for Preoxygenation: A Randomized Study on Duration of Apnoea Without Desaturation. J Clin Med. 2025 Oct 28;14(21):7647. doi: 10.3390/jcm14217647.
- Background: PubMed 36517052Kocakulak D, Kucukosman G, Koksal BG, Baytar C, Okyay RD, Bollucuoglu K, Ozturk T, Piskin O, Ayoglu H. Investigation of preoxygenation methods in cesarean surgeries with the oxygen reserve index. Saudi Med J. 2022 Dec;43(12):1317-1323. doi: 10.15537/smj.2022.43.12.20220548.
- Background: PubMed 37161369Park S, Kim SY, Kim MS, Park WK, Byon HJ, Kim HJ. Comparison of preoxygenation efficiency measured by the oxygen reserve index between high-flow nasal oxygenation and facemask ventilation: a randomised controlled trial. BMC Anesthesiol. 2023 May 9;23(1):159. doi: 10.1186/s12871-023-02126-9.
- Background: PubMed 40522542Ishido H, Yoshida K, Isosu T, Obara S, Inoue S. Relationship between the updated oxygen reserve index and arterial partial pressure of oxygen: a prospective observational study. JA Clin Rep. 2025 Jun 16;11(1):34. doi: 10.1186/s40981-025-00796-7.
- Background: PubMed 31227971Yoshida K, Isosu T, Noji Y, Ebana H, Honda J, Sanbe N, Obara S, Murakawa M. Adjustment of oxygen reserve index (ORi) to avoid excessive hyperoxia during general anesthesia. J Clin Monit Comput. 2020 Jun;34(3):509-514. doi: 10.1007/s10877-019-00341-9. Epub 2019 Jun 22.
- Background: PubMed 37863861Massari D, de Keijzer IN, Vos JJ. Perioperative monitoring of the oxygen reserve: where do we stand? J Clin Monit Comput. 2023 Dec;37(6):1431-1433. doi: 10.1007/s10877-023-01085-3. Epub 2023 Oct 21.
- Background: PubMed 30138170Vos JJ, Willems CH, van Amsterdam K, van den Berg JP, Spanjersberg R, Struys MMRF, Scheeren TWL. Oxygen Reserve Index: Validation of a New Variable. Anesth Analg. 2019 Aug;129(2):409-415. doi: 10.1213/ANE.0000000000003706.
- Background: PubMed 36510457Jung J, Park S, Lee M, Chung YH, Koo BS, Kim SH, Chae WS. Efficacy of preoxygenation with end-tidal oxygen when using different oxygen concentrations in patients undergoing general surgery: a single-center retrospective observational study. Ann Palliat Med. 2022 Dec;11(12):3636-3647. doi: 10.21037/apm-22-647. Epub 2022 Dec 1.
- Background: PubMed 33728189Azam Danish M. Preoxygenation and Anesthesia: A Detailed Review. Cureus. 2021 Feb 9;13(2):e13240. doi: 10.7759/cureus.13240.
- Background: PubMed 41203471Ahmad I, El-Boghdadly K, Iliff H, Dua G, Higgs A, Huntington M, Mir F, Nouraei SAR, O'Sullivan EP, Patel A, Rivett K, McNarry AF. Difficult Airway Society 2025 guidelines for management of unanticipated difficult tracheal intubation in adults. Br J Anaesth. 2026 Jan;136(1):283-307. doi: 10.1016/j.bja.2025.10.006. Epub 2025 Nov 7.
- Individual participant dataSharing planned: No. Individual participant data are not planned to be shared with external researchers because the approved protocol and informed consent process do not include external sharing of individual-level data. Study findings will be reported only in aggregate form in scientific presentations and publications to protect participant confidentiality.
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
AYŞE ZEYNEP TURAN CIVRAZ, Associate Professor study director
KOCAELİ CITY HOSPİTAL
Questions about this trial
What is this clinical trial studying?
An observational study of Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas, run by Kocaeli City Hospital.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 11 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: opening soon, as of the sponsor's last update on 6 Nov 2026. Status can change between updates, so confirm with the study contact before making plans.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact AYŞE ZEYNEP TURAN CIVRAZ, Associate Professor (+90 505 469 58 50, ayse.zeynep@gmail.com), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Arterial Partial Pressure of Oxygen (PaO2) at Three Preoxygenation Targets (time frame: During preoxygenation before induction of anesthesia (from baseline up to 5 minutes)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07921849, which also lists 13 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 6 Nov 2026.