An observational study in Preoxygenation Adequacy Assessed by Oxygen Reserve Index, End-tidal Oxygen and Arterial Blood Gas, sponsored by Kocaeli City Hospital. Not yet recruiting. Open to participants aged 18 Years to 75 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-06.
Sponsored by Kocaeli City Hospital · Observational
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.
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.
Kocaeli City Hospital is the lead sponsor of 44 studies on the registry; 19 are open to participants now.
Counted across the registry records on this site, refreshed daily.
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.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
The anaesthetists’ scale of health before surgery: I is healthy, II has a mild illness that is under control, III a severe one, IV a severe illness that is a constant threat to life. V and VI are used for the critically ill and for organ donors.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Chronic obstructive pulmonary disease: long-term lung disease that makes it hard to breathe out, including emphysema and chronic bronchitis.
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
ASA physical status
The anaesthetists’ scale of health before surgery: I is healthy, II has a mild illness that is under control, III a severe one, IV a severe illness that is a constant threat to life. V and VI are used for the critically ill and for organ donors.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
COPD
Chronic obstructive pulmonary disease: long-term lung disease that makes it hard to breathe out, including emphysema and chronic bronchitis.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hemoglobin (Hb)
The protein in red blood cells that carries oxygen. A low level is anaemia, which can cause tiredness and breathlessness. Measured in g/dL or g/L (9 g/dL is 90 g/L).
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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.
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.
Time frame: During preoxygenation before induction of anesthesia (from baseline up to 5 minutes)
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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: During preoxygenation (up to 5 minutes)
No study locations are listed for this record.
Plan to share: 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.
Start is estimated for Dec 2026; primary completion for May 2027, 5 months later.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is not yet recruiting, as verified in Nov 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Kocaeli City Hospital