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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.
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.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Oxygen Reserve Index | Experimental | 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. |
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| Peripheral oxygen saturation | No Intervention | 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. |
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| oxygen monitoring techniques | Procedure | 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. |
| Measure | Description | Time Frame |
|---|---|---|
| Time to Reventilation Threshold | 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). |
| Measure | Description | Time Frame |
|---|---|---|
| Arterial Blood Gas Parameters at Reventilation | 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). |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Demet Altun, Prof | Contact | 00905326811767 | drdemetaltun@hotmail.com | |
| ece naz demir, resident | Contact | 00905064524892 | ecenazdemir95@gmail.com |
| Name | Affiliation | Role |
|---|---|---|
| ece naz demir, resident | Istanbul University | Principal Investigator |
| demet altun, prof | Istanbul University | Study Director |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Istanbul University, Department of anesthesiology | Istanbul | Fatih | 34093 | Turkey (Türkiye) |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 32815872 | Result | Fleming NW, Singh A, Lee L, Applegate RL 2nd. Oxygen Reserve Index: Utility as an Early Warning for Desaturation in High-Risk Surgical Patients. Anesth Analg. 2021 Mar 1;132(3):770-776. doi: 10.1213/ANE.0000000000005109. | |
| 26978143 | Result | Szmuk P, Steiner JW, Olomu PN, Ploski RP, Sessler DI, Ezri T. Oxygen Reserve Index: A Novel Noninvasive Measure of Oxygen Reserve--A Pilot Study. Anesthesiology. 2016 Apr;124(4):779-84. doi: 10.1097/ALN.0000000000001009. |
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Model Description
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Masking Description
| Perioperative Lung Ultrasound Findings |
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 | 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 | First recorded EtCO₂ value during apnea prior to reventilation. | During the apneic period, measured at the time of reventilation during surgery. |