Assessing the incidence of hyperoxia and the effectiveness of Oxygen Reserve Index-guided FiO2 titration in hyperoxia prevention

BACKGROUND

Although pulse oximetry technology, which is considered the standard of care to ensure optimum oxygenation, is indispensable in clinical practice, especially in the detection of hypoxemia, it has some limitations in the detection of hyperoxemia. Oxygen Reserve Index can provide clinicians with a crucial pathway in detecting and preventing hyperoxia, noninvasively. Our aim in this study is to determine the hyperoxia detection ability of ORi and to investigate the effectiveness of ORi and SpO2-guided FiO2 titration in preventing hyperoxia.

METHODS

This prospective randomized study was conducted in the operating theater of Health Sciences University İzmir Tepecik Training and Research Hospital from September 1, 2020, to December 1, 2022. Patients undergoing major abdominal surgery were divided into two groups: the control group and the SpO2 + ORi group. FiO2 titration was performed in the SpO2 + ORi group to maintain the ORi between 0.00 and 95% < SpO2 ≤ 98%. Parameters were recorded before induction, 10 min after intubation, and every hour during the operation.

RESULTS

A positive linear relationship of 75.8% (r = 0.758) was found between PaO2 and ORi in the ORi + SpO2 group (p < 0.001). Moderate hyperoxemia was observed in 31.6% of patients in the control group, while it was not observed in the ORi + SpO2 group at the 3rd hour. PaO2 values decreased significantly over time in the ORi + SpO2 group with FiO2 titration (p < 0.001).

CONCLUSION

The combined use of SpO2 and ORi has been demonstrated to successfully guide FiO2 titration for optimal oxygenation and reduce hyperoxemia.

Oxygen reserve index versus conventional peripheral oxygen saturation for prevention of hypoxaemia: A randomised controlled trial

BACKGROUND

Hypoxaemia occurs frequently during paediatric laryngeal microsurgery.

OBJECTIVE

The oxygen reserve index is a noninvasive and continuous parameter to assess PaO2 levels in the range of 100 to 200 mmHg. It ranges from 0 to 1.0. We investigated whether monitoring the oxygen reserve index can reduce the incidence of SpO2 90% or less.

DESIGN

Randomised controlled trial.

SETTING

A tertiary care paediatric hospital.

PARTICIPANTS

Paediatric patients aged 18 years or less scheduled to undergo laryngeal microsurgery.

INTERVENTION

The patients were randomly allocated to the oxygen reserve index or control groups, and stratified based on the presence of a tracheostomy tube. Rescue intervention was performed when the oxygen reserve index was 0.2 or less and the SpO2 was 94% or less in the oxygen reserve index and control groups, respectively.

MAIN OUTCOME MEASURE

The primary outcome was the incidence of SpO2 90% or less during the surgery.

RESULTS

Data from 88 patients were analysed. The incidence of SpO2 ≤ 90% did not differ between the oxygen reserve index and control groups [P = 0.114; 11/44, 25% vs. 18/44, 40.9%; relative risk: 1.27; and 95% confidence interval (CI): 0.94 to 1.72]. Among the 128 rescue interventions, SpO2 ≤ 90% event developed in 18 out of 75 events (24%) and 42 out of 53 events (79.2%) in the oxygen reserve index and control groups, respectively (P < 0.001; difference: 55.2%; and 95% CI 38.5 to 67.2%). The number of SpO2 ≤ 90% events per patient in the oxygen reserve index group (median 0, maximum 3) was less than that in the control group (median 0, maximum 8, P = 0.031).

CONCLUSION

Additional monitoring of the oxygen reserve index, with a target value of greater than 0.2 during paediatric airway surgery, alongside peripheral oxygen saturation, did not reduce the incidence of SpO2 ≤ 90%.

Oxygen concentration titration guided by oxygen reserve index during pediatric laryngeal surgery with high-flow nasal cannula oxygen: a randomized controlled trial

PURPOSE

The objective of this study was to evaluate whether adjusting the oxygen concentration guided by the Oxygen Reserve Index (ORI) during pediatric laryngeal surgery with High Flow Nasal Cannula Oxygen (HFNO) could achieve postoperative PaO2 close to physiological levels while ensuring adequate oxygenation in surgery.

METHODS

Sixty pediatric patients undergoing laryngeal surgery or examination were randomly assigned to two groups. The ORI group received oxygen concentration adjustments every 5 min to maintain a target ORI value of 0.21, whereas the control group did not undergo any adjustments. Postoperative PaO2, time weighted average fraction of inspired oxygen (FiO2), and mean Peripheral Oxygen Saturation (SpO2) were compared between groups. Finally, some analyses were conducted to examine the relationship of ORI with PaO2.

RESULTS

In general, the postoperative PaO2 was 164.9 ± 48.8 mmHg in ORI group and 323.0 ± 87.7 mmHg in control group (P < 0.01). The time weighted average FiO2 in the ORI group was 85.9 [81.8-92.7] %. There was no significant difference in mean SpO2 between the two groups (ORI vs. control: 98.4 [97.7-99.2] vs. 98.8 [97.7-99.5]; P = 0.36). According to the analyses, the optimal cut value for ORI was determined to be 0.195 when PaO2 was 150 mmHg.

CONCLUSIONS

In pediatric laryngeal surgery with HFNO, reducing oxygen concentration guided by ORI helped achieve postoperative PaO2 levels closer to physiological norms without compromising intra-operative oxygenation.

What are standard monitoring devices for anesthesia in future?

Monitoring the patient's physiological functions is critical in clinical anesthesia. The latest version of the Japanese Society of Anesthesiologists' Guidelines for Safe Anesthesia Monitoring, revised in 2019, covers various factors, including electroencephalogram monitoring, oxygenation, ventilation, circulation, and muscle relaxation. However, with recent advances in monitoring technologies, the information provided has become more detailed, requiring practitioners to update their knowledge. At a symposium organized by the Journal of Anesthesia in 2023, experts across five fields discussed their respective topics: anesthesiologists need to interpret not only the values displayed on processed electroencephalogram monitors but also raw electroencephalogram data in the foreseeable future. In addition to the traditional concern of preventing hypoxemia, monitoring for potential hyperoxemia and the effects of mechanical ventilation itself will become increasingly important. The importance of using AI analytics to predict hypotension, assess nociception, and evaluate microcirculation may increase. With the recent increase in the availability of neuromuscular monitoring devices in Japan, it is important for anesthesiologists to become thoroughly familiar with the features of each device to ensure its effective use. There is a growing desire to develop and introduce a well-organized, integrated "single screen" monitor.

Evaluation of the relationship between the STOP-Bang score with oxygen reserve index and difficult airway: a prospective observational study

BACKGROUND

Patients diagnosed with Obstructive Sleep Apnea (OSA) syndrome have a tendency towards hypoventilation, hypoxia, and hypercarbia in the perioperative period. This study hypothesized that the Oxygen Reserve Index (ORi) could predict possible hypoxia and determine difficult airways in patients at risk for OSA, as determined by the STOP-Bang questionnaire.

METHODS

This prospective study included adult patients undergoing elective surgery under general anesthesia with endotracheal intubation, divided into two groups: low risk (0-2 points) and high risk (3-8 points) based on their STOP-Bang questionnaire results. The primary outcome measure was the highest ORi value reached during preoxygenation and the time to reach this value. Data were recorded at four time points: before preoxygenation (T1), end of preoxygenation (T2), end of mask ventilation (T3), and end of intubation (T4), as well as partial oxygen pressure values in T1, T2, and T4. The secondary outcome measures were the grading scale for mask ventilation, Cormack-Lehane score, tonsil dimensions, use of a stylet, and application of the burp maneuver during intubation.

RESULTS

In the high-risk group, preoperative peripheral oxygen saturation values, the highest ORi value reached in preoxygenation, and ORi values at T3 and T4 times were lower, and the time to reach the highest ORi value was longer (p < 0.05).

CONCLUSION

Using ORi in patients with OSA may be useful in evaluating oxygenation, and since difficult airway is more common, ORi monitoring will better manage possible hypoxic conditions.

Association between Oxygen Reserve index and arterial partial pressure of oxygen during one-lung ventilation: a retrospective cohort study

PURPOSE

We aimed to investigate the association between the Oxygen Reserve index (ORi) and arterial partial pressure of oxygen (PaO2) during one-lung ventilation in patients who underwent non-cardiac thoracic surgery requiring one-lung ventilation.

METHODS

This retrospective study assessed the eligibility of 578 adult patients who underwent elective non-cardiac thoracic surgery requiring one-lung ventilation at a tertiary hospital, and their electronic medical records were reviewed. The ORi monitor was used in all patients during anesthesia, and arterial blood gas analysis was routinely performed 15 min after the initiation of one-lung ventilation. The primary endpoint was the association between ORi and PaO2 which were measured simultaneously during one-lung ventilation. We also investigated the risk factors for PaO2 less than 150 mmHg during one-lung ventilation.

RESULTS

Total of 554 patient were included in the analysis. The ORi value measured 15 min after the start of one-lung ventilation was significantly associated with PaO2 in the linear regression model (r2 = 0.5752, P < 0.001), and 0.27 of the ORi value could distinguish PaO2 ≥ 150 mmHg (sensitivity 0.909, specificity 0.932). Risk factors for PaO2 < 150 mmHg during one-lung ventilation included a lower ORi, older age, higher body mass index, left-sided one-lung ventilation, and lower hemoglobin concentrations.

CONCLUSION

This study suggested that ORi could provide useful information on arterial oxygenation even during one-lung ventilation for non-cardiac thoracic surgery.

Early warning for SpO2 decrease by the oxygen reserve index in neonates and small infants

INTRODUCTION

Continuously assessing the oxygenation levels of patients to detect and prevent hypoxemia can be advantageous for safe anesthesia, especially in neonates and small infants. The oxygen reserve index (ORI) is a new parameter that can assess oxygenation through a relationship with arterial oxygen partial pressure (PaO2 ). The aim of this study was to examine whether the ORI provides a clinically relevant warning time for an impending SpO2 (pulse oximetry hemoglobin saturation) reduction in neonates and small infants.

METHODS

ORI and SpO2 were measured continuously in infants aged <2 years during general anesthesia. The warning time and sensitivity of different ORI alarms for detecting impending SpO2 decrease were calculated. Subsequently, the agreement of the ORI and PaO2 with blood gas analyses was assessed.

RESULTS

The ORI of 100 small infants and neonates with a median age of 9 months (min-max, 0-21 months) and weight of 8.35 kg (min-max, 2-13 kg) were measured. For the ORI/PaO2 correlation, 54 blood gas analyses were performed. The warning time and sensitivity of the preset ORI alarm during the entire duration of anesthesia were 84 s (25th-75th percentile, 56-102 s) and 55% (95% CI 52%-58%), and those during anesthesia induction were 63 s (40-82 s) and 56% (44%-68%), respectively. The positive predictive value of the preset ORI alarm were 18% (95% CI 17%-20%; entire duration of anesthesia) and 27% (95% CI 21%-35%; during anesthesia induction). The agreement of PaO2 intervals with the ORI intervals was poor, with a kappa of 0.00 (95% CI = [-0.18; 0.18]). The weight (p = .0129) and height (p = .0376) of the infants and neonates were correlated to the correct classification of the PaO2 interval with the ORI interval.

CONCLUSIONS

The ORI provided an early warning time for detecting an impending SpO2 decrease in small infants and neonates in the defined interval in this study. However, the sensitivity of ORI to forewarn a SpO2 decrease and the agreement of the ORI with PaO2 intervals in this real-life scenario were too poor to recommend the ORI as a useful early warning indicator for this age group.

Oxygen reserve index guided fraction of inspired oxygen titration to reduce hyperoxemia during laparoscopic gastrectomy: A randomized controlled trial

BACKGROUND

The usefulness of the oxygen reserve index (ORi) in reducing hyperoxemia remains unclear. We designed this study to investigate whether fraction of inspired oxygen (FiO2) adjustment under a combination of ORi and peripheral oxygen saturation (SpO2) guidance can reduce intraoperative hyperoxemia compared to SpO2 alone.

METHODS

In this prospective, double-blind, randomized controlled study, we allocated patients scheduled for laparoscopic gastrectomy to the SpO2 group (FiO2 adjusted to target SpO2 ≥ 98%) or the ORi-SpO2 group (FiO2 adjusted to target 0 < 0 ORi < .3 and SpO2 ≥ 98%). The ORi, SpO2, FiO2, arterial partial pressure of oxygen (PaO2), and incidence of severe hyperoxemia (PaO2 ≥ 200 mm Hg) were recorded before and 1, 2, and 3 hours after surgical incision. Data from 32 and 30 subjects in the SpO2 and ORi-SpO2 groups, respectively, were analyzed.

RESULTS

PaO2 was higher in the SpO2 group (250.31 ± 57.39 mm Hg) than in the ORi-SpO2 group (170.07 ± 49.39 mm Hg) 1 hour after incision (P < .001). PaO2 was consistently higher in the SpO2 group than in the ORi-SpO2 group, over time (P = .045). The incidence of severe hyperoxemia was higher in the SpO2 group (84.4%) than in the ORi-SpO2 group (16.7%, P < .001) 1 hour after incision. Higher FiO2 was administered to the SpO2 group [52.5 (50-60)] than the ORi-SpO2 group [40 (35-50), P < .001] 1 hour after incision. SpO2 was not different between the 2 groups.

CONCLUSION

The combination of ORi and SpO2 guided FiO2 adjustment reduced hyperoxemia compared to SpO2 alone during laparoscopic gastrectomy.

[Oxygen reserve index: a new parameter for oxygen therapy]

Oxygen reserve index (ORI) is a novel dimensionless index used for noninvasive, real-time, and continuous monitoring of oxygenation, and ORI value ranges from 0 to 1, which reflects the range of 100-200 mmHg for arterial partial pressure of oxygen. ORI combined with pulse oximetry may help to accurately adjust the concentration of inspired oxygen and prevent hyperoxemia and hypoxemia. ORI is suitable for various clinical situations, and the medical staff should master this novel parameter and use it properly to assess the oxygenation of patients. In addition, several limitations of ORI should be noticed during clinical application.

Anesthetic management in a patient with severe tracheal stenosis by monitoring oxygen reserve index

Background

General anesthesia for tracheal stenting is challenging because of difficult ventilation and accompanying hypoxia. We report the use of oxygen reserve index (ORi™) during tracheal stenting.

Case presentation

Cauterization of an intratracheal tumor and tracheal stenting was scheduled in a patient. ORi decreased from 0.3 to 0.2 after starting cauterization using a flexible bronchoscope through a tracheal tube with 28% oxygen, while SpO₂ was maintained at 100%. ORi further decreased to 0, followed by a decrease of SpO₂ < 90%, and surgery was interrupted. SpO₂ was increased shortly after increasing FiO₂ to 1.0, but ORi remained 0 when surgery was resumed; it was increased after completion of cauterization. Both ORi and SpO₂ were maintained above 0.4 and 98%, respectively, during tracheal stenting through a rigid bronchoscope under intrapulmonary percussive ventilation.

Conclusion

ORi was useful for predicting a decrease of SpO₂ under general anesthesia for tracheal stenting.

Continuous Titration of Inspired Oxygen Using Oxygen Reserve Index to Decrease Oxygen Exposure During One-Lung Ventilation: A Randomized Controlled Trial

BACKGROUND

A high fraction of inspired oxygen (Fio2) is administered during one-lung ventilation (OLV). However, a high Fio2 is not physiologic and may lead to various complications. We hypothesized that continuous titration of Fio2 using the oxygen reserve index (ORI) reduces oxygen exposure compared to conventional management during OLV.

METHODS

In this randomized, double-blinded trial, patients undergoing thoracic surgery were assigned to an ORI (n = 64) or a control group (n = 60). In the ORI group, ORI was continuously displayed using multiwavelength pulse co-oximetry (Masimo) between 0 and 1 (0, no reserve; 1, maximum reserve), and Fio2 was titrated for a target ORI of 0.21 at 5-minute intervals during OLV. In the control group, Fio2 was adjusted using arterial blood gas analysis measured at 15 minutes after OLV initiation. The primary end point was the time-weighted average Fio2 during OLV.

RESULTS

Overall, time-weighted average Fio2 did not differ between the groups (control versus ORI: median [interquartile range], 0.87 [0.73-1.00] vs 0.82 [0.68-0.93]; P = .09). However, in a subgroup analysis, the ORI group reduced time-weighted average Fio2 after pulmonary vascular ligation compared to the control group (control versus ORI: median [interquartile range], 0.75 [0.70-1.00] vs 0.72 [0.59-0.89]; P = .0261). The incidence of intraoperative hypoxia (arterial oxygen saturation [Spo2] <94%; control versus ORI: 32% [19/60; 95% confidence interval (CI), 20-45] vs 19% [12/64; 95% CI, 10-31]; P = .09), and postoperative complications within the first 7 days did not differ between the groups.

CONCLUSIONS

ORI-guided continuous Fio2 titration does not reduce overall oxygen exposure during OLV.

The ability of Oxygen Reserve Index® to detect hyperoxia in critically ill patients

Background

Hyperoxia is associated with increased morbidity and mortality in the intensive care unit. Classical noninvasive measurements of oxygen saturation with pulse oximeters are unable to detect hyperoxia. The Oxygen Reserve Index (ORI) is a continuous noninvasive parameter provided by a multi-wave pulse oximeter that can detect hyperoxia. Primary objective was to evaluate the diagnostic accuracy of the ORI for detecting arterial oxygen tension (PaO₂) > 100 mmHg in neurocritical care patients. Secondary objectives were to test the ability of ORI to detect PaO₂ > 120 mmHg and the ability of pulse oximetry (SpO₂) to detect PaO₂ > 100 mmHg and PaO₂ > 120 mmHg.

Methods

In this single-center study, we collected ORI and arterial blood samples every 6 h for 3 consecutive days. Diagnostic performance was estimated using the area under the receiver operating characteristic curve (AUROC).

Results

There were 696 simultaneous measurements of ORI and PaO₂ in 62 patients. Considering the repeated measurements, the correlation between ORI and PaO₂ was r = 0.13. The area under the receiver operating characteristic curve (AUROC), obtained to test the ability of ORI to detect PaO₂ > 100 mmHg, was 0.567 (95% confidence interval = 0.566–0.569) with a sensitivity of 0.233 (95%CI = 0.230–0.235) and a specificity of 0.909 (95%CI = 0.907–0.910). The AUROC value obtained to test the ability of SpO₂ to detect a PaO₂ > 100 mmHg was 0.771 (95%CI = 0.770–0.773) with a sensitivity of 0.715 (95%CI = 0.712–0.718) and a specificity of 0.700 (95%CI = 0.697–0.703). The diagnostic performance of ORI and SpO₂ for detecting PaO₂ > 120 mmHg was AUROC = 0.584 (95%CI = 0.582–0.586) and 0.764 (95%CI = 0.762–0.766), respectively. The AUROC obtained for SpO₂ was significantly higher than that for ORI (p < 0.01). Diagnostic performance was not affected by sedation, norepinephrine infusion, arterial partial pressure of carbon dioxide, hemoglobin level and perfusion index.

Conclusion

In a specific population of brain-injured patients hospitalized in a neurointensive care unit, our results suggest that the ability of ORI to diagnose hyperoxia is relatively low and that SpO₂ provides better detection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01012-w.

How early warning with the Oxygen Reserve Index (ORi™) can improve the detection of desaturation during induction of general anesthesia?

The Oxygen Reserve Index (ORi™) is a dimensionless parameter with a value between 0 and 1. It is related to the real-time oxygenation status in the moderate hyperoxic range. The purpose of this study is to investigate the added warning time provided by different ORi alarm triggers and the continuous trends of ORi, SpO₂, and PaO₂. We enrolled 25 patients who were scheduled for elective surgery under general anesthesia with planned arterial catheterization before induction. The participants received standardized preoxygenation, induction, and intubation. The patients remained apneic and ventilation was resumed when the SpO₂ fell below 90%. The ORi and SpO₂ were recorded every ten seconds and arterial blood was sampled every minute, from preoxygenation to resumed ventilation. Alarm triggers set to the ORi peak and the ORi 0.55 values provided 300 and 145 s of significant added warning time compared to SpO₂ (p < 0.0001). The coefficient of determination was 0.56 between the ORi and the PaO₂ ≤ 240 mmHg and showed a positive correlation. The ORi enables the clinicians to monitor the patients' oxygen status during induction of general anesthesia and can improve the detection of impending desaturation. However, further studies are needed to assess its clinical potential in the high hyperoxic range.The protocol was retrospectively registered at ClinicalTrials.gov on July 21, 2021 (NCT04976504).

The use of oxygen reserve index in one-lung ventilation and its impact on peripheral oxygen saturation, perfusion index and, pleth variability index

Background

Our goal is to investigate the use of the oxygen reserve index (ORi) to detect hypoxemia and its relation with parameters such as; peripheral oxygen saturation, perfusion index (PI), and pleth variability index (PVI) during one-lung ventilation (OLV).

Methods

Fifty patients undergoing general anesthesia and OLV for elective thoracic surgeries were enrolled in an observational cohort study in a tertiary care teaching hospital. All patients required OLV after a left-sided double-lumen tube insertion during intubation. The definition of hypoxemia during OLV is a peripheral oxygen saturation (SpO2) value of less than 95%, while the inspired oxygen fraction (FiO2) is higher than 50% on a pulse oximetry device. ORi, pulse oximetry, PI, and PVI values were measured continuously. Sensitivity, specificity, positive and negative predictive values, likelihood ratios, and accuracy were calculated for ORi values equal to zero in different time points during surgery to predict hypoxemia. At Clinicaltrials.gov registry, the Registration ID is NCT05050552.

Results

Hypoxemia was observed in 19 patients (38%). The accuracy for predicting hypoxemia during anesthesia induction at ORi value equals zero at 5 min after intubation in the supine position (DS5) showed a sensitivity of 92.3% (95% CI 84.9–99.6), specificity of 81.1% (95% CI 70.2–91.9), and an accuracy of 84.0% (95% CI 73.8–94.2). For predicting hypoxemia, ORi equals zero show good sensitivity, specificity, and statistical accuracy values for time points of DS5 until OLV30 where the sensitivity of 43.8%, specificity of 64%, and an accuracy of 56.1% were recorded. ORi and SpO2 correlation was found at DS5, 5 min after lateral position with two-lung ventilation (DL5) and at 10 min after OLV (OLV10) (p = 0.044, p = 0.039, p = 0.011, respectively). Time-dependent correlations also showed that; at a time point of DS5, ORi has a significant negative correlation with PI whereas, no correlations with PVI were noted.

Conclusions

During the use of OLV for thoracic surgeries, from 5 min after intubation (DS5) up to 30 min after the start of OLV, ORi provides valuable information in predicting hypoxemia defined as SpO2 less than 95% on pulse oximeter at FiO2 higher than 50%.

ORi™: a new indicator of oxygenation

In the perioperative period, hypoxemia and hyperoxia are crucial factors that require attention, because they greatly affect patient prognoses. The pulse oximeter has been the only noninvasive monitor that can be used as a reference of oxygenation in current anesthetic management; however, in recent years, a new monitoring method that uses the oxygen reserve index (ORi™) has been developed by Masimo Corp. ORi is an index that reflects the state of moderate hyperoxia (partial pressure of arterial oxygen [PaO2] between 100 and 200 mmHg) using a non-unit scale between 0.00 and 1.00. ORi monitoring performed together with percutaneous oxygen saturation (SpO2) measurements may become an important technique in the field of anesthetic management, for measuring oxygenation reserve capacity. By measuring ORi, it is possible to predict hypoxemia and to detect hyperoxia at an early stage. In this review, we summarize the method of ORi, cautions for its use, and suitable cases for its use. In the near future, the monitoring of oxygen concentrations using ORi may become increasingly common for the management of respiratory function before, after, and during surgery.

Oxygen Reserve Index: Utility as an Early Warning for Desaturation in High-Risk Surgical Patients

BACKGROUND

Perioperative pulse oximetry hemoglobin saturation (Spo2) measurement is associated with fewer desaturation and hypoxia episodes. However, the sigmoidal nature of oxygen-hemoglobin dissociation limits the accuracy of estimation of the partial pressure of oxygen (Pao2) >80 mm Hg and correspondingly limits the ability to identify when Pao2 >80 mm Hg but falling. We hypothesized that a proxy measurement for oxygen saturation (Oxygen Reserve Index [ORI]) derived from multiwavelength pulse oximetry may allow additional warning time before critical desaturation or hypoxia. To test our hypothesis, we used a Masimo multiwavelength pulse oximeter to compare ORI and Spo2 warning times during apnea in high-risk surgical patients undergoing cardiac surgery.

METHODS

This institutional review board-approved prospective study (NCT03021473) enrolled American Society of Anesthesiologists physical status III or IV patients scheduled for elective surgery with planned preinduction arterial catheter placement. In addition to standard monitors, an ORI sensor was placed and patients were monitored with a pulse oximeter displaying the ORI, a nondimensional parameter that ranges from 0 to 1. Patients were then preoxygenated until ORI plateaued. Following induction of anesthesia, mask ventilation with 100% oxygen was performed until neuromuscular blockade was established. Endotracheal intubation was accomplished using videolaryngoscopy to confirm placement. The endotracheal tube was not connected to the breathing circuit, and patients were allowed to be apneic. Ventilation was resumed when Spo2 reached 94%. We defined ORI warning time as the time from when the ORI alarm registered (based on the absolute value and the rate of change) until the Spo2 decreased to 94%. We defined the Spo2 warning time as the time for Spo2 to decrease from 97% to 94%. The added warning time provided by ORI was defined as the difference between ORI warning time and Spo2 warning time.

RESULTS

Forty subjects were enrolled. Complete data for analysis were available from 37 patients. The ORI alarm registered before Spo2 decreasing to 97% in all patients. Median (interquartile range [IQR]) ORI warning time was 80.4 seconds (59.7-105.9 seconds). Median (IQR) Spo2 warning time was 29.0 seconds (20.5-41.0 seconds). The added warning time provided by ORI was 48.4 seconds (95% confidence interval [CI], 40.4-62.0 seconds; P < .0001).

CONCLUSIONS

In adult high-risk surgical patients, ORI provided clinically relevant added warning time of impending desaturation compared to Spo2. This additional time may allow modification of airway management, earlier calls for help, or assistance from other providers. The potential patient safety impact of such monitoring requires further study.

The Oxygen Reserve Index as a determinant of the necessary amount of postoperative supplemental oxygen

BACKGROUND

Although blood gas analysis (BGA) is important for supplemental oxygen titration, it is invasive, intermittent, costly, and burdensome for staff. We assessed whether the Oxygen Reserve Index (ORi™), a novel pulse oximeter-based index that reflects the partial pressure of oxygen (PaO<inf>2</inf>), could determine the amount of postoperative supplemental oxygen. We also evaluated the extent of hyperoxia and hypoxia.

METHODS

Fifty patients scheduled to undergo breast surgery were randomly assigned to receive ORi-based oxygen (group O) or conventional postoperative oxygen (group C) treatments. Postoperatively, patients were transported to the Post-Anesthesia Care Unit (PACU) and then to general wards. In group O, oxygen was administered at 4 L·min^-1 in the operation room after extubation and was decreased if the ORi was >0.00 until a continuous index of 0.00 was achieved for 30 min in the PACU and wards. In group C, oxygen was administered at 4 L·min^-1 throughout the evaluation period. BGA was performed 1 h after anesthesia induction (T0), after extubation (T1), before PACU exit (T2), and on the first postoperative morning (T3). Percutaneous oxygen saturation was measured every two seconds from 9 PM after surgery to 6 AM the next morning.

RESULTS

The supplemental oxygen amount and PaO<inf>2</inf> were significantly lower in group O than group C at T2 (1.5 [0.5-3.0] vs. 4.0 [4.0-4.0] L/min, 117.3 [26.8] vs. 170.0 [42.8] mmHg) and T3 (1.0 [0.5-3.0] vs. 4.0 [4.0-4.0] L/min, 107.5 [16.5] vs. 157.1 [28.4] mmHg; median [interquartile ranges] and mean [1 SD]; P<0.01). No patient exhibited hypoxia.

CONCLUSIONS

Based on our results, ORi might be useful to titrate postoperative oxygen supplementation.

Oxygen reserve index, a new method of monitoring oxygenation status: what do we need to know?

The oxygen reserve index (ORI) is a new technology that provides real-time, non-invasive, and continuous monitoring of patients’ oxygenation status. This review aimed to discuss its clinical utility, prospect and limitations. A systematic literature search of PubMed, MEDLINE, Google Scholar, and ScienceDirect was performed with the keywords of “oxygen reserve index,” “ORI,” “oxygenation,” “pulse oximetry,” “monitoring,” and “hyperoxia.” Original articles, reviews, case reports, and other relevant articles were reviewed. All articles on ORI were selected. ORI can provide an early warning before saturation begins to decrease and expands the ability to monitor the human body's oxygenation status noninvasively and continuously with the combination of pulse oximetry so as to avoid unnecessary hyperoxia or unanticipated hypoxia. Although the technology is so new that it is rarely known and has not been applied to routine practices in hospitals, it shows good prospects for critical care, oxygen therapy, and intraoperative monitoring.

Intraoperative Anesthetic Management of the Thoracic Patient

The intraoperative anesthetic management for thoracic surgery can impact a patient's postoperative course, especially in patients with significant lung disease. One-lung ventilation poses an inherent risk to patients, including hypoxemia, acute lung injury, and right ventricular dysfunction. Patient-specific ventilator management strategies during one-lung ventilation can reduce postoperative morbidity.

Study of early warning for desaturation provided by Oxygen Reserve Index in obese patients

Acute hemoglobin desaturation can reflect rapidly decreasing PaO₂. Pulse oximetry saturation (SpO₂) facilitates hypoxia detection but may not significantly decrease until PaO₂ < 80 mmHg. The Oxygen Reserve Index (ORI) is a unitless index that correlates with moderately hyperoxic PaO₂. This study evaluated whether ORI provides added arterial desaturation warning in obese patients. This IRB approved, prospective, observational study obtained written informed consent from Obese (body mass index (BMI) kg m^-2; 30 < BMI < 40) and Normal BMI (19 < BMI < 25) adult patients scheduled for elective surgery requiring general endotracheal anesthesia. Standard monitors and an ORI sensor were placed. Patient's lungs were pre-oxygenated with 100% FiO₂. After ORI plateaued, general anesthesia was induced, and endotracheal intubation accomplished using a videolaryngoscope. Patients remained apneic until SpO₂reached 94%. ORI and SpO₂ were recorded continuously. Added warning time was defined as the difference between the time to SpO₂ 94% from ORI alarm start or from SpO₂ 97%. Data are reported as median; 95% confidence interval. Complete data were collected in 36 Obese and 36 Normal BMI patients. ORI warning time was always longer than SpO₂ warning time. Added warning time provided by ORI was 46.5 (36.0-59.0) seconds in Obese and 87.0 (77.0-109.0) seconds in Normal BMI patients, and was shorter in Obese than Normal BMI patients difference 54.0 (38.0-74.0) seconds (p < 0.0001). ORI provided what was felt to be clinically significant added warning time of arterial desaturation compared to SpO₂. This added time might allow earlier calls for help, assistance from other providers, or modifications of airway management.Trial registration ClinicalTrials.gov NCT03021551.