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

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.

Rapid sequence induction of anesthesia: works in progress and steps forward with focus to oxygenation and monitoring techniques

The description of the main scientifically consolidated innovations in recent years on Rapid Sequence Induction have been the subject of this narrative review. Data sources were PubMed, EMBASE, Web of Science, the Cochrane Central Register of Controlled Trials, and ClinicaTrials.gov, searched up to March 21st, 2023; rapid sequence induction and anesthesia were used as key word for the research. In recent years at least three significant innovations which have improved the procedure: firstly the possibility of using drugs which rapidly reverse the action of the myorelaxants and which have made it possible to give up the use of succinylcholine, replaced by rocuronium; secondly, the possibility of using much more effective pre-oxygenation methods than in the past, also through apneic oxygenation techniques which allow longer apnea time, and finally new monitoring systems much more effective than pulse oximetry in identifying and predicting periprocedural hypoxemia and indicating the need for ventilation in patients at risk of hypoxemia and preventing it. The description of three main scientifically consolidated innovations in recent years, in pharmacology, oxygen method of administration and monitoring, have been the subject of this narrative review.

Investigation of the association between oxygen reserve index and arterial partial oxygen pressure in anesthetized dogs

OBJECTIVE

To evaluate the relationship between oxygen reserve index (ORI) and arterial partial pressure of oxygen (PaO2) in anesthetized dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of eight healthy adult Beagle dogs with a median age of 38 (range 20-87) months and a median body mass of 8.6 (range 7.0-13.8) kg.

METHODS

After induction of general anesthesia with propofol, dogs were mechanically ventilated and anesthesia maintained with isoflurane carried in oxygen. Arterial blood samples were collected from a catheter placed in the femoral artery. ORI was measured by placing a CO-oximeter sensor on the tongue. Inspired oxygen fraction (FiO2) was increased from 21% to > 95% in increments of 5%. PaO2 and ORI were recorded and compared at different times. The relationship between ORI and PaO2 was investigated using a nonlinear function, the Hill equation, and a linear regression analysis was performed, as appropriate.

RESULTS

A total of 128 pairs of values were compared for all dogs. Applying the Hill equation to the relationship between ORI and PaO2 resulted in R2 = 0.80 (p < 0.001) with a Hill coefficient of 3.7. It was predicted that ORI ranged 0.1-0.9 as PaO2 ranged 127.0-417.9 mmHg and that in the more linear portion of the range, PaO2 of 127.0-289.9 mmHg ORI ranged 0.1-0.7. Linear regression analysis in the more linear portion showed a weak correlation (R2 = 0.29, p = 0.006).

CONCLUSIONS AND CLINICAL RELEVANCE

In the present study, the Hill equation predicted the relationship between PaO2 and ORI for PaO2 ranging 127.0-417.9 mmHg in anesthetized dogs. However, in the linear portion of the PaO2, the coefficient of determination was low, indicating that ORI is not a surrogate for PaO2.

Perioperative monitoring of the oxygen reserve: where do we stand?

The Oxygen Reserve Index (ORi) is an advanced plethysmography-derived variable that may help to quantify the degree of hyperoxia in patients receiving supplemental oxygen administration. ORi is a (relative) indicator of the actual partial pressure of oxygen dissolved in arterial blood (PaO2). As such, it may help in the titration of oxygen administration or it may help to warn the clinician of a deterioration of oxygen status of the patient.In this issue of the journal, Fadel et al. provide a 'classical' clinical validation study by assessing the correlation between ORi and PaO2 in patients about to undergo open-heart surgery. Within the moderate hyperoxic range (100-200 mmHg PaO2), there is a sound correlation between ORi and PaO2. This editorial discusses the clinical implications of this validation study and elaborates on the possible role of ORi monitoring in addition to SpO2 (peripheral arterial oxygen saturation) monitoring alone.

Comparison of oxygen reserve index according to the remimazolam or dexmedetomidine for intraoperative sedation under regional anesthesia-A single-blind randomized controlled trial

Introduction

We aimed to evaluate the difference in intraoperative oxygen reserve index (ORi) between the sedatives remimazolam (RMMZ) and dexmedetomidine (DEX).

Methods

Seventy-eight adult patients scheduled for sedation under regional anesthesia were randomly assigned to either the DEX (n = 39) or RMMZ (n = 39) group. The primary outcome was the difference in perioperative ORi between the groups. The secondary outcomes included respiratory depression, hypo- or hypertension, heart rate (HR), blood pressure, respiratory rate and postoperative outcomes. Additionally, the number of patients who experienced a decrease in intraoperative ORi to < 50% and the associated factors were analyzed.

Results

The ORi was significantly higher in the RMMZ group at 15 min after sedation maintenance. There were no significant differences in respiratory depression between the two groups. The intraoperative HR was significantly higher in the RMMZ group after the induction of sedation, 15 min after sedation maintenance, and at the end of surgery. No other results were significantly different between the two groups. The incidence of a decrease in intraoperative ORi to < 50% was significantly higher in the DEX group. Factors associated with a decrease in the intraoperative ORi to < 50% were diabetes mellitus, low baseline peripheral oxygen saturation (SpO2), and DEX use. In the receiver operating characteristic curve analysis for a decrease in the intraoperative ORi to < 50%, the cutoff baseline SpO2 was 97%.

Conclusion

RMMZ is recommended as a sedative for patients with a low baseline SpO2 and intraoperative bradycardia. Further studies should be conducted to establish the criteria for a significant ORi reduction.

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.

Hypoxia as a potential cause of dyspareunia

Dyspareunia is genital pain before, during or after penile-vaginal sexual intercourse. The prevalence of dyspareunia ranges from 8 to 22%. Sexual intercourse concomitant with a pelvic organic lesion is likely to cause pain in most cases. However, in these cases, the pain depends not only on sexual intercourse. In its basic definition, dyspareunia in women is considered an idiopathic affection without a typical organic constitution. It is only present with penile-vaginal penetration. Long-term hypoxia in perineal muscles can cause muscle and perimuscular changes, leading to chronic pain not sufficiently responding to standard therapy. During the entrance examination to our previous study on dyspareunia, we noted significantly lower pulse oximetry levels in the perineal area of affected women. We aimed to compare pulse oximetry oxygen saturation (SpO2) of dyspareunia-affected women to healthy, pain-free women. A retrospective study was performed. The study participants were women who had participated in our previously published study on dyspareunia. This retrospective study was approved by the Ethical Committee. The study included 62 women: 31 dyspareunia-affected women in the treatment group and 31 healthy women in the control group.

METHOD

During their examinations, women in the dyspareunia and control groups were measured for SpO2. The procedure was performed in the vulvo-perineal rear region, involving the commissure and the bulbospongiosus muscle. Median and mean SpO2 were compared between the treatment and control groups. Testing for sample size accuracy was performed retroactively.

RESULTS

There were 31 participants in each group. The SpO2 data were skewed and did not follow a Gaussian distribution. The Mann-Whitney U test was run to determine differences in perineum oximetry between the treatment group and controls. The median SpO2 was 91 in the treatment group and 92 in the control group. This difference was statistically significant, p = 0.002. Sample size accuracy was assured by post hoc calculation.

CONCLUSIONS

Idiopathic dyspareunia is inherent in cohabitation muscle pain that standard therapy could not explain nor treat. We detected clinically meaningfully decreased levels of SpO2 in affected patients. We compared pelvic oximetry between dyspareunia-affected women in the treatment and control groups. This comparison showed significant hypoxia in the perineal muscle area (p = 0.002). Our results may help us understand the source of this pain and guide treatment accordingly.

[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.

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.

Awake craniotomy using a high-flow nasal cannula with oxygen reserve index monitoring - A report of two cases

BACKGROUND

Awake craniotomy is a well-tolerated procedure for the resection of brain tumors residing within or close to the eloquent cortical areas. Monitored anesthesia care (MAC) is a dominant anesthetic approach for awake craniotomy; however, it is associated with inherent challenges such as desaturation and hypercapnia, which may lead to various complications. The prevention of respiratory insufficiency is important for successful awake craniotomy. As measures to avoid respiratory depression, the use of high-flow nasal cannula (HFNC) can improve patient oxygenation and monitor the monitoring the oxygen reserve index (ORi) can detect hypoxia earlier.

CASE

We report two cases of awake craniotomy with MAC using HFNC and ORi. We adjusted the fraction of inspired oxygen of the HFNC according to the ORi level. The patient underwent successful awake craniotomy without a desaturation event or additional airway intervention.

CONCLUSIONS

Combined HFNC and ORi monitoring may provide adequate oxygen reserves in patients undergoing awake craniotomy.

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).

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 for non-invasive early hypoxemia detection during endotracheal intubation in intensive care: the prospective observational NESOI study

Background

To evaluate the ability of the oxygen reserve index (ORI) to predict the occurrence of mild hypoxemia (defined as SpO₂  <  97%) during endotracheal intubation (ETI) of patients in the intensive care unit (ICU).

Methods

This observational single-centre study included patients without hypoxemia (defined as SpO₂/FiO₂  >  214) who required ETI in the ICU. Patients were followed during preoxygenation and ETI then until hospital discharge and/or day 28. We recorded cases of mild hypoxemia, moderate (SpO₂  <  90%) and severe (SpO₂  <  80%) hypoxemia, moderate arterial hypotension (systolic arterial pressure  <  90 mmHg), oesophageal intubation, aspiration, cardiac arrest, and death.

Results

Between January 2019 and July 2020, 56 patients were included prospectively and 51 patients were analysed. Twenty patients had mild hypoxemia between the end of preoxygenation and the end of intubation; in 10 of these patients, the decrease in SpO₂ below 97% was preceded by an ORI  <  0.4, the median time difference being 81 s [interquartile range, 34–146]. By multivariable analysis, a higher ORI (by 0.1 increase) value during preoxygenation was associated with absence of hypoxemia (odds ratio, 0.76; 95% confidence interval, 0.61;0.95; P  =  0.0141).

Conclusion

In non-hypoxemic patients, the 81-s [34–146] median time between the ORI decrease below 0.4 and the SpO₂ decrease below 97% during apnoea may allow preventive action. A higher ORI value during preoxygenation was independently protective against hypoxemia. Whether these findings also apply to hypoxemic patients, and the clinical impact of a preoxygenation strategy based on ORI monitoring, remain to be evaluated prospectively.

Trial Registration ClinicalTrial.gov, #NCT03600181.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00903-8.