Masimo announced today the findings of a study recently published in Anesthesia & Analgesia in which researchers at the University of Groningen, the Netherlands, and Ghent University, Belgium, investigated the ability of Masimo ORi™ (Oxygen Reserve Index) to show trends in oxygenation in the moderate hyperoxic region (partial pressure of oxygen in arterial blood [PaO2] in the range of 100 to 200 mmHg). ORi is available outside the U.S. and is intended as a noninvasive, relative indicator of a patient's oxygen reserve during moderate hyperoxia. ORi can be trended and has optional alarms to notify clinicians of changes in oxygenation.
Noting that monitoring oxygenation using pulse oximetry alone "gives little information on PaO2" during conditions of normoxia and hyperoxia, Dr. Jaap Jan Vos and colleagues sought to evaluate the correlation of ORi to PaO2 during moderate hyperoxia. They collected data from 20 healthy adult volunteers, who breathed a series of standardized oxygen concentrations ranging from mildly hypoxic (inspired oxygen = 14%) to extremely hyperoxic (inspired oxygen = 100%). ORi and SpO2 were noninvasively and continuously measured by sensors on both the second and fourth fingers and displayed on a Masimo Radical-7® Pulse CO-Oximeter®. At baseline and at each induced oxygenation stage, arterial blood samples were taken for blood gas analysis and PaO2 was measured invasively using a Siemens Rapidpoint 405 CO-Oximeter.
The researchers collected 1,090 paired data points of simultaneous ORi and PaO2 values. In the "ORi-sensitive" range of 100-200 mmHg, the mean ORi value was 0.16, with associated oxygen saturation (SpO2) values of ≥ 97% at all points. Correlation between ORi and PaO2 was positive at all points (p < 0.0001), with R values of 0.78, 0.83, and 0.84 for sensor 1, sensor 2, and mean of both sensors, respectively. To assess ORi's trending ability, the researchers used a 4-quadrant plot and calculated that ORi trending of PaO2 within the range of 100-200 mmHg had a concordance rate of 94%.
The researchers concluded, "In this prospective volunteer validation study, a strong and positive correlation between PaO2 and ORi was found, together with a good trending ability. Based on these data, the future use of ORi as a continuous noninvasive monitoring tool for assessing oxygenation status in patients receiving supplemental oxygen might be supported." They also noted that "in healthy volunteers, ORi provides reasonable trending information of PaO2 around the moderate hyperoxic range of PaO2 for which its use is intended. Also, changes in PaO2 are well reflected by changes in ORi, with good concordance. The trend in ORi can be used to track changes in PaO2 levels in the moderate hyperoxic region, and absolute values should not be interpreted for PaO2 levels."
The researchers noted several limitations of the study, including that "additional studies are required to confirm these findings in a clinical setting" and that the influence of factors such as patient comorbidity and clinical circumstances requires further research. In addition, the researchers observed differences between the absolute values of simultaneously measured ORi values from sensors placed at different sites on the subject, which may require further studies in order to clinically rely on absolute ORi values as a direct measure of oxygen reserve, especially in situations where accurate oxygenation assessment may be necessary.
Study co-author Professor Thomas Scheeren commented, "ORi fills a gap in the monitoring of patients receiving supplemental oxygen by noninvasively and continuously trending the course of arterial oxygen tension. It may help to better titrate oxygen therapy to avoid both hypoxia and unintended hyperoxia."
ORi has not received FDA 510(k) clearance and is not available for sale in the United States.