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Oxygen Reserve Index: Validation of a New Variable

Vos, Jaap Jan MD, PhD*; Willems, Cornelis H. MD*; van Amsterdam, Kai MSc*; van den Berg, Johannes P. MD*; Spanjersberg, Rob*; Struys, Michel M. R. F. MD, PhD, FRCA*,†; Scheeren, Thomas W. L. MD, PhD*

doi: 10.1213/ANE.0000000000003706
Technology, Computing, and Simulation: Original Clinical Research Report

BACKGROUND: Pulse oximetry–derived oxygen saturation is typically >97% in normoxia and hyperoxia, limiting its clinical use. The new Oxygen Reserve Index (ORi), a relative indicator of the partial pressure of oxygen dissolved in arterial blood (Pao2) in the range of 100–200 mm Hg, may allow additional monitoring of oxygen status.

METHODS: In this prospective validation intervention study, 20 healthy volunteers were breathing standardized oxygen concentrations ranging from mild hypoxia (fraction of inspired oxygen = 0.14) to hyperoxia (fraction of inspired oxygen = 1.0) via a tight-fitting face mask. ORi was measured noninvasively by multiwavelength pulse co-oximetry using 2 finger sensors. These ORi values (unitless scale, 0.00–1.00) were compared with measured Pao2 values. Repeated-measurements correlation analysis was performed to assess the ORi/Pao2 relationship. ORi trending ability was assessed using a 4-quadrant plot. The area under the receiver operating characteristics curve was calculated to assess the prediction of hypoxia (low-ranged Pao2, <100 mm Hg).

RESULTS: Within the ORi-sensitive range, a strong positive correlation was found between ORi and Pao2 for both sensors (R = 0.78 and 0.83; P < .0001). ORi trending of Pao2 was good within this range (concordance rate = 94%). The prediction of Pao2 <100 mm Hg was also good, with an area under the receiver operating characteristics curve of 0.91 and 99% sensitivity and 82% specificity.

CONCLUSIONS: 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.

From the *Department of Anesthesiology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands

Department of Anesthesia and Perioperative Medicine, Ghent University, Gent, Belgium.

Published ahead of print 3 July 2018.

Accepted for publication July 3, 2018.

C. H. Willems is currently affiliated with the Wilhelmina Hospital, Assen, the Netherlands.

Funding: This study was funded by Masimo Corp, Irvine, CA. M.M.R.F.S. and his research group/department received grants and funding from The Medicines Company (Parsippany, NJ), Masimo Corp (Irvine, CA), Fresenius (Bad Homburg, Germany), Acacia Design (Maastricht, the Netherlands), and Medtronic (Dublin, Ireland).

Conflicts of Interest: See Disclosures at the end of the article.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Clinical trial number: (Ref: NCT02561052).

Reprints will not be available from the authors.

Address correspondence to Jaap Jan Vos, MD, PhD, Department of Anesthesiology, University of Groningen, University Medical Center Groningen, PO Box 30 001, 9700 RB Groningen, the Netherlands. Address e-mail to

Copyright © 2018 International Anesthesia Research Society
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