Study Reports on Link Between Oxygen Reserve Index by Masimo and Arterial Partial Pressure

Masimo claims a new retrospective study reports the relationship between its Oxygen Reserve Index (ORI) and arterial partial pressure of oxygen (PaO₂) during surgery. The study suggests that ORI may provide an advanced indication of impending desaturation in adults undergoing surgery based on trends in the relationship between ORI and PaO₂.¹

ORI, Masimo’s 11th rainbow parameter,² available outside of the United States, is a relative index of the PaO₂ operating in the range of 100 to 200 mm Hg. ORI can provide a calculated oxygen reserve index that may add to information from pulse oximetry when oxygen saturation (SpO₂) is > 98 percent. ORI is intended to supplement, not replace, SpO₂ monitoring and PaO₂ measurements.

In the study, published in the journal Anesthesia & Analgesia and conducted at Loma Linda University, researchers studied 106 patients in which arterial catheterization and intraoperative arterial blood gas analysis were planned during surgery. Multiwavelength Pulse CO-oximetry data from multiple sensors on each patient were continuously collected (Masimo Radical-7 with Root). A retrospective analysis was then conducted to evaluate the ORI to PaO₂ relationship.

Regression analysis showed a positive ORI to PaO₂ relationship for PaO₂ values up to 240 mm Hg (r² = 0.536), but not for PaO₂ over 240 mm Hg (r² = 0.0016). Measured PaO₂ was ≥100 mm Hg for all ORI values over 0.24, and when ORI was higher than 0.55, the measured PaO₂ was ≥150 mm Hg in 96.6 percent of samples.

The investigators concluded, “This study suggests that intraoperative ORI can distinguish PaO₂ between 100 and 150 mm Hg when SpO₂ is >98 percent. Decreases in ORI to near 0.24 may provide advance indication of falling PaO₂ when SpO₂ is still >98 percent and above the PaO₂ level at which SaO₂ [arterial oxygen saturation] declines rapidly. Usefulness of ORI >0.24 to distinguish PaO₂ ≥100 mm Hg and ORI >0.55 to distinguish PaO₂ ≥150 mm Hg should be tested prospectively in a range of clinical settings.”

Additionally, the investigators noted that “the clinical utility of interventions based on continuous ORI monitoring should also be studied prospectively,” and that other clinical or feasibility limitations may not have been identified. The authors also noted that the study was limited by a small number of subjects and samples with PaO₂ values <100 mm Hg, and that the study results did not apply to intensive care settings.

The Loma Linda University School of Medicine, Department of Anesthesiology received a grant from Masimo to support the data collection for the study.

Radical-7 with Root has a CE Mark with the ORI parameter. ORI has not received U.S. Food and Drug Administration 510(k) clearance and is not available for sale in the United States.

Masimo develops noninvasive monitoring technologies. In 1995, the company debuted Masimo SET Measure-through Motion and Low Perfusion pulse oximetry, which has been shown in multiple studies to significantly reduce false alarms and accurately monitor for true alarms. Masimo SET is estimated to be used on more than 100 million patients in leading hospitals and other healthcare settings around the world. In 2005, Masimo introduced rainbow Pulse CO-Oximetry technology, allowing noninvasive and continuous monitoring of blood constituents that previously could only be measured invasively, including total hemoglobin (SpHb), oxygen content (SpOC), carboxyhemoglobin (SpCO), methemoglobin (SpMet), and more recently, Pleth Variability Index (PVI), and Oxygen Reserve Index (ORI), in addition to SpO2, pulse rate, and perfusion index (PI). In 2014, Masimo introduced Root, an intuitive patient monitoring and connectivity platform with the Masimo Open Connect (MOC-9) interface.

References:

1. Applegate RL 2nd, Dorotta IL, Wells B, Juma D, Applegate PM. The Relationship Between Oxygen Reserve Index and Arterial Partial Pressure of Oxygen During Surgery. Anesth Analg. 2016 Mar 22. [Epub ahead of print] PubMed PMID: 27007078.
2. The 11 rainbow® parameters include: 1) oxygen saturation (SpO₂); 2) Pulse rate; 3) Perfusion index (PI); 4) Pleth Variability Index (PVI®); 5) Respiration Rate from the pleth (RRp®); 6) Total hemoglobin (SpHb®); 7) Oxygen Content (SpOC™); 8) Carboxyhemoglobin (SpCO®); 9) Methemoglobin (SpMet®); 10) Fractional oxygen saturation (SpfO2®); 11) Oxygen Reserve Index (ORI™)