Study evaluates ability of Masimo Ori to detect declining blood oxygenation during one-lung ventilation

Masimo announced today the findings of a study in which researchers evaluated the ability of Masimo ORi^™ (Oxygen Reserve Index) to detect declining blood oxygenation prior to standard oxygen saturation (SpO₂) monitoring in patients undergoing elective thoracic surgery requiring one-lung ventilation (OLV).

ORi is a noninvasive, relative indicator of a patient's oxygen reserve in the moderate hyperoxic region (partial pressure of oxygen in arterial blood [PaO₂] in the range of 100 to 200 mmHg). As an "index" parameter with a unit-less scale between 0 and 1, ORi can be trended and has optional alarms to notify clinicians of changes in a patient's oxygen reserve.

In the study, Dr. Koishi and colleagues at Iwate Medical University in Morioka, Japan sought to evaluate whether ORi could serve as an early warning of desaturation in patients undergoing OLV, as such patients are often prone to hypoxemia. To this end, they assessed whether ORi decreased earlier than SpO₂ during OLV, and evaluated how well ORi correlated with an invasive PaO₂ measurement. ORi and SpO₂ were measured every 2 seconds using a Masimo Root^® with Radical-7^® Pulse CO-Oximeter^® and rainbow^® sensors (revision L). The anesthesiologist was blinded to the ORi values. For data analysis, the researchers defined the start of the decrease in ORi as when its value fell below 0.05 less than its highest value after OLV began, and the start of the decrease in SpO₂ as when it was 1% less than the maximum SpO₂ value. PaO₂ was calculated as part of blood gas analysis and performed every 3 minutes during OLV, resulting in 101 pairs of measurements.

The researchers found that from the start of OLV, ORi started decreasing significantly sooner than SpO₂, a mean of 171 seconds vs. a mean of 372 seconds, p<0.01 (standard deviation of 102 and 231 seconds, respectively). They also found "a significant, strong correlation" between ORi and PaO₂: r²=0.671, p<0.01.

The researchers concluded, "ORi decreased significantly earlier than SpO₂ during OLV, suggesting that monitoring ORi might allow earlier detection of a deterioration of blood oxygenation than monitoring SpO₂ alone, contributing to a reduction in the patient's risk of exposure to complications from OLV. However, further studies in different clinical and experimental settings are needed to evaluate the superiority of the ORi over SpO₂."

ORi has not received FDA 510(k) clearance and is not yet available for sale in the United States.