A new study of patients undergoing elective thoracic surgery requiring one-lung ventilation (OLV) found that Oxygen Reserve Index (ORi) monitoring detected declining blood oxygenation earlier than standard oxygen saturation (SpO2) monitoring.
ORi is an investigational technology from Masimo. It is a noninvasive, relative indicator of a patient’s oxygen reserve in the moderate hyperoxic region (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.
The study, conducted by researchers 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.