Evaluation of oxygen reserve index as an early warning indicator of hypoxemia in anesthetized dogs.

Abstract

The oxygen reserve index (ORi) is a non-invasive parameter recently introduced in human medicine that detects impending hypoxemia earlier than peripheral oxygen saturation (SpO). This study evaluated the utility of ORi as an early warning indicator of hypoxemia in anesthetized dogs. Six beagle dogs were subjected to planned apnea under two oxygen conditions (FiO1.0 and 0.4). Changes in ORi, SpO, and arterial oxygen partial pressure (PaO) were monitored. Warning times (WT) were calculated as the time difference between each timepoint and SpOreaching 90%. We defined Added warning times (AWT) as the time between an ORi warning point and the moment SpOfell to 96%. When ORi decreased to half of its baseline value or reached 0.4, it provided early warnings of 43.2 &#xb1; 24.6 sec and 44.7 &#xb1; 37.0 sec, under FiO1.0, and 29.5 &#xb1; 21.9 sec and 37.0 &#xb1; 22.5 sec under FiO0.4, before SpObegan to decrease. A significant positive correlation was observed between ORi and PaOwhen SpOwas &#x2265;97% (r=0.74, P<0.0001). Receiver operating characteristic (ROC) analysis showed high diagnostic accuracy of ORi for predicting PaO&#x2265;150 mmHg (area under the curve [AUC]=0.92), with an optimal cutoff value of 0.48 (sensitivity 92%, specificity 78.8%). Unlike in humans, ORi continued to change at PaOlevels above 200 mmHg in dogs, suggesting species-specific differences. In conclusion, ORi can detect deterioration in oxygenation earlier than SpOin anesthetized dogs and provides valuable non-invasive real-time monitoring of oxygen reserves during controlled apnea under anesthesia.