Oxygen reserve index : validation of a new variable

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 (Pao(2)) 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 Pao(2) values. Repeated-measurements correlation analysis was performed to assess the ORi/Pao(2) 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 Pao(2), <100 mm Hg). RESULTS: Within the ORi-sensitive range, a strong positive correlation was found between ORi and Pao(2) for both sensors (R = 0.78 and 0.83; P < .0001). ORi trending of Pao(2) was good within this range (concordance rate = 94%). The prediction of Pao(2)