The Oxygen Reserve Index as a determinant of the necessary amount of postoperative supplemental oxygen

Although blood gas analysis (BGA) is important for supplemental oxygen titration, it is invasive, intermittent, costly, and burdensome for staff. We assessed whether the Oxygen Reserve Index (ORi™), a novel pulse oximeter-based index that reflects the partial pressure of oxygen (PaO2), could determine the amount of postoperative supplemental oxygen. We also evaluated the extent of hyperoxia and hypoxia.

Fifty patients scheduled to undergo breast surgery were randomly assigned to receive ORi-based oxygen (group O) or conventional postoperative oxygen (group C) treatments. Postoperatively, patients were transported to the Post-Anesthesia Care Unit (PACU) and then to general wards. In group O, oxygen was administered at 4 L·min^-1 in the operation room after extubation and was decreased if the ORi was >0.00 until a continuous index of 0.00 was achieved for 30 min in the PACU and wards. In group C, oxygen was administered at 4 L·min^-1 throughout the evaluation period. BGA was performed 1 h after anesthesia induction (T0), after extubation (T1), before PACU exit (T2), and on the first postoperative morning (T3). Percutaneous oxygen saturation was measured every two seconds from 9 PM after surgery to 6 AM the next morning.

The supplemental oxygen amount and PaO2 were significantly lower in group O than group C at T2 (1.5 [0.5-3.0] vs. 4.0 [4.0-4.0] L/min, 117.3 [26.8] vs. 170.0 [42.8] mmHg) and T3 (1.0 [0.5-3.0] vs. 4.0 [4.0-4.0] L/min, 107.5 [16.5] vs. 157.1 [28.4] mmHg; median [interquartile ranges] and mean [1 SD]; P<0.01). No patient exhibited hypoxia.

Based on our results, ORi might be useful to titrate postoperative oxygen supplementation.