Exploring oxygen reserve index for timely detection of deoxygenation in canine patients recovering from anesthesia.

Pulse oximetry (SpO ₂ ) identifies a decrease in the partial pressure of oxygen (PaO ₂ ) when it falls below 80 mmHg, while oxygen reserve index (ORi), a dimensionless index ranging from 0 to 1, detects PaO ₂ changes between 100 and 200 mmHg. This study investigates the usefulness of ORi in detecting impending deoxygenation before traditional SpO ₂ . Fifty-one dogs undergoing anesthesia were mechanically ventilated maintaining a fraction of inspired oxygen of 0.50 and an ORi of 1. Animals were classified according to their body condition score (BCS) as normal-fit (BCS 4-5/9), overweight (BCS 6-7/9), or obese (BCS 8-9/9). At the end of the procedure, dogs were placed in sternal recumbency, and after 10 min disconnected from the ventilator and maintained in apnea. ORi added warning time was determined at various ORi values as the time difference in reaching SpO ₂ of 95% from ORi of 0.9 and 0.5, compared to the SpO ₂ warning time from SpO ₂ of 98%. During apnea, ORi decreased before noticeable SpO ₂ changes. An ORi of 0.9 anticipated an SpO ₂ of 95% in normal-fit dogs by 87 (33-212) [median (range)] seconds or in those with a BCS ≥ 6/9 by 49 (7-161) seconds. Regardless of the BCS class, the median time from ORi of 0.5 to SpO ₂ of 95% was 30-35 s. ORi declined from 0.9 to 0.0 in 68 compared to 33 s between normal-fit and obese dogs (p < 0.05). In dogs, ORi added warning time could facilitate timely intervention, particularly in obese patients.
Competing Interests: Declaration of competing interest This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.
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