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

Abstract

Pulse oximetry (SpO) identifies a decrease in the partial pressure of oxygen (PaO) when it falls below 80&#xa0;mmHg, while oxygen reserve index (ORi), a dimensionless index ranging from 0 to 1, detects PaOchanges between 100 and 200&#xa0;mmHg. This study investigates the usefulness of ORi in detecting impending deoxygenation before traditional SpO. 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&#xa0;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 SpOof 95% from ORi of 0.9 and 0.5, compared to the SpOwarning time from SpOof 98%. During apnea, ORi decreased before noticeable SpOchanges. An ORi of 0.9 anticipated an SpOof 95% in normal-fit dogs by 87 (33-212) [median (range)] seconds or in those with a BCS&#xa0;&#x2265;&#xa0;6/9 by 49 (7-161) seconds. Regardless of the BCS class, the median time from ORi of 0.5 to SpOof 95% was 30-35&#xa0;s. ORi declined from 0.9 to 0.0 in 68 compared to 33&#xa0;s between normal-fit and obese dogs (p&#xa0;<&#xa0;0.05). In dogs, ORi added warning time could facilitate timely intervention, particularly in obese patients.