Oxygen reserve index to early detect desaturation in apnea dogs

Oxygen status can be monitored using pulse oximetry, that estimates the percentage of oxygen- saturated hemoglobin (SpO2). However, SpO2 provides limited information in hyperoxemic patients, remaining >98% for arterial partial oxygen pressure (PaO2) >100mmHg [1]. The Oxygen Reserve index (ORi) is a new real-time continuous index measured with a multi-wavelength pulse co-oximetry technology, which ranges from 0 to 1, and estimates PaO2 between 100 and 200 mmHg in humans [2]. Also in dogs, ORi has been shown to be positively correlated with PaO2 and able to detect mild hyperoxemia [3]. Providing a non-invasive indication of PaO2>100mmHg, ORi might identify an impending desaturation earlier than SpO2 [4]. The aim of this study is to evaluate the ability of ORi to early detect desaturation in apneic dogs at recovery from anesthesia. This prospective observational study enrolled 71 non-obese owned-client anesthetized dogs. Animals were mechanically ventilated maintaining a fraction of inspired oxygen (FiO2) 0.50 for elective procedures. At the end of the procedure, ORi value was measured using a multi- wavelength pulse co-oximeter with a probe applied to the dog’s tongue. After detecting an ORi value of 1, dogs were maintained intubated, the administration of oxygen mixture was interrupted, and SpO2 and ORi simultaneously monitored. Time was recorded from ORi 0.9 to SpO2 95%, from ORi 0.5 to SpO2 95%, and from SpO2 98% to SpO2 95% and defined as “ORi0.9dec” “ORi0.5dec” and SpO2dec”, respectively. Only dogs that remained apneic until SpO2 95% were included. When SpO2 reached 95%, animals were mechanically ventilated with pure oxygen for at least 2 minutes. Apneic dogs were 38 (19 males and 19 females), with median (min-max) weight of 14.1 (4.2-30.0) Kg and age of 75 (8-168) months. In all patients ORi was 1 at the end of the elective procedure. In each dog, ORi decreased from 1 to 0 in a median (min-max) time of 131.5 (8-456) sec, while SpO2 remained 398%. Median (min-max) “ORi0.9dec”, “ORi05dec”, and “SpO2dec” were 63 (10-586), 33 (5-290) sec and 7 (1-154) sec, respectively. Therefore, in apneic dogs, the decrease in oxygen blood content is detected earlier by ORi than by SpO2. ORi decrease time might provide added arterial desaturation warning in apneic dogs and could prevent a possible worsening oxygen status, allowing for safe management of recovery. [1] Chan ED, Chan MM. Pulse oximetry: understanding its basic principles facilitates appreciation of its limitations. Respir Med, 107(6); 789-799, 2013 [2] Scheeren TWL et al. The oxygen reserve index (ORI): a new tool to monitor oxygen therapy. J Clin Monit Comput, 32(3); 379-389, 2018 [3] Zanusso F et al. The ability of oxygen reserve index to detect mild hyperoxemia in mechanically ventilated dogs: a preliminary study. European Veterinary Emergency and Critical Care Congress, 1-3 June 2023, Porto, Portugal [4] Tsymbal E et al. Study of early warning for desaturation provided by Oxygen Reserve Index in obese patients. J Clin Monit Comput, 35(4); 749–756, 2021