Impact of low inspired oxygen fraction on oxygenation in clinical horses under general anesthesia

Abstract

Summary:The objective was to compare the use of 0.3 and >0.95 oxygen inspired fraction during general anesthesia in horses. Forty client-owned adult horses were anesthetized in dorsal or in lateral recumbency with isoflurane in oxygen and randomly allocated to receive inspiratory fraction of oxygen >0.95 (group HIGH) or 0.3 (group LOW). Mechanical ventilation was provided using pressure controlled mode. Arterial blood gas analysis was performed before, during and after general anesthesia. The group LOW obtained lower intra-operative PaO 2 values but better indices of venous admixture than the group HIGH. The PaO 2 further decreased during the recovery, without significant differences between groups. Even though the use of lower oxygen inspired fraction (0.3) tended to improve pulmonary function during general anesthesia, it markedly decreased safety as a result of hypoxemia. During the recovery, no difference was observed between groups for the arterial oxygenation such that lower intra-anesthetic oxygen inspired fraction did not provide any advantages.

Evaluation of the Effect of the Inspired Oxygen Fraction on Blood Oxygenation during Inhalant Anaesthesia in Horses: A Systematic Review with Meta-Analysis

“…In the experimental studies, isoflurane was used to maintain anaesthesia in three studies (two with mechanical ventilation [ 23 , 26 ] and one with spontaneous ventilation [ 27 ]), and halothane in one (spontaneous ventilation [ 19 ]). In the clinical trial, isoflurane was used for the maintenance of anaesthesia with mechanical ventilation [ 28 ] ( Table 1 ).…”

“…We collected and analysed data for the meta-analysis at the 90 min timepoint from all the experimental studies, which was the commonest timepoint among the studies. In the clinical study [ 28 ], data had been recorded at three timepoints during anaesthesia, and the pooled data are presented in the paper; therefore, the data were extracted for the qualitative analysis, but were not used for the meta-analysis.…”

“…In only one study [ 28 ] an a priori power analysis was performed, however the post hoc power of the study was poor.…”

Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature

“…Different studies agree that hypoxaemia occurs during recovery if oxygen is not supplemented during this phase [345,[349][350][351]. It seems that the intrapulmonary shunt produced during general anaesthesia persists in recovery while the horses remain in lateral recumbency, but oxygenation improves once they move to sternal [338,351].…”

“…The fraction of inspired oxygen (FiO 2 ) settings during general anaesthesia do not seem to affect recovery quality or the PaO 2 during recovery [340,345,348]. However, horses receiving pulsed delivery of inhaled nitric oxide (NO) during general anaesthesia had better oxygenation and ventilation perfusion (V/Q) matching during recovery [342].…”