Effects of flow‐controlled expiration on oxygenation and early recovery in horses undergoing general anaesthesia

Background FLow‐controlled EXpiration (FLEX) has been shown to significantly enhance oxygenation in horses under clinical and experimental conditions. Objectives To compare pulmonary gas exchange during early recovery following general anaesthesia in horses ventilated with FLEX compared with conventional intermittent positive pressure ventilation (IPPV) and to assess recovery characteristics between ventilation modes. Study Design Randomised, crossover in vivo experiments. Methods Six adult horses underwent two 2‐h anaesthetic episodes in a randomised crossover design (FLEX vs. IPPV), separated by a two‐week washout. Arterial blood gases were analysed at 60‐ and 120‐min post‐induction. Arterial blood pressure, end‐tidal inhalant concentrations, respiratory rate, and haemoglobin oxygen saturation were recorded in 5‐min intervals during anaesthesia. The initial recovery period was defined as the first 20 min following return of spontaneous ventilation, during which arterial blood gases, end‐tidal inhalant concentrations, and oxygen saturation were recorded in 5‐min intervals. Horses were recovered using head and tail rope assistance. The time to sternal recumbency, standing, and the number of standing attempts were recorded. Data were analysed using linear mixed‐effects models for repeated measures and paired tests for recovery outcomes. Results PaO 2 was higher during general anaesthesia with FLEX (mean ± SD: 422 ± 24 vs. 202 ± 101 mmHg at 60 min; 433 ± 31 vs. 180 ± 59 mmHg at 120 min; p < 0.01). In recovery, PaO 2 remained higher with FLEX (20 min: 114 ± 21 vs. 62 ± 11 mmHg; p < 0.01) and EtIso declined more rapidly ( p < 0.01). Time to sternal and standing were shorter and attempts to stand fewer with FLEX (exploratory outcomes). Main Limitations This study enrolled a small sample size, which may limit generalisability. Recovery was recorded from one camera angle, potentially restricting full assessment of recovery behaviour. No respiratory mechanics or regional ventilation distribution were quantified. Conclusions FLEX improves oxygenation during early recovery and is associated with faster recovery times in healthy horses.