Flow-controlled expiration improves gas exchange in anaesthetised horses undergoing orthopaedic surgery.

Abstract

BACKGROUND: Flow-controlled expiration (FLEX) has been shown to significantly enhance oxygenation in horses under laboratory conditions. OBJECTIVE: This study aims to corroborate these findings by evaluating the effects of FLEX on gas exchange in a randomised clinical trial involving a large population of clinical horses undergoing orthopaedic surgery. STUDY DESIGN: Prospective randomised clinical trial. METHODS: A total of 406 healthy adult horses scheduled for elective orthopaedic procedures were recruited for this prospective clinical trial. Horses were randomly assigned to FLEX or VCV (volume-controlled ventilation) groups in dorsal (VCV-D and FLEX-D) or lateral recumbency (VCV-L and FLEX-L). Arterial blood gases were measured at 30, 75, and 120&#x2009;min post-induction to assess arterial oxygenation (arterial partial pressure of oxygen to inspired fraction of oxygen ratio, PaO/FiO). A global index of ventilation/perfusion matching ([PaCO&#x2009;-&#x2009;ETCO]/PaCO) was also calculated. Peak airway pressure (P) and tidal volume were measured to calculate dynamic respiratory system compliance (Cdyn). Data were compared with repeated-measures ANOVA. RESULTS: Horses ventilated with FLEX showed significantly higher PaO/FiO(FLEX-D vs. VCV-D, 369&#x2009;&#xb1;&#x2009;42 vs. 198&#x2009;&#xb1;&#x2009;112&#x2009;mmHg, p&#x2009;<&#x2009;0.001; FLEX-L vs. VCV-L, 436&#x2009;&#xb1;&#x2009;38 vs. 249&#x2009;&#xb1;&#x2009;88&#x2009;mmHg, p&#x2009;<&#x2009;0.001). FLEX also improved Cdyn (FLEX-D vs. VCV-D, 0.81&#x2009;&#xb1;&#x2009;0.1 vs. 0.64&#x2009;&#xb1;&#x2009;0.12, p&#x2009;=&#x2009;0.01) and the global V&#x307;/Q&#x307; index ([PaCO&#x2009;-&#x2009;ETCO]/PaCO) (FLEX-D vs. VCV-D, 0.11&#x2009;&#xb1;&#x2009;0.03 vs. 0.18&#x2009;&#xb1;&#x2009;0.03, p&#x2009;=&#x2009;0.03) in dorsal-positioned but not lateral-positioned horses. MAIN LIMITATIONS: Anaesthesia protocols were not standardised; anaesthetists were not masked to the intervention of interest, and findings may not be generalisable to other patient populations. CONCLUSIONS: These results confirm previous laboratory findings, demonstrating that FLEX improves oxygenation, ventilation-perfusion matching, and respiratory mechanics compared to VCV in a large clinical population of anaesthetised horses.