Flow-controlled expiration improves gas exchange in anaesthetised horses undergoing orthopaedic surgery.
Authors: Hopster Klaus, Soares Joao Henrique Neves, Levine David, Ortved Kyla, Driessen Bernd, Araos Joaquin
Journal: Equine veterinary journal
Summary
# Editorial Summary: Flow-controlled expiration improves gas exchange in anaesthetised horses undergoing orthopaedic surgery Flow-controlled expiration (FLEX) ventilation has shown promise in laboratory settings for enhancing oxygenation during equine anaesthesia, but clinical validation remained limited. Hopster and colleagues recruited 406 healthy adult horses scheduled for elective orthopaedic procedures in a prospective randomised trial comparing FLEX against standard volume-controlled ventilation (VCV) in both dorsal and lateral recumbency positions, measuring arterial blood gases and respiratory mechanics at regular intervals throughout anaesthesia. FLEX-ventilated horses demonstrated substantially superior oxygenation across all positions (PaO2/FiO2 ratios of 369–436 mmHg versus 198–249 mmHg for VCV; p<0.001), alongside improvements in dynamic respiratory compliance and ventilation-perfusion matching in dorsally positioned animals. For anaesthetists managing orthopaedic cases, these findings suggest FLEX offers a practical means to reduce perioperative hypoxaemia risk in a large clinical population, though the lack of protocol standardisation and anaesthetist blinding warrants cautious interpretation regarding broader applicability. Implementation of FLEX protocols during routine equine orthopaedic surgery may meaningfully improve gas exchange and recovery outcomes, particularly in dorsal recumbency positions where intraoperative hypoxaemia remains a significant concern.
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Practical Takeaways
- •Consider flow-controlled expiration ventilation strategy for anaesthetised horses undergoing orthopaedic surgery to significantly improve oxygen delivery and reduce hypoxaemia risk
- •FLEX ventilation provides consistent oxygenation benefits regardless of patient positioning, with particularly strong improvements in lateral recumbency positions commonly used for surgical access
- •Switching from volume-controlled to flow-controlled expiration may be a simple, evidence-based adjustment to existing anaesthesia protocols with no apparent downside and measurable improvements in gas exchange and lung mechanics
Key Findings
- •Flow-controlled expiration (FLEX) significantly improved arterial oxygenation (PaO2/FiO2) compared to volume-controlled ventilation in both dorsal (369±42 vs 198±112 mmHg, p<0.001) and lateral recumbency (436±38 vs 249±88 mmHg, p<0.001)
- •FLEX improved dynamic respiratory system compliance (Cdyn) in dorsal-positioned horses (0.81±0.1 vs 0.64±0.12, p=0.01) but not lateral-positioned horses
- •FLEX enhanced ventilation/perfusion matching as measured by the ([PaCO2−ETCO2]/PaCO2) index in dorsal-positioned horses (0.11±0.03 vs 0.18±0.03, p=0.03)
- •Benefits of FLEX were more pronounced in lateral recumbency than dorsal recumbency for oxygenation outcomes