Effect of 50% and maximal inspired oxygen concentrations on respiratory variables in isoflurane-anesthetized horses.
Authors: Hubbell John A E, Aarnes Turi K, Bednarski Richard M, Lerche Phillip, Muir William W
Journal: BMC veterinary research
Summary
# Editorial Summary: Oxygen Management During Equine Anaesthesia Absorption atelectasis—the collapse of alveoli when high oxygen concentrations are rapidly absorbed into the blood—is a recognised problem during equine general anaesthesia, yet optimal inspired oxygen levels remain unclear. Hubbell and colleagues compared moderate (50%) versus maximal (>95%) oxygen supplementation in dorsally recumbent horses under isoflurane, measuring arterial oxygen tension, shunt fraction (blood bypassing ventilated lung), and systemic oxygen delivery. Moderate oxygen (FiO₂ 0.5) reduced atelectasis formation and improved ventilation-perfusion matching compared with maximal oxygen, resulting in better arterial oxygenation and oxygen delivery to tissues despite lower absolute oxygen concentrations. These findings suggest that practitioners can safely reduce inspired oxygen to 50% during routine equine anaesthesia, avoiding the counterintuitive harm caused by excessive oxygen whilst maintaining adequate systemic oxygenation—a particularly valuable consideration in lengthy procedures where absorption atelectasis accumulates. The results challenge the intuitive assumption that "more oxygen is always better" and support a more measured, physiologically informed approach to intraoperative respiratory management.
Read the full abstract on PubMed
Practical Takeaways
- •Consider using 50% oxygen during routine equine anesthesia to reduce atelectasis-related complications without compromising oxygenation
- •This oxygen protocol may improve recovery quality by maintaining better gas exchange throughout the anesthetic period
- •Consult anesthesia protocols that balance oxygen delivery with prevention of absorption atelectasis for your practice's surgical cases
Key Findings
- •50% inspired oxygen reduces absorption atelectasis compared to maximal oxygen concentrations during isoflurane anesthesia
- •50% inspired oxygen maintains adequate alveolar oxygen tension while improving ventilation-perfusion matching
- •Shunt fraction and oxygen delivery metrics were compared between oxygen concentration protocols in dorsally recumbent horses