Evaluation of the Effect of the Inspired Oxygen Fraction on Blood Oxygenation during Inhalant Anaesthesia in Horses: A Systematic Review with Meta-Analysis.
Authors: Savvas Ioannis, Pavlidou Kiriaki, Braun Christina, Schauvliege Stijn, Staffieri Francesco, Moens Yves
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Absorption atelectasis—the collapse of alveoli supplied by poorly ventilated airways—represents a significant concern during equine inhalant anaesthesia, yet controversy persists regarding optimal inspired oxygen fractions (FiO2) to mitigate this complication whilst maintaining adequate oxygenation. This systematic review and meta-analysis examined five studies to compare the effects of low FiO2 (<0.6) versus high FiO2 (>0.8) on arterial oxygen tension (PaO2), the alveolar-to-arterial oxygen gradient (P(A-a)O2), and the PaO2/FiO2 ratio—all key indicators of pulmonary gas exchange efficiency in anaesthetised horses. The meta-analysis of four experimental studies revealed that whilst higher FiO2 delivered significantly higher absolute PaO2 values (23.54 kPa mean difference), the critical finding was that lower FiO2 strategies also produced a markedly reduced P(A-a)O2 difference (20.80 kPa lower, p<0.00001), suggesting improved ventilation-perfusion matching and less pathological shunting. For equine practitioners, this indicates a nuanced trade-off: high-oxygen protocols guarantee higher arterial oxygen levels but paradoxically worsen the physiological efficiency of oxygen transfer across the alveolar membrane, whereas lower FiO2 may optimise pulmonary mechanics despite modestly lower blood oxygen content. The authors acknowledge substantial limitations in the current evidence base and call for additional clinical trials to establish best-practice oxygen dosing protocols in horses undergoing inhalant anaesthesia.
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Practical Takeaways
- •Higher oxygen fractions improve arterial oxygen levels during horse anaesthesia, but may increase the oxygen gradient difference reflecting worse matching of ventilation to perfusion
- •Lower oxygen fractions may help reduce absorption atelectasis formation during equine anaesthesia, but at the cost of lower blood oxygen levels
- •Current evidence is insufficient to definitively recommend one FiO2 strategy over another for routine equine anaesthetic practice; clinical judgment should guide oxygen supplementation decisions
Key Findings
- •Lower FiO2 (<0.6) resulted in significantly lower arterial oxygen tension (PaO2) by mean 23.54 kPa compared to higher FiO2 (>0.8)
- •Lower FiO2 also significantly reduced alveolar-to-arterial oxygen tension difference (P(A-a)O2) by mean 20.80 kPa, suggesting reduced ventilation/perfusion mismatching
- •Higher FiO2 produces higher PaO2 levels but with larger P(A-a)O2 differences during equine inhalation anaesthesia
- •Limited evidence base with only 5 studies identified (4 experimental, 1 clinical) demonstrates need for further research