Effects of positive end-expiratory pressure titration on intestinal oxygenation and perfusion in isoflurane anaesthetised horses.
Authors: Hopster K, Wogatzki A, Geburek F, Conze P, Kästner S B R
Journal: Equine veterinary journal
Summary
# Editorial Summary During equine anaesthesia, positive end-expiratory pressure (PEEP) recruitment improves arterial oxygenation considerably—in this 2017 study, PaO₂ increased from 201 mmHg to 495 mmHg—but the cardiovascular trade-off remains poorly understood in clinical practice. Hopster and colleagues titrated PEEP incrementally from 0 to 30 cmH₂O in ten anaesthetised horses whilst monitoring systemic and intestinal haemodynamics via thermodilution cardiac output measurement, laser Doppler flowmetry, and spectrophotometry of the stomach, jejunum, and colon. Although arterial oxygen saturation improved, cardiac index and mean arterial pressure declined progressively; critically, intestinal perfusion collapsed suddenly when cardiac index fell to 37 ml/kg/min and MAP dropped to 52 mmHg (at PEEP 25 cmH₂O), followed by delayed gastrointestinal oxygen desaturation despite maintained systemic oxygenation. The authors identified no linear relationship between central perfusion pressure and splanchnic microvascular flow, suggesting that aggressive PEEP recruitment paradoxically compromises gut perfusion through reduced cardiac output rather than direct pressure transmission. For anaesthetists managing equine patients, this work underscores the importance of individualised PEEP titration with continuous haemodynamic monitoring; blindly pursuing maximal oxygenation without assessing systemic delivery may precipitate ischaemic gastrointestinal complications, particularly relevant given horses' post-operative colic risk.
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Practical Takeaways
- •During equine general anaesthesia, aggressive PEEP titration for oxygenation must be balanced against risk of compromising intestinal perfusion and potentially causing postoperative colic
- •Monitor cardiac output and blood pressure closely during mechanical ventilation; consider reducing PEEP if MAP drops below 55 mmHg or cardiac index below 40 ml/kg/min to preserve splanchnic perfusion
- •High airway pressures needed for equine lung recruitment may necessitate lower PEEP targets than would be used in other species to maintain acceptable peripheral tissue oxygenation
Key Findings
- •Lung recruitment via PEEP increased PaO2 from 201±58 mmHg to maximum 495±75 mmHg
- •Cardiac index and mean arterial blood pressure decreased linearly with increasing airway pressures
- •Critical threshold of CI 37±9 ml/kg/min and MAP 52±8 mmHg at PEEP 25 cmH2O triggered sudden intestinal perfusion decrease followed by delayed oxygenation decrease
- •Despite improved arterial oxygenation, high PEEP resulted in decreased gastrointestinal oxygenation due to reduced oxygen delivery from decreased cardiac index