Effects of pulsed inhaled nitric oxide on arterial oxygenation during mechanical ventilation in anaesthetised horses undergoing elective arthroscopy or emergency colic surgery.
Authors: Wiklund M, Kellgren M, Wulcan S, Grubb T, Nyman G
Journal: Equine veterinary journal
Summary
# Editorial Summary: Pulsed Inhaled Nitric Oxide During Mechanical Ventilation in Anaesthetised Horses Hypoxaemia during equine anaesthesia remains a significant challenge, particularly when hypoventilation necessitates mechanical support; whilst inhaled nitric oxide (NO) has shown promise in spontaneously breathing horses, its efficacy during positive pressure ventilation was unclear. Wiklund and colleagues conducted a prospective clinical trial across 80 horses—50 undergoing arthroscopy and 30 presenting for colic surgery—randomly assigning every second animal to receive pulsed NO delivered at the endotracheal tube during inspiration, with arterial blood gas analysis performed at baseline and end of anaesthesia. Arterial oxygen tension (PaO₂) improved markedly in NO-treated groups, rising from 13.6 to 24.2 kPa in arthroscopy cases (P = 0.005) and from 7.7 to 15.5 kPa in colic cases (P = 0.007), whilst functional shunt decreased by 6–11 percentage points; control animals receiving mechanical ventilation alone showed no improvement in either parameter. These findings suggest that combining mechanical ventilation with pulsed NO optimises pulmonary gas exchange through simultaneous reductions in intrapulmonary shunt and enhanced alveolar ventilation—a mechanistic advantage worth considering in clinical protocols, particularly for lengthy procedures or where baseline oxygenation is compromised, though the authors acknowledge that oxygen delivery cannot be fully assessed without concurrent cardiac output measurement.
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Practical Takeaways
- •PiNO significantly improves oxygenation during general anaesthesia in mechanically ventilated horses undergoing arthroscopy and colic surgery, potentially reducing perioperative hypoxaemia complications
- •PiNO delivery is practical during routine anaesthesia (pulsed delivery at endotracheal tube) and may be particularly beneficial in emergency colic cases where baseline oxygenation is compromised
- •For anaesthetists managing horses at risk of hypoxaemia, adding PiNO to mechanical ventilation protocols should be considered as an evidence-based intervention to improve arterial oxygen tension and reduce pathological shunting
Key Findings
- •Pulsed inhaled nitric oxide (PiNO) increased arterial oxygen tension (PaO2) in arthroscopy horses from 13.6 kPa to 24.2 kPa (P=0.005) and in colic surgery horses from 7.7 kPa to 15.5 kPa (P=0.007)
- •PiNO reduced functional shunt (F-shunt) by 6% in arthroscopy group (P=0.005) and 11% in colic surgery group (P=0.04)
- •Control groups receiving mechanical ventilation alone showed no improvement in PaO2 or F-shunt from baseline to end of anaesthesia
- •Combination of mechanical ventilation and PiNO improved pulmonary gas exchange through simultaneous decrease in shunt and improved alveolar ventilation