Nasal and tracheobronchial nitric oxide production and its influence on oxygenation in horses undergoing total intravenous anaesthesia.
Authors: Wilkens Henriette L, Neudeck Stephan, Kästner Sabine B R
Journal: BMC veterinary research
Summary
# Editorial Summary: Endotracheal Intubation and Nitric Oxide in Equine Anaesthesia Nitric oxide produced in the nasopharynx acts as an endogenous pulmonary vasodilator, optimising lung perfusion and gas exchange in spontaneously breathing animals—a physiological advantage potentially lost when endotracheal intubation bypasses the upper airway. This study compared nasal and tracheal nitric oxide concentrations alongside oxygenation parameters in six anaesthetised horses randomly assigned to intubated or non-intubated groups, maintaining both under total intravenous anaesthesia with spontaneous breathing of room air and measuring blood gases, haemodynamics, and nitric oxide levels at regular intervals throughout a 100-minute period. Whilst intubation significantly reduced both nasal and tracheal endogenous nitric oxide (from ~17 ppb and ~19 ppb to ~8 ppb and ~13 ppb respectively), this reduction produced only a modest increase in alveolar-arterial oxygen gradient (6.1 versus 4.9 kPa) with no clinically meaningful differences in arterial oxygen tension, oxygen saturation, oxygen extraction ratio, or other oxygenation indices between groups. For practitioners managing anaesthetised horses breathing room air, these findings suggest endotracheal intubation's interruption of nasopharyngeal nitric oxide production has negligible practical impact on gas exchange and oxygenation, though the long-term effects during prolonged procedures or compromised respiratory function remain unclear and warrant further investigation.
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Practical Takeaways
- •Endotracheal intubation during equine general anaesthesia bypasses nasopharyngeal nitric oxide production, but this does not clinically compromise oxygenation in horses breathing room air
- •The negligible clinical impact of reduced NO on gas exchange suggests intubation decisions can be made based on airway management and anaesthetic protocol needs rather than concern about NO-related hypoxaemia
- •Monitor standard oxygenation indices rather than NO levels; the physiological compensatory mechanisms appear adequate in anaesthetised equine patients
Key Findings
- •Endotracheal intubation significantly reduced both nasal (8.0 ppb) and tracheal (13.0 ppb) nitric oxide concentrations compared to non-intubated horses (16.9 and 18.5 ppb respectively)
- •Intubated horses had significantly higher alveolar-arterial oxygen gradient P(A-a)O2 (6.1 kPa) versus non-intubated (4.9 kPa), indicating mild impairment in oxygenation efficiency
- •Despite reduced NO production and increased oxygen gradient, all other oxygenation parameters (PO2, PCO2, saturation, oxygen extraction ratio, shunt fraction) were not significantly different between groups in room air breathing horses