The effects of pulse-delivered inhaled nitric oxide on arterial oxygenation, ventilation-perfusion distribution and plasma endothelin-1 concentration in laterally recumbent isoflurane-anaesthetized horses.

摘要

Objectives: Anaesthetized horses commonly become hypoxaemic due to ventilation/perfusion (V_A/Q) mismatch and increased pulmonary shunt fraction (Q_s/Q_t). Pulse-delivered inhaled nitric oxide may improve oxygenation but may increase plasma concentration of the potent vasoconstrictor, endothelin-1 (ET-1). Objectives: (Study 1) compare arterial oxygen concentration (PaO₂) and saturation (SaO₂), calculated Q_s/Q_t and ET-1 concentration; and (Study 2) assess V_A/Q matching and measured Q_s/Q_t in isoflurane-anaesthetized horses in left lateral recumbency receiving pulse-delivered inhaled nitric oxide (PiNO group) or inhalant gas only (C group). Study design: Prospective research trial. Animals: Ten Healthy adult Standardbred horses. Two horses were anaesthestized in both groups in a random cross-over design with >4 weeks between studies. Methods: (Study 1) Cardiopulmonary data including PaO₂, SaO₂, Q_s/Q_t and ET-1 concentration were measured or calculated prior to and at various points during PiNO administration in 6PiNO and 6C horses. Two-way repeated measures ANOVA with Bonferroni significant difference test was p<0.05 considered significant. (Study 2) V_A/Q matching and Q_s/Q_t were determined using the multiple inert gas elimination technique in 3 horses. Data were collected after 60 minutes of anaesthesia without PiNO (baseline) and 15 minutes after PiNO was pulsed during the first 30%, and then the first 60%, of inspiration. Data were descriptive only. Results: (Study 1) Pao₂ and SaO₂ were higher and calculated Q_s/Q_t was lower in the PiNO group than the C group at most time points. ET-1 was not different over time or between groups. (Study 2) Va/Q matching and measured Q_s/Q_t were improved from baseline in all horses but PiNO60% provided no improvement when compared to PiNO30%. Conclusions and Clinical Relevance: PiNO delivered in the initial portion of the inspiration effectively relieves hypoxaemia in anaesthetized horses by improving VA/Q matching and decreasing Q_s/Q~_t without affecting ET-1.