Effects of inhaled nitric oxide 10 ppm in spontaneously breathing horses anaesthetized with halothane.

The study explores the effects of inhaled nitric oxide (a selective pulmonary vasodilator) on the pulmonary hemodynamics and venous admixture in horses under halothane anesthesia. Despite theoretical benefits, this study indicates that inhaled nitric oxide does not significantly change pulmonary dynamics or alters oxygenation in healthy horses under general anesthesia with spontaneous ventilation.

Research Design and Methodology

• The study was carried out on seven adult horses, each examined twice in a randomized sequence.
• The horses were premedicated with a substance called romifidine at a specific dosage prior to the induction of anesthesia using ketamine. The anesthesia was maintained with a sedative halothane combined with oxygen.
• Each horse after 65 minutes, had nitric oxide added to the inspired gas or the anesthesia was continued with just halothane and oxygen. This was done to create two separate groups of procedures- HA (Halothane alone) and HA + NO (Halothane with Nitric Oxide).
• Various parameters related to heart function, pulmonary function and gas tensions i.e. cardiac output, minute ventilation, arterial and mixed venous oxygen and carbon dioxide tensions, and mean pulmonary and carotid arterial pressures were measured for 100 minutes.
• Additional parameters like shunt fraction and pulmonary and systemic vascular resistances were also calculated to determine any resultant changes.

Results

• The study found no significant difference between the two groups in terms of Shunt Fraction (SF) and Mean Pulmonary Artery Pressure (PPA mean) after 65 and 85 minutes of general anaesthesia.
• No significant effects of time or nitric oxide inhalation were noticed on any other variable of interest.
• However, a substantial correlation was observed between the calculated shunt fraction 65 minutes after the induction of anesthesia and the body weight of the horse.

Conclusion

• Given these findings, the study concludes that inhalation of nitric oxide does not significantly affect shunt fraction or pulmonary artery pressure. Similarly, it does not show any significant impact on any other variables in horses under halothane anesthesia.
• These results indicate that despite nitric oxide being a known selective pulmonary vasodilator, it does not demonstrate significant changes in pulmonary dynamics or oxygenation in healthy horses under halothane anesthesia with spontaneous ventilation.