Evaluation of 25%, 50%, and 67% nitrous oxide with halothane-oxygen for general anesthesia in horses.

This research studied how different concentrations of nitrous oxide affect horses when it is used alongside halothane and oxygen for general anesthesia, and found that a concentration above 25% did not provide significant benefits and could potentially be harmful.

Research Methodology

• The researchers administered a variety of nitrous oxide concentrations (25%, 50%, and 67%) to 12 horses under general anesthesia with halothane and oxygen.
• The impact of these different nitrous oxide concentrations was examined in several aspects related to the horse’s physiological condition during anesthesia. This included their heart rate, blood pressure (systolic, diastolic, mean), arterial pH, partial pressure of carbon dioxide (PaCO2), plasma bicarbonate values, and partial pressure of oxygen (PaO2).

Research Findings

• The study found that adding nitrous oxide to the anesthetic mix did not significantly change the horse’s physiological parameters, with heart rate, blood pressures, pH levels, PaCO2, or bicarbonate values remaining consistent.
• However, the study discovered a significant linear reduction in PaO2 values (oxygen levels in the blood) that corresponded with the the concentrations of nitrous oxide and oxygen. This indicates that as the concentration of nitrous oxide increased, the ability of the blood to carry oxygen decreased.
• The researchers also determined that the amount of halothane needed to maintain surgical anesthesia was reduced when nitrous oxide was used. Interestingly, this effect was consistent regardless of the concentration of nitrous oxide used.
• Additionally, the study concluded that nitrous oxide concentrations higher than 25% did not lead to any further reductions in the requirement for halothane. Instead, these higher concentrations were associated with PaO2 values that could pose health risks to the horse.

Conclusion

• The researchers concluded that while nitrous oxide can effectively reduce the amount of halothane necessary for anesthesia, increasing the concentration of nitrous oxide beyond 25% does not yield additional advantages. It could, however, potentially endanger the horse by reducing the oxygen levels in its blood to critical levels. Therefore, it is advisable to use nitrous oxide with caution and adhere to recommended concentration limits when using it for equine anesthesia.