Effects of five hours of constant 1.2 MAC halothane in sternally recumbent, spontaneously breathing horses.

The research article discusses the effects of the anesthetic halothane on horses’ circulatory and respiratory systems over a five-hour period. Its major findings indicate that while few significant changes occurred over the test duration, the use of halothane caused a reduction in total peripheral resistance and arterial blood pressure, and increased heart rate in horses.

Research Setup

• The study involved eight healthy horses who breathed naturally without any additional medication and were positioned in sternal recumbency.
• The horses were given a constant 1.06 percent of alveolar halothane in oxygen, a common general anesthetic used in veterinary practice, for five hours.

Effects on the Circulatory System

• The total peripheral resistance was observed to be 15 percent lower after two hours of halothane administration than after 30 minutes. This reduction accounted for a significant 10 percent decrease in the mean carotid arterial blood pressure.
• By the end of the five-hour period, the reduction in resistance and arterial blood pressure was seen to be 20 and 25 percent, respectively.
• The horses’ heart rates increased progressively over the five-hour period, becoming significant with a 15 percent increase at the end of the test. However, these changes in heart rate did not lead to alterations in cardiac output.

Effects on the Respiratory System

• No major time-dependent changes were observed in the partial pressures of oxygen (PaO2) or carbon dioxide (PaCO2) in the blood.
• This suggests that the five-hour administration of halothane did not adversely affect the horses’ ability to respire or exchange gases.

Post-Anesthetic Effects

• Three of the four horses that recovered from anesthesia showed significantly elevated levels of serum creatine kinase. This enzyme is typically associated with muscle damage.
• The same horses also exhibited clinical signs of severe post-anaesthetic myopathy, a condition defined by muscle weakness and damage often associated with the use of certain anesthetic drugs.