Effects of atracurium administered by continuous intravenous infusion in halothane-anesthetized horses.

This research examines the effects of administering atracurium, a muscle relaxant, intravenously over two hours to halothane-anesthetized horses, and observes how it influences the recovery speed and quality post-anesthesia.

Objective of the Research

The aim of the study was to determine the impact of the drug atracurium, delivered through intravenous infusion, on anesthetized horses. Specifically, the researchers wanted to:

• Investigate how much atracurium was needed to maintain muscle relaxation over a period of two hours.
• Monitor the amount of time it took for the horses’ muscle strength to recover.
• Observe how long it took for the horses to stand after discontinuation of anesthesia.

Methodology of the Study

The study was conducted on seven adult horses that were healthy. The researchers used a solution of atracurium (0.4 mg/ml) diluted in isotonic NaCl and administered it intravenously. Observations were focused on:

• Train-of-four hoof-twitch response: this was used as a measure of how effectively the drug induced muscle relaxation in the horses.
• Recovery times: both for muscle strength (from 10% to 75% of baseline strength) and the time it took for the horse to get back up after halothane anesthesia was stopped.

Results of the Study

The results showed that atracurium maintained the hoof-twitch response reduction between 95-to-99%. To maintain this level of relaxation, an average of 0.17 +/- 0.01 mg of atracurium per kg body weight per hour was needed.

Out of all the horses, horse number 5, a mare in estrus required much higher atracurium dosage (0.49 mg/kg/hr), to achieve the same muscle relaxation. The recovery times varied among the horses, with an average of around 19.8 +/- 2.5 minutes to recover muscle strength from 10% to 75% of baseline strength. The average time it took the horses to stand after halothane was discontinued was 86 +/- 14 minutes.

Interestingly, mare number 5 took the longest to recover (165 minutes), but her recovery was marked by a single, strong, smooth effort to stand, indicating effective recovery.

Conclusion of Research

Overall, the results indicate that atracurium can successfully maintain muscle relaxation in horses over a 2-hour period when administered through an IV infusion. However, recovery times can vary greatly depending on individual factors such as hormonal state (like mare number 5 being in estrus). The research could potentially be used to guide the use of atracurium and anesthesia in veterinary practice for horses.