Clinical use of atracurium in horses undergoing ophthalmic surgery.

The study examines the use of atracurium, a drug given during anaesthesia, in horses that are undergoing eye surgery. The study included 16 horses and took place over a two-years period at the University of Liverpool.

Methods

• The study involved one stallion, eight geldings and seven mares. Their median weight was 520 kg, and they were between 4 and 25 years old.
• The anaesthesia started with the administration of 0.1mg/kg of atracurium intravenously before the surgery commenced. The anaesthesia was then maintained with halothane in 02 delivered by a large-animal ventilator.
• Throughout the surgery, the anaesthetist monitored the horses’ neuromuscular blockade by way of their response to train-of-four (TOF) stimulation of the peroneal nerve.
• The duration of action was recorded from the time all four twitches ceased until two twitches returned. If two twitches were observed, or it was necessary to maintain central eye position, maintenance doses of atracurium (0.02 mg kg-1) were administered
• At the end of surgery, the horses’ neuromuscular blockade was antagonized with edrophonium (0.1 mg kg-1) when two twitches were once again observed. Mechanical ventilation was stopped upon the administration of edrophonium.

Results

• The average duration of effect for the initial dose of atracurium was just over 27 minutes. Most horses required one or two additional doses, which had smaller durations of effect.
• Following the administration of edrophonium, all twitches typically returned within 3 minutes.
• The time it took for spontaneous respiration to return after the administration of edrophonium was roughly 4.5 minutes.
• The recoveries were assessed as satisfactory to excellent in all cases. However, in two horses, eye and eyelid movement was observed even without a visible response to peroneal nerve stimulation.
• The response to atracurium varied between horses but was not cumulative. This supports previous findings that horse facial muscles are more resistant to the effects of atracurium than lower limb muscles.

Conclusion

The results suggest that atracurium can be used effectively and safely as an anaesthetic for horses undergoing eye surgery. Some horses might require additional doses during the surgery, and recovery times post anaesthesia were satisfactory to excellent. Given the findings, the researchers recommend the use of atracurium anaesthetic techniques in equine ophthalmic surgeries.