Propofol compared with propofoVguaiphenesin after detornidine premedication for equine surgery

Anaesthesia using propofol alone and in combination with guaiphenesin, after detomidine premedication, was evaluated for performance of minor surgical procedures (castration and tenotomy) in horses. Twelve male horses were premedicated with 0.015 mg/kg of detomidine intravenously (iv) and divided into two groups of six. One group of horses received 2 mg/kg of propofol iv and the other group received 0.5 mg/kg of propofol mixed with 100 mg/kg of a 7.5% solution of guaiphenesin in saline iv. Induction of anaesthesia was fast and smooth in both groups. All horses were easily intubated immediately afterwards but intubation was easier in the horses which received propofol and guaiphenesin. Heart rate fell by 20% in both groups after detomidine injection, stabilising between 45 and 53 beats/minute during anaesthesia with no difference between the groups. Respiratory depression developed after detomidine injection and was slightly intensified after induction of anaesthesia. Respiratory rate was significantly lower in the propofol group (14 ± 3 breaths/minute) than with propofol/guaiphenesin (19 ± 4 breaths/minute) at five minutes after induction. Anaesthesia induced respiratory acidosis in both groups and hypoxaemia also occurred, but once the horses stood up the arterial blood oxygen partial pressure returned to basal values. Surgical time ranged between 8 and 16 minutes and with the exception of one horse in the propofol/guaiphenesin group the horses did not show signs of pain or discomfort during surgery. Recovery to standing was fast and took 26 ± 2 minutes in the propofol and 29 ± 5 minutes in the propofol/ guaiphenesin group. Most horses stood up at the first attempt with minimal ataxia. These two anaesthetic techniques appear to be useful for minor surgical procedures performed within 16 minutes of induction of anaesthesia.