Clinical evaluation of an infusion of xylazine, guaifenesin and ketamine for maintenance of anaesthesia in horses.

General anaesthesia was maintained in 40 horses by the continuous intravenous infusion of a mixture of 500 ml 10% guaifenesin solution, 1 g ketamine and 500 mg xylazine. The median duration of infusion was 65 mins (interquartile range 51-95 mins). Anaesthesia was characterised by active palpebral reflexes, variable degrees of nystagmus and occasional swallowing. Swallowing was considered to be undesirable in horses undergoing laryngeal surgery, but the infusion produced satisfactory conditions for all other surgical procedures performed. Arterial blood pressure was well maintained in all cases (median mean arterial blood pressure = 85 mmHg after 30 mins anaesthesia). Heart rate and PaCO2 were significantly lower, whilst PaO2 was significantly higher in the infusion group than in a group of paired control horses which were anaesthetised with halothane. Recovery from anaesthesia was good (Grades 1-2) in 33 horses. Median times to sternal recumbency and to standing were 24 and 38 mins respectively. The infusion caused a significant fall in packed cell volume, haemoglobin concentration and red blood cell count (P < 0.01) and a significant rise in plasma glucose concentration (P < 0.01). These variables returned to pre-infusion values within 24 h.