Use of dexmedetomidine repeated subcutaneous administration for balanced anaesthesia in horses

A balanced anaesthetic protocol is a common concept in modern veterinary anaesthesia and aims to maintain good intraoperative cardiopulmonary function. In horses, alpha-2-agonists produce sedation and analgesia and have been shown to reduce inhalational anaesthetic requirements when administered intravenously. Furthermore, these drugs can improve recovery quality. Preliminary investigations of subcutaneous dexmedetomidine administration in humans demonstrated a reduced haemodynamic impact if compared with the intravenous route suggesting that dexmedetomidine is adequately absorbed with both administration routes. The aim of the study was to compare two different dexmedetomidine (DEX) administration routes: intravenous constant rate infusion (CRI) versus repeated subcutaneous (SC) injections on cardiopulmonary function and recovery in anaesthetized horses.

No significant differences between groups in heart rate and systolic arterial pressure were detected. A significantly higher mean and diastolic arterial pressure were detected in the SC group at T25 (p = 0.04; p = 0.02), T75 (p = 0.02; p = 0.009), and T85 (p = 0.001; p = 0.005). In SC group there was a significantly lower dobutamine infusion rate (p = 0.03) and a significantly higher urinary output (p = 0.02). Moreover, recovery quality was higher (p = 0.01).

Cardiopulmonary effects in both groups were comparable and within clinical ranges with less dobutamine requirement in the subcutaneous group. Recovery was of better quality with fewer attempts in horses receiving subcutaneous dexmedetomidine. The present study suggests that intravenous constant rate infusion and subcutaneous repeated administration of dexmedetomidine at indicated dosage can be useful in balanced anaesthesia without any systemic or local adverse effects; moreover, in healthy horses undergoing general anaesthesia, repeated subcutaneous dexmedetomidine administration may be a suitable alternative if constant rate infusion is not feasible.