Systemic effects and clinical application of dexmedetomidine

Dexmedetomidine is a most potent α-2 adrenergic selective agonist. It is one of the components of the racemic mixture of two enantiomers of medetomidine. It has a selectivity ratio of 1620/1(α 2/ α1), which is 5–10 times higher than that for detomidine (260/1) and xylazine (160/1. Dexmedetomidine produces consistent sedation, anxiolysis and muscle relaxation, which makes it a popular sedative agent in veterinary medicine. In veterinary practice, it is used for premedication and as an adjunct to general anaesthesia in several species. Similar to other alpha-2 agonists it exerts its effect through the action on alpha-2 adrenergic receptors. The sedative and anxiolytic effects of α-2 agonists are mediated by agonism of supraspinal autoreceptors situated in the pons, whereas analgesic effects are mediated by agonism of heteroreceptors located in the dorsal horn of the spinal cord. Dexmedetomidine causes a dose-dependent redistribution of blood flow and preserves blood flow to the most vital organs at the expense of organs like skin and pancreases and this distribution of blood flow is not affected by the type of anaesthesia. The pattern of cardiovascular changes may be affected by the dose used and the type of anaesthetic combined with dexmedetomidine. Most anaesthetic drugs, such as propofol, thiopental, isoflurane and halothane have cardiovascular and respiratory side effects that are dose-dependent. Dexmedetomidine is a good anaesthetic adjuvant for general anaesthesia which reduces intra-operative isoflurane consumption provides analgesic-sparing effect without affecting postoperative recovery profile and improved cardiovascular stability and contributes to the provision of balanced anaesthesia.