Hematological and Physiological Effects of Ketamine with and without Xylazine in Dogs

Ketamine hydrochloride is a dissociative anesthetic of the cyclohexylamine group used for chemical restraint and for the induction and maintenance of anesthesia in a number of species. Unlike many anesthetics, ketamine usually stimulates cardiovascular function in normal animals, causing increase in heart rate (HR) and mean arterial pressure (MAP). The use of ketamine as a sole anesthetic has been limited by muscle hypertonicity and myoclonus, violent recovery and occasional occurrence of convulsions [1]. Ketamine is combined with an alpha-2-agonist (e.g. xylazine), a benzodiazepine (e.g. diazepam) or a phenothiazine tranquillizer (e.g. acepromazine) to enhance muscle relaxation, analgesia, to prevent seizures/convulsions and prolong the duration of anesthetic effect. It is associated with a rapid onset, good to excellent sedation of one to two hours duration, excellent analgesia and smooth recovery. The analgesia and sedation are due to central nervous system depression and the muscle relaxation is due to the central inhibition of intraneural transmission [2]. Ketamine is poor in visceral analgesia. However, it can be used in combination with xylazine or diazepam to provide good visceral analgesia in case of abdominal surgery (including ovariohysterectomy) and thoracic surgery. Pain is an unpleasant sensory or emotional experience most commonly associated with potential tissue damage. The sensation of pain is a consequence of the activation of specialized receptors and neurological pathways after such pain stimuli [3,4]. Xylazine, an alpha-2 agonist used in animal experiments, stimulates alpha-2 adrenergic receptor in cerebral presynaptic nerve ends, inhibits release of catecholamines and dopamine resulting in analgesic and sedative eff ects, and hinders nerve conduction in the central nervous system leading to relaxation of striated muscles. Xylazine is usually used in combination with ketamine during anesthetic applications [5].