An alpha2 agonist-ketamine combination is often used in veterinary anaesthesiology for anaesthetizing or immobilizing laboratory or domestic animals or animals reared in zoos. Depending on the dose ketamine has sedative, analgetic, psychomimetic, cataleptic and anaestetic effects. It stimulates blood circulation. It does not significantly alter the pattern of breathing. Alpha2 agonists include xylazine and recently medetomidine. They have a significant sympatholytic effect and lower noradrenaline level in the CNS by 75%. They reduce heart frequency by sympatholytic effect and stimulation of the vagus nerve and invoke a drop in blood pressure. Medetomidine has a hypnotic and anaesthetic effect in larger doses. Breathing is slightly influenced when clinical doses are used. Xylazine or medetomidine reduce the dose of ketamine by 40–60%, induce muscle relaxation and reduce the occurrence of psychomotor symptoms after ketamine. From the clinical point of view, breathing is not significantly influenced with this combination, cardiovascular stability is good. The possibility of using specific alpha2 antagonist agonists – atipamezol is the advantage. In the 1990s, a right-handed isomers of ketamine and medetomidine started to be used in the humaneanaesthesiology.Since 2000 dexmedetomidine has been registered as Precedex by Abbott Laboratories. Data on the use of an alfpha2 agonist – ketamine combination in humane anaesthesiology are rather scare. Lävenen and coll. (1995) gave dexmedetomidine in a pre-medication dose of 2.5 µg.kg-1 i. m. The intravenous ketamine dose could be reduced by 50%. At the same time the occurrence of psychomimetic symptoms was reduced too. According to our preliminary results with intravenous combination of midazolam with ketamine, dexmedetomidine at doses of 1 µg.kg-1 i. v. causes a marked reduction of the ketamin dosage and the occurrence of psychomimetic effects. The reduction of the ketamine dose during surgery was pronounced in the range of 60–70%. Advantages of the triple combination were very convincing, especially in dental surgery. Dexmedetomidine markedly reduces ketamine dosage and the subsequent reduction of the undesirable efects (esp.psychomimetic). It markedly potentiates hypnotic effect of ketamine and midazolam and analgetic effect of ketamin. Midazolammarkedly reduces the occurrence of psychomimetic effects after ketamine.When combined with dexmedetomidine, it markedly reduces the stimulatory effects of ketamine on the circulation. The triple combination has no clinically significant effects on respiration. Dexmedetomidine with midazolam protect against neurotoxic effects of ketamine and reduce the increased sympathetic tone caused by its administration. Psychomotor recovery after the triple combination is fast. There is a possibility to use specific antagonists flumazenil and atipamezol.The question remains whether the above mentioned triple combination could be used in a disastermedicine for patients with hypovolemia or in a haemorrhagic shock. In our preliminary experimental trials on rabbits we demonstrated that the medetomidine-ketamine combination during a haemorrhagic shock (central arterial pressure 40 mm Hg after a three hour period) had the highest survival rate. It was demonstrated in the tests on piglets that infusion of medetomidine with ketamine increases blood pressure in a haemorrhagic shock. However, further experiments are necessary to elucidate the role of medetomidine- ketamine combination in clinical anaesthesiology and emergency medicine.

        Key words: alpha2 agonist – ketamin – benzodiazepins