MEDETOMIDINE, AN ALPHA(2)-AGONIST, ALLEVIATES POSTTHORACOTOMY PAIN INDOGS

Twelve laboratory beagles underwent a routine left thoracotomy to inse rt permanent instrumentation. Every second dog was given 10 mu g/kg of medetomidine, an alpha(2)-agonist sedative. The rest of the animals w ere treated with 20 mu g/kg of buprenorphine, an opioid agonist-antago nist, which is regularly used to treat postoperative pain in laborator y animals. The drugs were given at the end of operation (0) and 4, 8, 20, and 24 h postoperatively. Blood samples for catecholamines (adrena line and noradrenaline) and blood gases (pCO(2) and pO(2)) and pH were drawn immediately before any drug administration, and 30 min later. A t the same time points, the pain level was subjectively evaluated usin g a pain score, and heart rate and rectal temperature were measured. A drenaline and noradrenaline concentrations were lower in the medetomid ine group than in the buprenorphine group. Accordingly, it was conclud ed that medetomidine had better analgesic effect than buprenorphine in the treated animals. This result was supported by subjective evaluati on of the severity of pain, even though subjective evaluation is not c onsidered very reliable in the present kind of open studies. pO(2) was lower in the buprenorphine group than in the medetomidine group after the first injection of the analgesics. pCO(2) and pH were similar in both of the groups. Medetomidine decreased heart rate after every inje ction, this fall and subsequent rise might be avoided by a lower dose regime. Buprenorphine did not effect heart rate. Rectal temperature di d not differ in either group. It was concluded that medetomidine, and other alpha(2)-agonists, possess some potential in postoperative pain alleviation.