MEDETOMIDINE-MIDAZOLAM SEDATION IN SHEEP

Seven sheep were sedated 3 times: with medetomidine (15 mu g kg(-1)), with midazolam (0.1 mg kg(-1)) and with a combination of the drugs. Al l drugs were administered intravenously. Heart and respiratory rates w ere measured. Arterial blood samples were collected, and PaO2, PaCO2, pH, haemoglobin concentration and saturation, and base excess were det ermined. Systolic and mean arterial pressures were recorded before and after the treatment with medetomidine-midazolam. Midazolam increased the time of recumbency induced by medetomidine. After administration o f midazolam alone, 4 of the 7 sheep were sedated and the other 3 were excited. Heart rate decreased after both medetomidine and medetomidine -midazolam. One sheep suffered a cardiac arrest after medetomidine-mid azolam injection, and it required resuscitation. PaO2 and haemoglobin oxygen saturation decreased after medetomidine, and medetomidine-midaz olam caused a marked hypoxaemia. PaCO2 increased after medetomidine, b oth alone and combined with midazolam, but arterial pH was within the reference values after all drug administrations. Systolic and mean art erial pressures decreased after medetomidine-midazolam. This study ind icates that though in sheep midazolam potentiates the sedative effect of medetomidine, the combination of medetomidine and midazolam also re duces the in PaO2 and haemoglobin oxygen saturation more than medetomi dine alone. The results indicate that a medetomidine-midazolam combina tion is unsafe for sheep at the doses studied.