Читать книгу Farm Animal Anesthesia - Группа авторов - Страница 34

Medetomidine induced dose‐dependent sedation and analgesia in sheep at doses of 0.001–0.007 mg/kg IV, with the level of analgesia produced by 0.005 mg/kg comparable to that of 0.015 mg/kg of fentanyl [93]. At 0.04 mg/kg IM, medetomidine induced 30–45 minutes of good analgesia and marked muscle relaxation and 58 minutes of recumbency. Full recovery usually occurred within 1½–2 hours after regaining the righting reflex [94]. When used as a preanesthetic administered 30 minutes prior to induction with propofol and maintenance with isoflurane, medetomidine (0.005 or 0.01 mg/kg IM) decreased heart rate and respiratory rate. Mean arterial blood pressure values were significantly higher following a high dose (0.01 mg/kg IM) as compared to those without preanesthetic medetomidine or those administered at a lower dose (0.005 mg/kg IM). In general, the administration of medetomidine reduced the dose requirement of propofol for induction and isoflurane for maintenance of anesthesia during surgery [95]. In sheep breathing room air that are anesthetized with medetomidine (0.02 mg/kg IV) and ketamine (2 mg/kg IV), PaO₂, arterial pH, and arterial O₂ saturation (SaO₂) decreased and PaCO₂ increased significantly. Supplementation of 100% O₂ improved PaO₂ and SaO₂ [96]. Similar to all other α₂ agonist drugs, medetomidine (0.01 mg/kg IV) caused characteristic hypoxemia in sheep breathing room air during sedation [82].

When given to produce lumbosacral analgesia in goats, medetomidine at doses of 0.01, 0.02, and 0.03 mg/kg diluted in sterile water to a total volume of 5 ml produced satisfactory analgesia in the perineum and flank regions, and the analgesia extended to the thorax, forelimbs, neck, and head for a period of at least 3 hours. Ten goats receiving 0.02 mg/kg underwent laparotomy surgery; adequate analgesia was apparent in all tissue layers (from skin to external and internal oblique muscles and transverse muscles). All 10 goats recovered uneventfully from surgery. Lateral recumbency and characteristic side effects of other α₂ agonists were observed during the study, particularly with higher doses (0.02 and 0.03 mg/kg). One goat receiving 0.01 mg/kg was paralyzed following lumbosacral injection and was humanely euthanized. Because of the caudal extension of the spinal cord into the cauda equina in goats, it was speculated that the trauma to the conus medullaris and/or cauda equina resulting from struggling of the animal at the time of spinal needle insertion was responsible for the paralysis observed in this goat [97].

IM administration of medetomidine (0.01–0.03 mg/kg IM) has also been used in llamas. Sternal recumbency (5.3 ± 4.7 minutes) and mild to moderate sedation (37.3 ± 9.5 minutes) without analgesia were observed in two of three llamas receiving 0.01 mg/kg of the drug. All llamas receiving 0.02 mg/kg assumed sternal recumbency but with only slightly more profound sedation (58 ± 12.1 minutes) and analgesia (30 minutes) than that of 0.01 mg/kg. When the dose was increased to 0.03 mg/kg, medetomidine induced immobilization (91.5 ± 24.7 minutes) with profound analgesia (61.7 ± 2.9 minutes) and muscle relaxation. The only side effect observed during the period of immobilization was a significant decrease in heart rate. Atipamezole (0.125 mg/kg IM) effectively reversed the effect of medetomidine (0.03 mg/kg IM), and standing recovery occurred within 5.8 ± 3.3 minutes [98].