Minimal alveolar concentration of desflurane in combination with an infusion of medetomidine for the anaesthesia of ponies

Abstract

The minimum alveolar concentration of desflurane when combined with a continuous infusion of medetomidine at 3.5 microg/kg/hour was measured in seven ponies. Anaesthesia was induced with medetomidine (7 microg/kg intravenously) followed by ketamine (2 mg/kg intravenously) and maintained with desflurane in oxygen. The infusion of medetomidine was started 20 minutes after the induction of anaesthesia. The electrical test stimulus was applied at the coronary band (50 V, 10 ms bursts at 5 Hz for one minute), and heart rates and rhythms, arterial blood pressures, and arterial blood gas tensions were measured at intervals, just before the application of the stimulus. The mean (sd) minimum alveolar concentration of desflurane was 5.3 (1.04) per cent (range 3.2 to 6.4 per cent), 28 per cent less than the previously published value for desflurane alone after the induction of anaesthesia with xylazine and ketamine. The cardiopulmonary parameters remained stable throughout the period of anaesthesia. The mean (sd) time taken by the ponies to stand after the administration of desflurane ceased was 16.5 (6.17) (range 5.8 to 26) minutes, and the quality of recovery was good or excellent. However, one pony died shortly after standing; a postmortem examination revealed that it had chronic left atrial dilatation.

Clinical assessment of anesthesia with isoflurane and medetomidine in 300 equidae

“…Different authors showed a reduction of the minimal alveolar concentration (MAC) of various inhalational agents by administration of a constant rate infusion (CRI) of medetomidine, ketamine or a combination of different drugs (Bettschart-Wolfensberger et al 2001, Muir and Sams 1992, Neges et al 2003. Some regimes were investigated in experimental animals (Bettschart-Wolfensberger et al 2001, Dzikiti et al 2003, Kushiro et al 2005, Muir and Sams 1992, some in clinical studies with caseloads of 12 to 40 horses (Spadavecchia et al 2002, Yamashita et al 2002. One study including 69 clinical patients compared isoflurane-lidocaine versus isoflurane-medetomidine balanced anesthesia in a randomized, prospective, blinded manner (Ringer et al 2005).…”

“…Medetomidine possesses an inhalational agent sparing effect (Bettschart-Wolfensberger et al 2001, Neges et al 2003. If less inhalational anesthetic can be used, pulmonary depression caused by the volatile agent is reduced.…”

Changes in minimal alveolar concentration of isoflurane following treatment with medetomidine and tiletamine/zolazepam, epidural morphine or systemic buprenorphine in pigs

“…Also, in other animal species it has been reported that analgesics administered as anaesthetics adjuncts decrease the requirement of volatile anaesthetics and thus reduce the dose-dependent cardiopulmonary depression (Ewing et al 1993, Bettschart-Wolfensberger et al 2001, Greene et al 2003. Medetomidine is an a2-adrenoceptor agonist that has been reported to provide potent analgesia, muscle relaxation and anxiolysis in dogs (Thurmon et al 1994), cats (Smith et al 2004), ponies (Bettschart-Wolfensberger et al 2001) and pigs (Nishimura et al 1993, Tendillo et al 1996. Tiletamine/zolazepam are available in a drug combination of 1:1 for intramuscular (IM) or intravenous (IV) administration and produces sedation and anaesthesia in many species e.g.…”

Effects of Medetomidine Constant Rate Infusion on Sevoflurane Requirement, Cardiopulmonary Function, and Recovery Quality in Thoroughbred Racehorses Undergoing Arthroscopic Surgery

“…On the other hand, others reported that medetomidine CRI reduced the MAC of desflurane by 28% [16] and that dexmedetomidine CRI reduced the MAC of sevoflurane by 53% [22] in experimental ponies. These results indicate that experimental MAC reduction study is desirable to detect correct anesthetic-sparing effects.…”

“…It was reported that medetomidine CRI reduced the minimum alveolar concentration (MAC) of desflurane by 28% in experimental ponies [16]. Others reported that isoflurane anesthesia in combination with medetomidine CRI resulted in improved cardiopulmonary function, analgesia, and muscle relaxation [13,15].…”