Comparison of Medetomidine and Dexmedetomidine as Premedication in Isoflurane Anaesthesia for Orthopaedic Surgery in Domestic Sheep

Abstract

The objective of the present study was to determine the potency of dexmedetomidine in relation to medetomidine in sheep undergoing orthopaedic surgery by comparing the anaesthetic requirements and cardiovascular changes at a dose relationship that represented equipotency in vitro. Twenty-four non-pregnant, female sheep were used. The study was carried out as a blind, randomized, experimental trial. Group 1 received 5 micrograms/kg bodyweight (BW) dexmedetomidine and group 2 received 10 micrograms/kg BW medetomidine intravenously 5 min prior to induction of anaesthesia. Anaesthesia was induced with ketamine (2.0 mg/kg BW intravenously) and maintained with isoflurane in 100% oxygen. End expired anaesthetic concentration (FEIso), end expired carbon dioxide concentration (FECO2), respiratory frequency (fR), direct arterial blood pressures, heart rates (HR) and arterial blood gases were monitored. Data were averaged over time and tested for differences between groups by independent t-tests, and analysis of variance for repeated measures. Average FEIso concentrations required to maintain a surgical plane of anaesthesia were not different between groups (1: 1.02 +/- 0.04%; 2: 0.99 +/- 0.07%). There was no difference in HR, arterial blood pressures, fR, FECO2 and arterial blood gases between groups. Average mean PaO2 were 279.54 +/- 113.37 mmHg and 220.21 +/- 102.15 mmHg with individual minimum values of 27.2 mmHg and 58.5 mmHg in groups 1 and 2, respectively. In conclusion, intravenous dexmedetomidine at 5 micrograms/kg BW and medetomidine at 10 micrograms/kg BW have the same effects on isoflurane requirements and cardiopulmonary parameters in sheep, indicating an equipotent dose relationship. Both preparations induced moderate to severe hypoxaemia in individual sheep.

Behavioral and cardiopulmonary effects of dexmedetomidine alone and in combination with butorphanol, methadone, morphine or tramadol in conscious sheep

“…Dexmedetomidine has been used in sheep as premedication prior to general anesthesia (Kästner et al. , b, ; Kästner ; Granados et al. ; Funes et al.…”

“…; Kästner et al. ; Kästner ). Congestion and redistribution of blood flow have been suggested as the cause of impaired oxygenation following the administration of dexmedetomidine to healthy anesthetized sheep.…”

“…In sheep, a 2 -agonists are widely used for provision of analgesia and sedation (K€ astner 2006). However, arterial hypoxemia and pulmonary edema have been reported in certain breeds of sheep following the administration of all a 2agonists, including dexmedetomidine (Celly et al 1997;K€ astner et al 2001b;K€ astner 2006). Congestion and redistribution of blood flow have been suggested as the cause of impaired oxygenation following the administration of dexmedetomidine to healthy anesthetized sheep.…”

A comparison of medetomidine and its active enantiomer dexmedetomidine when administered with ketamine in mice

“…The statistical analyses of related previous work have relied heavily on repeated measures analysis of variance (ANOVA) [13,14,19,25-27,43]. While these tests account for a degree of dependence between data points, the mixed effects modeling approach we utilised is more flexible and robust than more common analyses.…”

A2-agonists in sheep: a review

“…More recent reports describe arterial hypoxaemia and pulmonary oedema in sheep after the use of the newer α 2 ‐agonists detomidine, medetomidine, dexmedetomidine and romifidine (Celly et al. 1997b; Kästner et al. 2001b).…”