Romifidine or medetomidine premedication before propofol-sevoflurane anaesthesia in dogs.

Romifidine is an a2-adrenergic agonist sedative used in smallanimals, with similar sedative actions to other drugs of itspharmacological group (England et al., 1996a). Romifidineinduces dose-dependent cardiovascular changes in dogs andthese changes are similar to those observed with other a2-adrenergic agonists: a marked decrease in heart rate (HR),atrioventricular blocks, biphasic effect of arterial blood pressureand reduction in cardiac output have been described (Englandet al., 1996a; England & Alibhai, 1997; Lemke, 1999; Pypendop& Verstegen, 2001; Sinclair et al., 2003).Propofol is an alternative to thiopentone for induction ofgeneral anaesthesia in dogs sedated with romifidine (Redondoet al., 2000), and has been shown to be effective in combinationwith romifidine and halothane anaesthesia in dogs (Redondoet al., 1999).Sevoflurane is a volatile anaesthetic that provides anaesthesiawith rapid and smooth induction and recovery (Clarke, 1999).Sevoflurane has a variable effect on HR, causes systemicvasodilation and produces dose-dependent decreases in meanarterial pressure (MAP), total peripheral resistance and cardiacoutput (Mutoh et al., 1997). Sevoflurane causes dose-relatedrespiratory depression characterized by a fall in respiratory rate(RR) (Mutoh et al., 1997; Clarke, 1999). Several preanaestheticcombinations have been used prior to sevoflurane anaesthesia(Branson et al., 2001; Mutoh et al., 2002; Polis et al., 2004), butthere have been no studies of the use of sevoflurane in dogssedated with romifidine.Marked synergism between premedication with a2-agonistsedatives and propofol has been reported, demonstrated by adose-related reduction in induction and infusion requirementsfor propofol (Cullen & Reynoldson, 1993; Hammond & England,1994; England et al., 1996b). Romifidine has also been shown tohave a marked anaesthetic-sparing effect on thiopentone andhalothane induction and maintenance of anaesthesia (England H 1 mg/mL) at 40 lg/kg i.v.• R80: romifidine at 80 lg/kg, i.v.• MED: medetomidine (Domtor, Pfizer Salud Animal SA, Madrid,Spain; 1 mg/mL) at 10 lg/kg, i.v.In all protocols, 15 min after sedative administration anaesthe-sia was induced with propofol (Diprivan; ICIFarma, SA Porrin˜oPontevedra, Spain; 10 mg/mL) administered i.v. at a slow dose-to-effect rate with small boluses (0.5 mg/kg, every 30 sec) until