Assessment of a medetomidine/propofol total intravenous anaesthesia (TIVA) for clinical anaesthesia in equidae

This study investigated the clinical use of a medetomidine/propofol TIVA technique in horses.Twenty seven equidae of mixed breed, age [mean (SD (range)] 2.9 ± 2. 74 (0.11-11) years, weight 237 ± 130.22 (64-470) kg (in 12 horses, anaesthetised in the field weight was not scaled but judged by the first authour) were anaesthetised.The following surgeries were performed: intraabdominal (3), castration (15), joint flush (4), screw removal (1), desmotomy (3), dermatoma removal (1).In the field 6 wild horses were premedicated with 0.03 mg/kg acepromazine IM.All the horses were sedated with 7mcg/kg medetomidine IV, anaesthesia was induced 10 minutes later with 2 mg/kg propofol IV.If the patient lifted its head when beeing approached for propofol administration, sedation was deepened with incremental boli of medetomidine.After anaesthesia induction trachea was intubated and oxygen administered at FIO2 >90% in 15 horses.Anaesthesia was maintained with 3.5mcg/kg/h medetomidine IV and propofol infused to effect (initial dose 0.1mg/kg/min).Heart rate, respiratory rate, propofol dose and arterial blood pressure were recorded every five minutes and arterial blood gases every 15 minutes.Quality of sedation, anaesthetic induction and recovery were graded.Arterial bloodpressures and arterial blood gases were analysed in a preliminary manner by descriptive statistical methods.Heart rates and respiratory rates were analysed using ANOVA for repeated measures.To detect differences to preanaesthetic values Dunnett's post test was performed.Eleven horses required additional 2 mcg/kg and one horse 6 mcg/kg medetomidine for adequate sedation prior to induction.Induction of anaesthesia was variable: excellent in 3, good in 18, fair in 4 and poor (unsatisfactory) in 2 horses.In a 28th horse anaesthesia induction was very poor and transfer from induction area to theatre was not possible even after application of several boluses of propofol (total dose 2 mg/kg) and thiopentone (total dose 2.5 mg/kg) as whenever lifted paddeling of the limbs occurred.The use of propofol as an induction agent was stopped after this incidence.After sedation three horses showed second degree AV blocks two of which were treated with atropine.Compared to presedation values respiratory rate as well as heart rate were significantly reduced throughout anaesthesia.During anaesthesia, range of mean values (absolute range) were, for respiratory rate 12.4-17.7 (4-32) breaths/ min, heart rate 36.3-46.8 (15-58) bpm, mean arterial blood pressure 95.6-111 (84-128) mmHg, propofol infusion 0.063-0.18mg/kg/min, p a O 2 23.2-31.8(11.7-59.7)kPa, p a CO 2 6.1-7 (5.2-8.5)kPa.Anaesthetic quality was excellent: spontaneous movement occurred in 6 horses, but was slow and easily controlled with increments of propofol (0.05-0.1 mg/kg).Anaesthetic duration was 57.9 (38.16 (15-175) min.Recovery was completed unaided within 24.3 (10.66 (10-44.8)min.It was uneventful in all horses.Medetomidinepropofol TIVA at dose rates administered in the current study produced good quality anaesthesia with cardiopulmonary depression within ranges commonly recorded during inhalation anaesthesia in horses.However anaesthetic induction was variable, and appeared to be inferior to that achieved with induction regimes including ketamine.