Veterinary Anaesthesia and Analgesia, 2005, 32, 289–296
RESEARCH PAPER
A comparison of propofol, thiopental or ketamine as induction agents in goats Nikitas N Prassinos* DVM, PhD, Apostolos D Galatos* DVM, PhD, Diplomate ECVA & Dimitris Raptopoulos DVM, DrMedVet, DVA, Diplomate ECVA *Clinic of Surgery, Faculty of Veterinary Medicine, University of Thessaly, Greece Clinic of Surgery, Faculty of Veterinary Medicine, Aristotle University of Thessaloniki, Greece
Correspondence: Nikitas N. Prassinos, Clinic of Surgery, Faculty of Veterinary Medicine, University of Thessaly, Trikalon 224, PO Box 199, GR-43100 Karditsa, Greece. E-mail:
[email protected]
Abstract Objective To compare propofol, thiopental and ketamine as induction agents before halothane anaesthesia in goats. Study design Prospective, randomized cross-over study. Animals Seven healthy adult female goats with mean (±SD; range) body mass of 38.9 ± 3.29 kg; 35–45 kg. Methods The seven animals were used on 21 occasions. Each received all three anaesthetics in a randomized cross-over design, with an interval of at least 2 weeks before re-use. Anaesthesia was induced with intravenous (IV) propofol (3 mg kg)1), thiopental (8 mg kg)1, IV) or ketamine (10 mg kg)1, IV). Following tracheal intubation, anaesthesia was maintained with halothane for 30 minutes. Indirect blood pressure, heart rate, respiratory rate and arterial blood gases were monitored. The quality of induction and recovery, recovery times and incidence of side-effects were recorded. Results Induction of anaesthesia was smooth and uneventful, and tracheal intubation was easily performed in all but two goats receiving ketamine. Changes in cardiopulmonary variables and acid–
base status were similar with all three induction agents and were within clinically acceptable limits. Mean recovery times (time to recovery of swallowing reflex and to standing) were significantly shorter, and side-effects, e.g. apnoea, regurgitation, hypersalivation and tympany, were less common in goats receiving propofol, compared with the other treatments. Conclusions and clinical relevance Propofol 3 mg kg)1 IV is superior to thiopental and ketamine as an induction agent before halothane anaesthesia in goats. It provides uneventful recovery which is more rapid than thiopental or ketamine, so reduces anaesthetic risk. Keywords anaesthesia, goat, ketamine, propofol, thiopental.
Introduction Thiopental and ketamine are popular anaesthetics in small ruminants (Gray & McDonell 1986; Riebold 1996) while propofol has been used extensively in animals and human beings. Pharmacokinetic studies in various species have revealed that propofol has a high volume of distribution, rapid metabolism and rapid clearance when given by repeated doses or continuous intravenous (IV) infusion (Langley & Heel 1988; Nolan & Reid 1991; Nolan et al. 1991; Reid et al. 1993; Hall et al. 1994; 289
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Bettschart-Wolfensberger et al. 2000). The rapid onset and short duration of action, with rapid recoveries make the drug potentially useful in ruminants, in which these features are particularly desirable. Reports on the use of propofol for induction and maintenance of anaesthesia have indicated its suitability in goats (Nolan et al. 1991; Reid et al. 1993; Pablo et al. 1997; Carroll et al. 1998). Preliminary trials with propofol in goats, which had not received pre-anaesthetic medication, indicated that a dose of 3 mg kg)1 was sufficient for induction of anaesthesia, producing satisfactory conditions for endotracheal intubation. This dose was lower than those previously described in this species. The effects of thiobarbiturates, ketamine and propofol, combined with either guaifenesin or diazepam, have been compared in sheep (Crump et al. 1994; Vesal et al. 2000), but not, to our knowledge, in goats. The aim of the current study was to compare propofol with thiopental or ketamine as induction agents before halothane anaesthesia in goats. Materials and methods With the approval of the State Veterinary Authorities, seven adult non-pregnant female mixed-bred goats were used on 21 occasions. Their body mass was 38.9 ± 3.29 kg (mean ± SD) and ranged from 35 to 45 kg. The goats were acclimatized to the facility for at least 6 months before the study. They were housed indoors, kept on straw and had free access to hay and water. The animals underwent full pre-anaesthetic screening, i.e. complete physical, haematological and serum biochemical assessments. In each animal, the right carotid artery was relocated subcutaneously at least 2 weeks before the beginning of the experiment. Each animal received all three anaesthetic techniques in a randomized cross-over design, with an interval of at least 2 weeks before re-use. The goats received no pre-anaesthetic medication, were deprived of food for 18 hours, but had free access to water for up to 2 hours before the induction of anaesthesia. The skin overlying the relocated right carotid artery, the left jugular vein and the right distal antebrachium was clipped at least 12 hours before each experiment. These areas were then infiltrated with lidocaine and prepared aseptically. A 20 SWG cannula was inserted into the relocated carotid artery and was secured in place. A second 18 SWG catheter was inserted into 290
the left jugular vein. Catheters were flushed with heparinized saline solution and the goats allowed a 30-minute settling period. Anaesthesia was induced with either propofol (Diprivan; AstraZeneca, Macclesfield, UK; 1% emulsion; 3 mg kg)1) (group P) thiopental (Pentothal; Abbott, Roma, Italy; 2.5% solution; 8 mg kg)1) (group T) or ketamine (Imalgene; Merial, Lyon, France; 10% solution; 10 mg kg)1) (group K), administered IV into the left jugular vein at 1 mL second)1. Once the animals were unable to stand, they were placed in left lateral recumbency and ‘blind’ endotracheal intubation was attempted. Once positioned and secured, the endotracheal tube was connected to an anaesthetic breathing circuit. Anaesthesia was maintained for 30 minutes with halothane (Fluothane; Zeneca, Macclesfield, UK) delivered in oxygen via a semi-closed circle absorption system with an out-of-circuit vaporizer; fresh gas flow was 3 L minute)1. The same vaporizer and anaesthetic circuit were used on all occasions and the soda lime was changed before each experiment. The vaporizer was initially set at 3% until the jaw relaxed and until palpebral and pelvic limb withdrawal reflexes had disappeared. The vaporizer setting was later reduced and held between 1.5 and 2% to sustain this depth of anaesthesia. During anaesthesia, the animals were kept in left lateral recumbency and did not undergo surgery. After discontinuation of halothane, the animals were left to recover undisturbed. The endotracheal tube was removed once swallowing reflex returned. Indirect systolic (SAP), diastolic (DAP) and mean (MAP) blood pressure, and heart rate (HR) were monitored using a Dinamap monitor (Critikon, Tampa, FL, USA), with the cuff (neonatal size no. 5) placed on the right thoracic limb over the radial artery, which was positioned at heart level. Readings were taken immediately before induction, at the time of breathing circuit connection, and at 5, 10, 15, 20 and 30 minutes after connection. Respiratory rate (fr) was counted by observing thoracic wall movements. Blood gas analysis (Radiometer ABL 330, Copenhagen, Denmark) was performed on arterial blood samples taken anaerobically into heparinized syringes at the same time intervals (except at 15 minutes). All samples were stored in ice-water and analysed within 2 hours of collection. Induction time (time from end-injection to recumbency), quality of induction and recovery, and the incidence of side effects, e.g. apnoea (no spontaneous breathing for more than 20 seconds), regur-
Ó Association of Veterinary Anaesthetists, 2005, 32, 289–296
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Table 1 Criteria used to evaluate the quality of induction and recovery, and severity of regurgitation in goats induced with propofol, thiopental or ketamine and maintained with halothane (n ¼ 7) Induction quality scoring* Good ¼ smooth induction, rapidly assumes recumbency, no signs of excitement, easy tracheal intubation Fair ¼ slightly prolonged, mild excitement, reflex response to tracheal intubation Poor ¼ obvious excitement, jumps or attempts to stand after recumbency, inability to intubate trachea Recovery quality scoring* Good ¼ smooth, easy transition to alertness, resumes sternal position, stands in a reasonable amount of time and is able to walk with minimal ataxia Fair ¼ transient excitement or whole body movements, some struggling, hyper-responsiveness that disappears once goat stands unassisted but with moderate ataxia Poor ¼ stereotypical behaviour, e.g. circling, premature attempts to stand, prolonged struggling Regurgitation scoring Mild ¼ detection of ruminal contents within the pharynx or oral cavity Severe ¼ exit of rumen contents through nostrils or mouth *Modified from Lin et al. (1997) and Carroll et al. (1998).
gitation, hypersalivation, tympany, were recorded. Criteria used to evaluate the quality of induction and recovery, and the severity of regurgitation are summarized in Table 1. The presence and extent of excessive salivation and tympany were judged subjectively. The recovery period, which began with the discontinuation of halothane, was divided into four intervals: a) until the return of swallowing reflex, b) until the first head movement, c) until the animal achieved sternal recumbency, d) until the animal could stand unaided. Cardiorespiratory and blood gas data, were analysed using Kruskal–Wallis test, while the Mann– Whitney (U) test was used for between-means comparisons. One-way ANOVA and Duncan’s multiple range test were applied to determine the statistical significance of differences between the means of recovery times. All analyses were performed with the statistical package SPSS (version 11.0 for Windows, SPSS Inc., Chicago, IL, USA). A p-value
