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Zolazepam in Horses Sedated With Medetomidine for Castration Under Field Conditions
Accepted Manuscript Short-term general anaesthesia with tiletamine/zolazepam in horses sedated with medetomidine for castration under field conditions Noemi Romagnoli, Riccardo Rinnovati, Carlotta Lambertini, Alessandro Spadari PII:
S0737-0806(18)30054-6
DOI:
10.1016/j.jevs.2018.03.001
Reference:
YJEVS 2485
To appear in:
Journal of Equine Veterinary Science
Received Date: 23 January 2018 Revised Date:
6 March 2018
Accepted Date: 6 March 2018
Please cite this article as: Romagnoli N, Rinnovati R, Lambertini C, Spadari A, Short-term general anaesthesia with tiletamine/zolazepam in horses sedated with medetomidine for castration under field conditions, Journal of Equine Veterinary Science (2018), doi: 10.1016/j.jevs.2018.03.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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SHORT-TERM GENERAL ANAESTHESIA WITH TILETAMINE/ZOLAZEPAM IN
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HORSES SEDATED WITH MEDETOMIDINE FOR CASTRATION UNDER FIELD
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CONDITIONS.
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Noemi Romagnoli, Riccardo Rinnovati*, Carlotta Lambertini, Alessandro Spadari.
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Department of Veterinary Medical Sciences, Alma Mater University of Bologna, Italy
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*Corresponding author: [email protected]
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Department of Veterinary Medical Sciences, Viua Tolara di Sopra 50, 40064 Ozzano dell’Emila
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Abstract
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The objective of the study is to evaluate the anaesthetic effect produced by the association
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tiletamine/zolazepam in horses sedated with medetomidine undergoing orchiectomy under field
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conditions.
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Ten uncastrated male horses, American Society of Anaesthesiologists (ASA) category I, undergoing
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orchiectomy, were enrolled in the study. The horses received acepromazine (0.03 mg kg-1
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intramuscularly) 30 minutes before sedation with medetomidine (8 µg kg-1 intravenously).
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Anaesthesia was induced with tiletamine/zolazepam (0.7 mg kg-1 IV). During the anaesthesia heart
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rate, pulse quality, respiratory rate, temperature, SpO2, movement and reflexes were measured
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every 5 minutes. Arterial blood gases were evaluated before the premedication and during the
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surgical procedure. The quality of induction and of recovery were recorded.
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The sedation was appropriate, and the quality of recovery was evaluated as good. A statistical
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significant difference was revealed between the basal and intra-anaesthesia heart rate.
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NO differences were observed in blood gas parameters during the procedure
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The results suggested that general anaesthesia produced with tiletamine/zolazepam for induction in
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horses sedated with medetomidine, is suitable during orchiectomy under field conditions.
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Key words: Horse, tiletamine/zolazepam, medetomidine, field castration
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1. Introduction
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In equine field practice, short to medium-term anaesthesia is commonly required for minor surgical
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procedures, such as orchiectomy [1]. 2
ACCEPTED MANUSCRIPT In a field setting, anaesthetic induction and recovery must be gradual and smooth to avoid injuring
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to the horse and to the attending personnel. Field anaesthesia in horses increases the already high
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risk associated with anaesthesia in this species; thus, it should be carried out with more caution than
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under hospital conditions [2], especially due to the absence of cardiovascular monitoring. An
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adequate plane of anaesthesia and analgesia must also be achieved to facilitate surgical
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manipulation [3]. The anaesthetic protocol commonly used in equine practice condition usually
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consist of an association of α2-agonist (detomidine, xylazine or romifidine) and a dissociative agent
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(ketamine) with or without a benzodiazepine [4;5;6]. Among the α2-adrenoceptor agonists,
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medetomidine produces a potent sedative effect at a lower dose than xylazine or even
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dexmedetomidine in horses [7;8]. Medetomidine administered IV at 7 µg kg-1 leads to deep sedation
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characterized by severe ataxia, within 2-7 minutes and lasting up to 20-30 minutes [9]. A recent
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study has already demonstrated the suitability of medetomidine for premedication in equine patients
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in clinical settings undergoing both inhalant and intravenous anaesthesia. [10] However, to the
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authors' knowledge, no studies describe the use of medetomidine in horses under field conditions.
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Among dissociative anaesthetic, tiletamine associated with zolazepam produces a general
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anaesthesia in horses. This association is characterized by gradual induction and by a variable
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recovery quality depending on the dose of tiletamine-zolazepam administered and on the co-
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administered drugs. The recovery quality has been described to be poor when high doses (1-2 mg
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kg-1) are administered and especially when detomidine is used for premedication [11; 12]. The
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response to the tiletamine-zolazepam combination depends on its benzodiazepine component; that
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in dog seems to maintain higher plasma concentration compared to tiletamine [13]. However, no
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pharmacokinetic data are reported for horses.
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The aim of the study was to evaluate the anaesthetic effects produced by tiletamine/zolazepam
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administered for induction of general anaesthesia in horses sedated with medetomidine
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intravenously and undergoing orchiectomy under field conditions.
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ACCEPTED MANUSCRIPT 2. Materials and methods
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2.1 Animals
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Ten client-owned Standardbred horses, undergoing orchiectomy under field conditions, were
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included in the study.
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The patients were considered healthy based on clinical examination, and haematological and
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biochemical evaluation. All the horses included in the study were classified as ASA I.
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The animals care and handling were in accordance with the provisions of the European Economic
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Community Council Directive 86/609, adopted by the Italian Government (
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DL 04/03/14 n°. 26
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2.2 Anaesthesia
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Food, but not water, was withheld for 12 hours before the procedure. The day of the procedure
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horses underwent an anaesthetic examination and both heart rate (HR) and respiratory rate (fR) were
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recorded (baseline values-Tbase). The skin over the right jugular vein was clipped and surgically
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prepared. After a subcutaneous (SC) injection of 2% lidocaine at the aforementioned site, a 14
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Gauge×104 mm jugular catheter was inserted. After catheter placement, acepromazine (ACP)
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(Prequillan, Fatro S.p.A. Ozzano dell’Emilia, BO, Italy) at the dose of 0.03 mg kg-1 was
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administered intramuscularly (IM). Thirty minutes later, sedation was obtained with medetomidine
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(Medetor®, Virbac Milano, Italy) at the dose of 8 µg kg-1, diluted in 20 mL of saline solution, and
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administered by IV over a 2 minutes period. Five minutes later, the quality of sedation was
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evaluated using a sedation score modified from Kloppel and Leece (2011) [13], the score ranged
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from 0 (no sedation) to 3 (marked head resting, without responsiveness) (Table 1). In case of poor
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sedation an adjunctive bolus of medetomidine (1 µg kg-1) was administered IV, while if the sedation
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was evaluated good the anesthesia was induced with tiletamine/zolazepam at the dose of 0.7 mg kg-
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additional bolus of tiletamine/zolazepam 0.25 mg kg-1 would be administered.
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IV (Zoletil 100®, Virbac, Milano, Italy). In case of poor induction with purposeful movement ad
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ACCEPTED MANUSCRIPT The quality of induction was scored with a 0-3 scale (Table 1), as proposed by Marntell et al [2] .
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Induction time was recorded as the time interval from administration of tiletamine/zolazepam to the
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horse achieved recumbency; all the scores were performed by a single expert anaesthetist (NR).
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After induction of anaesthesia, horses were positioned in left lateral recumbency with the upper
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pelvic limb tied at level of pastern with a rope, to perform the orchiectomy. All the surgical
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procedures were carried out by the same surgeon (AS). Five minutes after induction and every five
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minutes up to the end of the anaesthesia, the following parameters were evaluated and recorded:
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heart rate (HR), respiratory rate (fR), arterial oxygen saturation (SpO2), quality of pulse, palpebral
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reflex, nystagmus and ear movements. In addition, at each time point, the degree of muscle
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relaxation was evaluated and scored as proposed by Rossetti and colleagues [24], and the quality of
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analgesia was scored by the surgeon (AS) on a 1-5 scale on the basis of the horse’s “reactions”
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observed during application of the surgical stimuli as described by Marntell et al [2]. The degree of
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muscle relaxation and analgesia are summarized in Table 1. If insufficient muscle relaxation or
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movements were observed, an additional dose of the tiletamine/zolazepam combination (0.15 mg
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kg-1) was administered IV. The time of administration and the number of additional doses were
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recorded. The total time from induction to achieve sternal and standing position were recorded.
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Saline solution was administered intravenously throughout the anaesthesia at the rate of 4 mL kg-1h-
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1
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At the end of the surgical procedure the horses were sedated with medetomidine at the dose of 2 µg
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kg-1), diluted in 5 mL saline solution and administered IV over 2 minutes. The quality of the
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recovery was evaluated using a score modified from Valverde et al. [14] to suit the field conditions.
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This scoring system consisted of 8 quality-defined categories each with separate scores (Table 1).
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The total recovery score was matched to a final descriptive recovery score (1-6) with 1 representing
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the best recovery and 6 describing a poor recovery associated with an accident.
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ACCEPTED MANUSCRIPT At the end of the surgery, flunixine meglumine (1.1 mg kg-1 IV) and penicillin/streptomycin (12 mg
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kg-1 IM) were administered. As soon as the horse reached the standing position, the IV catheter was
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removed.
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2.3 Samples collection
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Soon after the jugular catheter placement and before premedication ten mL of blood were collected
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from the jugular catheter before premedication. An aliquot of 5 mL of blood was collected in
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K3EDTA and used to perform a CBC count . The second 5 mL aliquot of blood was collected into
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serum vials, centrifuged at 3500 rpm for ten minutes within one week and used to perform
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biochemical profile. One mL of arterial blood was withdrawn anaerobically, with pre-eparinized
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syringe (Monovette- Sarstedt, Germany) from the transverse facial artery before, 15 and 30 minutes
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after induction. Arterial sample was used to perform blood gas analysis (pH, pCO2, HCO3-, pCO2,
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Hb) (ABL700 Flex radiometer analyser, Radiometer medical ApS, Brønshøj, Denmark).
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2.4 Statistical analysis
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The sedation, induction, recovery score were reported as median and range. A descriptive statistic
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was carried out for the anaesthetic parameters. Cardiorespiratory and blood gas parameters were
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check for normality using a Shapiro Wilk test. Cardiorespiratory parameters which were normally
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distributed: values from each time point were compared with Tbase using a T-test for paired
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samples and are reported as mean and standard deviation (SD). Blood gas values were not normally
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distributed: Blood gas values at T15 and T30 were compared with a Wilcoxon paired test and they
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are reported as median and range. The level of significance was set at p< 0.05. The statistical
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analysis was carried out using computer software (Med-Calc 12.7.5, MedCalc Software, Acacialaan
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22, B-8400 Ostend, Belgium).
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3. Results
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All horses included completed the study. The median age of the horses was 3 years (range 1.5-10
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years) and the median bodyweight was 445 (range 250-540) kg. Mean surgical time was 30.9 ±1.2
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minutes.
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ACCEPTED MANUSCRIPT Scores for the quality of sedation, induction and recovery, the time for induction and the time to
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achieve sternal recumbency and standing position, as well as the degree of muscle relaxation and
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analgesia are summarized in Table 2.
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Median sedation score was 3 (range 2-3): all horses were effectively sedated five minutes after
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medetomidine administration with the exception of one horse (No. 8) which was only lightly
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sedated (score 2).
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The median induction time after tiletamine/zolazepam administration was 47 seconds (range 35 to
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65). The quality of induction was considered excellent (median 3; range 1-3), with the exception of
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only one horse (1/10) which had a poor induction due to limb movements when placed in lateral
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recumbency.
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tiletamine/zolazepam: one horse (1/3)required two additional doses because of movements in
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association with surgical stimulation while, in another two horses (2/3), one additional bolus was
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necessary to reduce the elevated contraction of the cremaster muscle during surgical traction.
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However, the median degree of analgesia was scored as 5 (range 2-5). The recovery was smooth
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and without excitation. Eight out of ten horses reached a standing position at the first attempt (score
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1). The horses in which an additional bolus of tiletamine/zolazepam was administered showed
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longer and more pronounced ataxia and required a greater number of attempts to achieve a standing
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position (score 4 and 2, in horses No. 3 and 1 respectively).
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Cardiorespiratory parameters are reported in Table 3. Heart rate decreased significantly (p<0.05)
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after induction and remained low throughout anaesthesia; the greatest reduction, compared to the
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baseline values, was at 20 minutes (mean heart rate 28.6±4 beats min-1) after the
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tiletamine/zolazepam injection. The quality of pulse was strong during all the procedure. The
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respiratory rate did not differ significantly from baseline.
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Results concerning blood gas analysis were reported in table 4. Values at 15 and 30 minutes after
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induction did not differ from baseline (Table 4).
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The palpebral reflex was maintained in all horses throughout the anaesthesia; nystagmus appeared
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in all animals approximately 20 minutes after induction and, in two horses, after 10 minutes from
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induction. Ear movement appeared 20 minutes after induction in only two horses.
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4. Discussion
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In the present study, tiletamine/zolazepam association produced a good quality anaesthesia in
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horses sedated with medetomidine and undergoing orchiectomy under field conditions. A bilateral
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orchiectomy was considered to be a type of surgical procedure well suited for field conditions and a
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good model to verify the feasibility of the anaesthetic protocol, as described by other authors
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[13;15;16].
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Acepromazine, administered intramuscularly 30 minutes before induction, allowed tranquilization
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of the patient and reduced the anaesthetic risks that have been commonly associated with equine
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general anaesthesia, as previously observed by Johonston et al. (2002) [17]. However, 30 minutes
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after the injection of the ACP, no sign of sedation was recorded probably due to the low dosage
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used in this study
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In the present study, at every time point a relevant bradycardia has been recorded in the horses.
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However, bradycardia was not clinically relevant if it is related to the strong pulse pressure detected
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during surgical procedure and the absence of hypoxaemia. Alpha2-agonists commonly induce a
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peripheral vasoconstriction with reflex bradycardia and medetomidine has already been described to
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produce a significant decrease in HR, atrioventricular blocks and hypertension when administered
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in horses at dosages of 5 to 10 µg kg-1 [18]. We did not evaluate the blood pressure: although it is
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routinely performed under clinical conditions, it is unusual during anaesthesia under field
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conditions.
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When medetomidine was administered by constant rate infusion intraoperatively an high mean
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arterial blood pressure was observed when compared with horses receiving lidocaine [5].
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ACCEPTED MANUSCRIPT In laterally recumbent horses anaesthetized under field conditions, hypoxemia is the most relevant
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side effect since all general anaesthetic exert a respiratory depression. However, in this setting
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intubation or oxygen supply are usually not performed. especially for such short procedure. In the
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present study the fR did not differ significantly from baseline, as well as a significantly change in
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PaO2 and PaCO2 has not been observed in the blood gas, obtained during the surgical procedure.
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They were always into acceptable limits as reported by Wan et al. (1992) [19]. Moreover, in the
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present study the author supposed that the protocol permitted to maintain a high respiratory rate
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that, together with breathing room air (FiO2 0.21), compensated for the lung compression and
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atelectasis, reducing the risk for hypoxemia.
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Tiletamine, used in association with xylazine or detomidine in horses, has been reported to produce
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good quality induction, but the recovery has been classified as poor [20;21]. In the present study the
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induction after tiletamine/zolazepam administration was rapid and gradual as previously described
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by other authors [20;22]; the induction times were similar to those obtained by induction with
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ketamine/diazepam [6;11;13;15;23;24]. In addition, tiletamine, as a dissociative drug, produces an
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increase in sympathetic tone and an increase in HR which usually counteract the alpha2-agonists
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induced bradycardia.
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A good recovery quality is pivotal for a safe equine anaesthetic regimen. Johnson et al. (2002) [17]
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reported that 25.6% of all horses died from anaesthesia due to fatal injuries which occurred during
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the recovery period. In this study, the recovery was excellent (score 1) in 8 patients out of ten
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(80%). The overall recovery quality of the present study was better if compared with previous
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studies in which medetomidine and ketamine anaesthesia was used and the median score for
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recovery was 2. The good results could be related to the administration of medetomidine at the end
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of the surgery to provide sedation prior to the recovery. Santos et al. [25] concluded that the
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administration of the alpha2-agonists to horses during the recovery period prolonged, but improved,
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recovery from isoflurane anaesthesia. Recovery became more gradual, free from excitation and
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ataxia with minimal cardiopulmonary effects. In the present study, medetomidine administration
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ACCEPTED MANUSCRIPT contributed to reduce the undesirable effects described in a paper in which the combination of
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tiletamine/zolazepam was administered for induction of general anaesthesia [11].
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A limit of the present study was the small number of the animals and the lack of comparison with
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another treatment group for example a group of horses anaesthetized with ketamine and
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benzodiazepines, the most common equine induction anaesthesia protocol.
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Conclusions
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Anaesthesia and analgesia obtained with this protocol was good; only two horse required a
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boostinjection of tiletamine/zolazepam due to the contraction of the cremaster muscle against the
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traction by the surgeon. In conclusio the combination of tiletamine/zolazepam administered for
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induction of general anaesthesia in horses receiving medetomidine as premedicant drug is effective
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for short term procedures in healthy horses under field conditions. This combination produced
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adequate analgesia and muscle relaxation besides minimal side effects and good induction and
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recovery quality.
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Authors’ declaration of interests
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No competing interests have been declared.
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Ethical animal research
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The study was approved by Bologna University Ethics and Welfare Committee (Protocol n°19413-
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X/10 del 04.05.2011). Owner consent was obtained in all cases.
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Acknowledgements
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The authors than Dr. Barbara Pasqualucci for the support during data collection.
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ACCEPTED MANUSCRIPT Score 0 1 2 3
Quality of sedation Unsatisfactory sedation, minimal or no signs of sedation Mild sedation with head drop slightly lowered Moderate sedation with head lowered, mild ataxia Marked, profound sedation and ataxia
0 1 2
Degree of muscle relaxation Good: complete relaxation, no resistance to limb manipulation Acceptable: muscular rigidity Poor: spontaneous motor activity, struggling during manipulation
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Degree of analgesia Kicking Distinct limb movement Reaction during skin incision and/or clamping of the spermatic cord Minimal reaction during skin incision and/or clamping of the spermatic cord No reaction
A 1 2 3 4 B 1 2 3 C 1 2 3 D 1 2 3 4 E 1 2 3
Quality of recovery Overall attitude Calm Calme/determined Confused, dizzy Frantic Move to sternal Smooth, methodical Fighting mat, but controlled Crashing, flopping over Sternal phase An organised pause Nonexistant Multiple, with struggle Move to stand Methodical An organised scramble Used walls for support Ricocheting off walls Strength Near full Mildly rubbery Dog-sitting before standing
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Quality of induction anesthesia Poor: the horse was induced with considerable movement and/or excitement; the horse may have made subsequent attempts to stand or any other situation that could have resulted in injury Fair: the recumbency achieved, the horse fell without relaxation of limbs or with a strong forward or backward movement Good: smooth induction, but horse showed head or limb twitching after induction or a tendency to walk forward or backwards after induction agent was administered Excellent: smooth induction, no muscle twitching. Absent forward or backwards movements
ACCEPTED MANUSCRIPT Repeated attempts due to weakness No. attempts to stand (No. = score) Balance and coordination Solid Moderate ‘dancing’ Reflex saves Careening Falls back down Knuckling None Hindlimbs only All four limbs
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4 F G 1 2 3 4 5 H 1 2 3
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TABLE 1: Scoring system applied for evaluation of the quality of sedation and induction, degree of muscle relaxation and analgesia. The sedation score was modified from Kloppel and Leece (2011).
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Induction score (0-3) 3 (1-3)
Degree of muscle relaxation (0-2) 0 (0-2)
Degree of analgesia (1-5) 5 (2-5)
Induction time (sec)
Time to sternal recumbency (min) 59 (52-97)
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Time to recumbency (sec) 47 (35-65)
47 (35-65)
Time to standing (min) 64 (56-99)
Recovery score (1-6) 1 (1-4)
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Sedation score (0-3) Median 3 Range (2-3)
Table 2: Sedation score, time to recumbency, induction score, degree of muscle relaxation, degree of analgesia, time sternal recumbency, time to
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standing and recovery score in 10 horses undergoing field anaesthesia for orchiectomy. Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1)
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intravenously. At the end of the surgery horses received medetomidine (2 µg kg-1) intravenously. Data are reported as median and range.
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HR (beats/min) fR (breath/min)
Tbaseline
5
10
15
20
25
30
40 (32-52)
30.1 ± 3.8* 11.9 ± 6.5 92.9 ± 4.6
30.3 ± 4.0* 12.0 ± 6.4 94.0 ± 1.8
30.7 ± 3.5* 10.5 ± 14.5 94.3 ± 3.7
28.6 ± 4.0* 15.5 ± 7.9 92.8 ± 5.1
29.7 ± 4.8* 16.3 ± 6.5 93.3 ± 4.8
30.9 ± 4.6* 17.6 ± 6.9 94.0 ± 3.5
16.6 ± 4.8
SpO2 (%)
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Variables
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Table 3: Heart rate (HR), respiratory rate (fR) and arterial oxygen saturation (SpO2) in 10 horses undergoing field anaesthesia for orchiectomy. Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with
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tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1) intravenously. At the end of the surgery horses
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received medetomidine (2 µg kg-1) intravenously. Data are reported as median and range.
Tbase T15 T30 pH 7.4 7.4 7.4 HCO3 28.6 ± 2.4 28.5 ± 1.7 29.1 ± 2.0 PaCO2 mmHg 47.6 ± 5.6 47.9 ± 3.0 48.2 ± 4.4 PaO2 mmHg 103.4 ± 35.5 88.8 ± 28.2 84.1 ± 14.7 SO2 (%) 92.7 ± 6.2 93.9 ± 2.3 94.3 ± 3.3 Hb (g/dL) 11.4 ± 2.0 11.1 ± 3.3 10.5 ± 3.1 Table 4- Blood gas values in 10 horses undergoing field anaesthesia for orchiectomy.
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Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1) intravenously. At the end of the surgery horses received
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medetomidine (2 µg kg-1) intravenously. Data are reported as median and standard deviation.
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ACCEPTED MANUSCRIPT Highlights: In equine field practice, short to medium-term anaesthesia is commonly required for minor surgical procedures
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In laterally recumbent horses anaesthetized under field conditions, hypoxemia is the most relevant side effect
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In the present study, tiletamine/zolazepam association produced a good quality anaesthesia
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The anaesthesia and analgesia obtained with this protocol was good
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ACCEPTED MANUSCRIPT Ethical animal research
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The study was approved by Bologna University Ethics and Welfare Committee. Owner consent was obtained in all cases.
ACCEPTED MANUSCRIPT Authors’ declaration of interests
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No competing interests have been declared.
S0737-0806(18)30054-6
DOI:
10.1016/j.jevs.2018.03.001
Reference:
YJEVS 2485
To appear in:
Journal of Equine Veterinary Science
Received Date: 23 January 2018 Revised Date:
6 March 2018
Accepted Date: 6 March 2018
Please cite this article as: Romagnoli N, Rinnovati R, Lambertini C, Spadari A, Short-term general anaesthesia with tiletamine/zolazepam in horses sedated with medetomidine for castration under field conditions, Journal of Equine Veterinary Science (2018), doi: 10.1016/j.jevs.2018.03.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
SHORT-TERM GENERAL ANAESTHESIA WITH TILETAMINE/ZOLAZEPAM IN
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HORSES SEDATED WITH MEDETOMIDINE FOR CASTRATION UNDER FIELD
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CONDITIONS.
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Noemi Romagnoli, Riccardo Rinnovati*, Carlotta Lambertini, Alessandro Spadari.
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Department of Veterinary Medical Sciences, Alma Mater University of Bologna, Italy
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*Corresponding author: [email protected]
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Department of Veterinary Medical Sciences, Viua Tolara di Sopra 50, 40064 Ozzano dell’Emila
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(BO)
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Abstract
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The objective of the study is to evaluate the anaesthetic effect produced by the association
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tiletamine/zolazepam in horses sedated with medetomidine undergoing orchiectomy under field
31
conditions.
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Ten uncastrated male horses, American Society of Anaesthesiologists (ASA) category I, undergoing
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orchiectomy, were enrolled in the study. The horses received acepromazine (0.03 mg kg-1
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intramuscularly) 30 minutes before sedation with medetomidine (8 µg kg-1 intravenously).
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Anaesthesia was induced with tiletamine/zolazepam (0.7 mg kg-1 IV). During the anaesthesia heart
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rate, pulse quality, respiratory rate, temperature, SpO2, movement and reflexes were measured
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every 5 minutes. Arterial blood gases were evaluated before the premedication and during the
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surgical procedure. The quality of induction and of recovery were recorded.
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The sedation was appropriate, and the quality of recovery was evaluated as good. A statistical
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significant difference was revealed between the basal and intra-anaesthesia heart rate.
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NO differences were observed in blood gas parameters during the procedure
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The results suggested that general anaesthesia produced with tiletamine/zolazepam for induction in
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horses sedated with medetomidine, is suitable during orchiectomy under field conditions.
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Key words: Horse, tiletamine/zolazepam, medetomidine, field castration
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1. Introduction
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In equine field practice, short to medium-term anaesthesia is commonly required for minor surgical
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procedures, such as orchiectomy [1]. 2
ACCEPTED MANUSCRIPT In a field setting, anaesthetic induction and recovery must be gradual and smooth to avoid injuring
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to the horse and to the attending personnel. Field anaesthesia in horses increases the already high
55
risk associated with anaesthesia in this species; thus, it should be carried out with more caution than
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under hospital conditions [2], especially due to the absence of cardiovascular monitoring. An
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adequate plane of anaesthesia and analgesia must also be achieved to facilitate surgical
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manipulation [3]. The anaesthetic protocol commonly used in equine practice condition usually
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consist of an association of α2-agonist (detomidine, xylazine or romifidine) and a dissociative agent
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(ketamine) with or without a benzodiazepine [4;5;6]. Among the α2-adrenoceptor agonists,
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medetomidine produces a potent sedative effect at a lower dose than xylazine or even
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dexmedetomidine in horses [7;8]. Medetomidine administered IV at 7 µg kg-1 leads to deep sedation
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characterized by severe ataxia, within 2-7 minutes and lasting up to 20-30 minutes [9]. A recent
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study has already demonstrated the suitability of medetomidine for premedication in equine patients
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in clinical settings undergoing both inhalant and intravenous anaesthesia. [10] However, to the
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authors' knowledge, no studies describe the use of medetomidine in horses under field conditions.
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Among dissociative anaesthetic, tiletamine associated with zolazepam produces a general
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anaesthesia in horses. This association is characterized by gradual induction and by a variable
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recovery quality depending on the dose of tiletamine-zolazepam administered and on the co-
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administered drugs. The recovery quality has been described to be poor when high doses (1-2 mg
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kg-1) are administered and especially when detomidine is used for premedication [11; 12]. The
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response to the tiletamine-zolazepam combination depends on its benzodiazepine component; that
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in dog seems to maintain higher plasma concentration compared to tiletamine [13]. However, no
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pharmacokinetic data are reported for horses.
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The aim of the study was to evaluate the anaesthetic effects produced by tiletamine/zolazepam
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administered for induction of general anaesthesia in horses sedated with medetomidine
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intravenously and undergoing orchiectomy under field conditions.
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ACCEPTED MANUSCRIPT 2. Materials and methods
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2.1 Animals
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Ten client-owned Standardbred horses, undergoing orchiectomy under field conditions, were
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included in the study.
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The patients were considered healthy based on clinical examination, and haematological and
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biochemical evaluation. All the horses included in the study were classified as ASA I.
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The animals care and handling were in accordance with the provisions of the European Economic
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Community Council Directive 86/609, adopted by the Italian Government (
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DL 04/03/14 n°. 26
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2.2 Anaesthesia
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Food, but not water, was withheld for 12 hours before the procedure. The day of the procedure
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horses underwent an anaesthetic examination and both heart rate (HR) and respiratory rate (fR) were
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recorded (baseline values-Tbase). The skin over the right jugular vein was clipped and surgically
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prepared. After a subcutaneous (SC) injection of 2% lidocaine at the aforementioned site, a 14
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Gauge×104 mm jugular catheter was inserted. After catheter placement, acepromazine (ACP)
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(Prequillan, Fatro S.p.A. Ozzano dell’Emilia, BO, Italy) at the dose of 0.03 mg kg-1 was
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administered intramuscularly (IM). Thirty minutes later, sedation was obtained with medetomidine
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(Medetor®, Virbac Milano, Italy) at the dose of 8 µg kg-1, diluted in 20 mL of saline solution, and
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administered by IV over a 2 minutes period. Five minutes later, the quality of sedation was
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evaluated using a sedation score modified from Kloppel and Leece (2011) [13], the score ranged
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from 0 (no sedation) to 3 (marked head resting, without responsiveness) (Table 1). In case of poor
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sedation an adjunctive bolus of medetomidine (1 µg kg-1) was administered IV, while if the sedation
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was evaluated good the anesthesia was induced with tiletamine/zolazepam at the dose of 0.7 mg kg-
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1
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additional bolus of tiletamine/zolazepam 0.25 mg kg-1 would be administered.
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IV (Zoletil 100®, Virbac, Milano, Italy). In case of poor induction with purposeful movement ad
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ACCEPTED MANUSCRIPT The quality of induction was scored with a 0-3 scale (Table 1), as proposed by Marntell et al [2] .
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Induction time was recorded as the time interval from administration of tiletamine/zolazepam to the
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horse achieved recumbency; all the scores were performed by a single expert anaesthetist (NR).
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After induction of anaesthesia, horses were positioned in left lateral recumbency with the upper
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pelvic limb tied at level of pastern with a rope, to perform the orchiectomy. All the surgical
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procedures were carried out by the same surgeon (AS). Five minutes after induction and every five
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minutes up to the end of the anaesthesia, the following parameters were evaluated and recorded:
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heart rate (HR), respiratory rate (fR), arterial oxygen saturation (SpO2), quality of pulse, palpebral
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reflex, nystagmus and ear movements. In addition, at each time point, the degree of muscle
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relaxation was evaluated and scored as proposed by Rossetti and colleagues [24], and the quality of
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analgesia was scored by the surgeon (AS) on a 1-5 scale on the basis of the horse’s “reactions”
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observed during application of the surgical stimuli as described by Marntell et al [2]. The degree of
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muscle relaxation and analgesia are summarized in Table 1. If insufficient muscle relaxation or
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movements were observed, an additional dose of the tiletamine/zolazepam combination (0.15 mg
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kg-1) was administered IV. The time of administration and the number of additional doses were
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recorded. The total time from induction to achieve sternal and standing position were recorded.
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Saline solution was administered intravenously throughout the anaesthesia at the rate of 4 mL kg-1h-
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1
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At the end of the surgical procedure the horses were sedated with medetomidine at the dose of 2 µg
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kg-1), diluted in 5 mL saline solution and administered IV over 2 minutes. The quality of the
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recovery was evaluated using a score modified from Valverde et al. [14] to suit the field conditions.
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This scoring system consisted of 8 quality-defined categories each with separate scores (Table 1).
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The total recovery score was matched to a final descriptive recovery score (1-6) with 1 representing
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the best recovery and 6 describing a poor recovery associated with an accident.
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ACCEPTED MANUSCRIPT At the end of the surgery, flunixine meglumine (1.1 mg kg-1 IV) and penicillin/streptomycin (12 mg
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kg-1 IM) were administered. As soon as the horse reached the standing position, the IV catheter was
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removed.
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2.3 Samples collection
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Soon after the jugular catheter placement and before premedication ten mL of blood were collected
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from the jugular catheter before premedication. An aliquot of 5 mL of blood was collected in
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K3EDTA and used to perform a CBC count . The second 5 mL aliquot of blood was collected into
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serum vials, centrifuged at 3500 rpm for ten minutes within one week and used to perform
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biochemical profile. One mL of arterial blood was withdrawn anaerobically, with pre-eparinized
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syringe (Monovette- Sarstedt, Germany) from the transverse facial artery before, 15 and 30 minutes
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after induction. Arterial sample was used to perform blood gas analysis (pH, pCO2, HCO3-, pCO2,
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Hb) (ABL700 Flex radiometer analyser, Radiometer medical ApS, Brønshøj, Denmark).
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2.4 Statistical analysis
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The sedation, induction, recovery score were reported as median and range. A descriptive statistic
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was carried out for the anaesthetic parameters. Cardiorespiratory and blood gas parameters were
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check for normality using a Shapiro Wilk test. Cardiorespiratory parameters which were normally
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distributed: values from each time point were compared with Tbase using a T-test for paired
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samples and are reported as mean and standard deviation (SD). Blood gas values were not normally
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distributed: Blood gas values at T15 and T30 were compared with a Wilcoxon paired test and they
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are reported as median and range. The level of significance was set at p< 0.05. The statistical
148
analysis was carried out using computer software (Med-Calc 12.7.5, MedCalc Software, Acacialaan
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22, B-8400 Ostend, Belgium).
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3. Results
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All horses included completed the study. The median age of the horses was 3 years (range 1.5-10
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years) and the median bodyweight was 445 (range 250-540) kg. Mean surgical time was 30.9 ±1.2
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minutes.
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ACCEPTED MANUSCRIPT Scores for the quality of sedation, induction and recovery, the time for induction and the time to
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achieve sternal recumbency and standing position, as well as the degree of muscle relaxation and
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analgesia are summarized in Table 2.
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Median sedation score was 3 (range 2-3): all horses were effectively sedated five minutes after
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medetomidine administration with the exception of one horse (No. 8) which was only lightly
159
sedated (score 2).
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The median induction time after tiletamine/zolazepam administration was 47 seconds (range 35 to
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65). The quality of induction was considered excellent (median 3; range 1-3), with the exception of
162
only one horse (1/10) which had a poor induction due to limb movements when placed in lateral
163
recumbency.
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tiletamine/zolazepam: one horse (1/3)required two additional doses because of movements in
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association with surgical stimulation while, in another two horses (2/3), one additional bolus was
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necessary to reduce the elevated contraction of the cremaster muscle during surgical traction.
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However, the median degree of analgesia was scored as 5 (range 2-5). The recovery was smooth
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and without excitation. Eight out of ten horses reached a standing position at the first attempt (score
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1). The horses in which an additional bolus of tiletamine/zolazepam was administered showed
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longer and more pronounced ataxia and required a greater number of attempts to achieve a standing
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position (score 4 and 2, in horses No. 3 and 1 respectively).
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Cardiorespiratory parameters are reported in Table 3. Heart rate decreased significantly (p<0.05)
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after induction and remained low throughout anaesthesia; the greatest reduction, compared to the
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baseline values, was at 20 minutes (mean heart rate 28.6±4 beats min-1) after the
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tiletamine/zolazepam injection. The quality of pulse was strong during all the procedure. The
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respiratory rate did not differ significantly from baseline.
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Results concerning blood gas analysis were reported in table 4. Values at 15 and 30 minutes after
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induction did not differ from baseline (Table 4).
three
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The palpebral reflex was maintained in all horses throughout the anaesthesia; nystagmus appeared
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in all animals approximately 20 minutes after induction and, in two horses, after 10 minutes from
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induction. Ear movement appeared 20 minutes after induction in only two horses.
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4. Discussion
184
In the present study, tiletamine/zolazepam association produced a good quality anaesthesia in
185
horses sedated with medetomidine and undergoing orchiectomy under field conditions. A bilateral
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orchiectomy was considered to be a type of surgical procedure well suited for field conditions and a
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good model to verify the feasibility of the anaesthetic protocol, as described by other authors
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[13;15;16].
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Acepromazine, administered intramuscularly 30 minutes before induction, allowed tranquilization
190
of the patient and reduced the anaesthetic risks that have been commonly associated with equine
191
general anaesthesia, as previously observed by Johonston et al. (2002) [17]. However, 30 minutes
192
after the injection of the ACP, no sign of sedation was recorded probably due to the low dosage
193
used in this study
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In the present study, at every time point a relevant bradycardia has been recorded in the horses.
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However, bradycardia was not clinically relevant if it is related to the strong pulse pressure detected
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during surgical procedure and the absence of hypoxaemia. Alpha2-agonists commonly induce a
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peripheral vasoconstriction with reflex bradycardia and medetomidine has already been described to
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produce a significant decrease in HR, atrioventricular blocks and hypertension when administered
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in horses at dosages of 5 to 10 µg kg-1 [18]. We did not evaluate the blood pressure: although it is
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routinely performed under clinical conditions, it is unusual during anaesthesia under field
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conditions.
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When medetomidine was administered by constant rate infusion intraoperatively an high mean
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arterial blood pressure was observed when compared with horses receiving lidocaine [5].
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side effect since all general anaesthetic exert a respiratory depression. However, in this setting
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intubation or oxygen supply are usually not performed. especially for such short procedure. In the
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present study the fR did not differ significantly from baseline, as well as a significantly change in
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PaO2 and PaCO2 has not been observed in the blood gas, obtained during the surgical procedure.
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They were always into acceptable limits as reported by Wan et al. (1992) [19]. Moreover, in the
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present study the author supposed that the protocol permitted to maintain a high respiratory rate
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that, together with breathing room air (FiO2 0.21), compensated for the lung compression and
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atelectasis, reducing the risk for hypoxemia.
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Tiletamine, used in association with xylazine or detomidine in horses, has been reported to produce
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good quality induction, but the recovery has been classified as poor [20;21]. In the present study the
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induction after tiletamine/zolazepam administration was rapid and gradual as previously described
216
by other authors [20;22]; the induction times were similar to those obtained by induction with
217
ketamine/diazepam [6;11;13;15;23;24]. In addition, tiletamine, as a dissociative drug, produces an
218
increase in sympathetic tone and an increase in HR which usually counteract the alpha2-agonists
219
induced bradycardia.
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A good recovery quality is pivotal for a safe equine anaesthetic regimen. Johnson et al. (2002) [17]
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reported that 25.6% of all horses died from anaesthesia due to fatal injuries which occurred during
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the recovery period. In this study, the recovery was excellent (score 1) in 8 patients out of ten
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(80%). The overall recovery quality of the present study was better if compared with previous
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studies in which medetomidine and ketamine anaesthesia was used and the median score for
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recovery was 2. The good results could be related to the administration of medetomidine at the end
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of the surgery to provide sedation prior to the recovery. Santos et al. [25] concluded that the
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administration of the alpha2-agonists to horses during the recovery period prolonged, but improved,
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recovery from isoflurane anaesthesia. Recovery became more gradual, free from excitation and
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ataxia with minimal cardiopulmonary effects. In the present study, medetomidine administration
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ACCEPTED MANUSCRIPT contributed to reduce the undesirable effects described in a paper in which the combination of
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tiletamine/zolazepam was administered for induction of general anaesthesia [11].
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A limit of the present study was the small number of the animals and the lack of comparison with
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another treatment group for example a group of horses anaesthetized with ketamine and
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benzodiazepines, the most common equine induction anaesthesia protocol.
235
Conclusions
236
Anaesthesia and analgesia obtained with this protocol was good; only two horse required a
237
boostinjection of tiletamine/zolazepam due to the contraction of the cremaster muscle against the
238
traction by the surgeon. In conclusio the combination of tiletamine/zolazepam administered for
239
induction of general anaesthesia in horses receiving medetomidine as premedicant drug is effective
240
for short term procedures in healthy horses under field conditions. This combination produced
241
adequate analgesia and muscle relaxation besides minimal side effects and good induction and
242
recovery quality.
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Authors’ declaration of interests
244
No competing interests have been declared.
245
Ethical animal research
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The study was approved by Bologna University Ethics and Welfare Committee (Protocol n°19413-
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X/10 del 04.05.2011). Owner consent was obtained in all cases.
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Acknowledgements
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The authors than Dr. Barbara Pasqualucci for the support during data collection.
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[9] Bettschart-Wolfensberger R, Clarke KW, Vainio O, Shojaee Aliabadis F, and Demuth D.
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Pharmacokinetics of medetomidine in ponies and elaboration of a medetomidine infusion regime
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which provides a constant level of sedation. Res Vet Sc 1999; 67: 41-6.
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[10] Bettschart-Wolfensberger R, Dicht S, Vullo C, Frotzler A, Kuemmerle JM, Ringer SK. A
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clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol
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constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery
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characteristics. Vet Anaesth Analg 2011; 38:186-94.
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[11] Muir WW, Lerche P, Robertson JT, Hubbell JAE, Beard W, Miller, T et al. Comparison of
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four drug combinations for total intravenous anesthesia of horses undergoing surgical removal of an
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abdominal testis. J Am Vet Med Ass. 2000; 217:869-73.
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ACCEPTED MANUSCRIPT [12] Lopez MA, Jiménez J, Martìn MF, Usόn JM, Pérez, EM, Ezquerra LJ. Tiletamine-Zolazepam
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anesthesia in horse: repeated dose versus continuous infusion. Revue de Méd Vét 2004; 155:197-
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204.
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[13] Kyeumhan N, Kil-Soo K, Byoungki A, Pillippe A, Tae-Ho O, Wonku K. Simultaneous
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determination of zolazepam and tiletamine in dog plasma by liquid chromatography coupled to a
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tandem mass spectrometry. Biomed Chromatogr 2012; 26: 1133–1136.
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[14] Valverde A, Gunkelt C, Doherty TJ., Giguère S, Pollak AS. Effect of a constant rate infusion
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of lidocaine on the quality of recovery from sevoflurane or isoflurane general anaesthesia in horses.
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Equine Vet J 2005; 37:559-64.
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[15] Sinclair MD, Valverde, A. Short-term anaesthesia with xylazine, diazepam/ketamine for
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castration under field conditions: use of intravenous lidocaine. Equine Vet J 2009; 41:149-52.
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[16] Corletto F, Raisis AA, Brearley JC. Comparison of morphine and butorphanol as pre-
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anesthetic agents in combination with romifidine for field castration in ponies. Vet Anaesth Anal
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2005; 32:16-22.
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[17] Johnston GM, Eastment, JK., Wood J, Taylor PM. The confidential enquiry into perioperative
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equine fatalities (CEPEF): mortality results of phase 1 and 2. Vet Anaesth and Analg 2002; 29:159-
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70.
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[18] Yamashita K, Tsubakishita S, Futaoka S, Ueda I, Hamaguchi H, Seno T et al. Cardiovascular
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effect of Medetomidine, Detomidine and Xylazine in horses. J Vet Med Sc2000; 62: 1025-32.
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anesthesia in horses. Vet Surg 1992; 21: 312-18.
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[20] Cuvelliez S, Rosseel G, Blais D, Salmon Y, Troncy E, Larivière N. L’anesthésie intraveineuse
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ACCEPTED MANUSCRIPT [21] Bouts T, Gasthuys F, Vlaminck L, Van Branteghem L. Comparison of romifidine-ketamine-
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midazolam and romifidine-tiletamine-zolazepam total intravenous anaesthesia (TIVA) for clinical
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anaesthesia in horses. Vet Anesth and Analg 2002; 29: 90-6.
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[22] Lin HC, Branson KR, Thurmon, JC, Benson, GJ, Tranquilli WJ, Olson WA et al. Ketamine,
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Telazol, xylazine and detomidine. A comparative anesthetic drug combinations study in ponies.
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Acta Vet Scand 1992; 33:109-15.
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[23] Brock N,Hildebrand SV. A comparison of xylazine-diazepam-ketamine and xylazine-
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guaifenesin-ketamine in equine anesthesia. Vet Sur 1990; 19: 468-74.
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[24] Rossetti RB, Gaido Cortopassi SR, Intelizzano T, De Lima Machado TS, Ferreira da Cruz RS.
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Comparison of ketamine and S(+)-ketamine, with romifidine and diazepam, for total intravenous
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anesthesia in horse. Vet Anaesth and Analg 2008; 35:30-7.
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[25] Santos M, Fuente M, Garcia-Iturralde R, Herran R, Lopez-Sanroman J, Tendillo FJ. Effects of
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alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses. Equine Vet J.
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2003; 35:170-75.
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ACCEPTED MANUSCRIPT Score 0 1 2 3
Quality of sedation Unsatisfactory sedation, minimal or no signs of sedation Mild sedation with head drop slightly lowered Moderate sedation with head lowered, mild ataxia Marked, profound sedation and ataxia
0 1 2
Degree of muscle relaxation Good: complete relaxation, no resistance to limb manipulation Acceptable: muscular rigidity Poor: spontaneous motor activity, struggling during manipulation
1 2 3 4 5
Degree of analgesia Kicking Distinct limb movement Reaction during skin incision and/or clamping of the spermatic cord Minimal reaction during skin incision and/or clamping of the spermatic cord No reaction
A 1 2 3 4 B 1 2 3 C 1 2 3 D 1 2 3 4 E 1 2 3
Quality of recovery Overall attitude Calm Calme/determined Confused, dizzy Frantic Move to sternal Smooth, methodical Fighting mat, but controlled Crashing, flopping over Sternal phase An organised pause Nonexistant Multiple, with struggle Move to stand Methodical An organised scramble Used walls for support Ricocheting off walls Strength Near full Mildly rubbery Dog-sitting before standing
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0 1
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Quality of induction anesthesia Poor: the horse was induced with considerable movement and/or excitement; the horse may have made subsequent attempts to stand or any other situation that could have resulted in injury Fair: the recumbency achieved, the horse fell without relaxation of limbs or with a strong forward or backward movement Good: smooth induction, but horse showed head or limb twitching after induction or a tendency to walk forward or backwards after induction agent was administered Excellent: smooth induction, no muscle twitching. Absent forward or backwards movements
ACCEPTED MANUSCRIPT Repeated attempts due to weakness No. attempts to stand (No. = score) Balance and coordination Solid Moderate ‘dancing’ Reflex saves Careening Falls back down Knuckling None Hindlimbs only All four limbs
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4 F G 1 2 3 4 5 H 1 2 3
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TABLE 1: Scoring system applied for evaluation of the quality of sedation and induction, degree of muscle relaxation and analgesia. The sedation score was modified from Kloppel and Leece (2011).
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The quality of induction and the degree of analgesia were graded using a score previously described by Marntell and colleagues (2006). The degree of muscle relaxation was scored using a scale described by Rossetti and colleagues (2008). The recovery score was grade using a scale proposed
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by Valverde et al (2005).
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Induction score (0-3) 3 (1-3)
Degree of muscle relaxation (0-2) 0 (0-2)
Degree of analgesia (1-5) 5 (2-5)
Induction time (sec)
Time to sternal recumbency (min) 59 (52-97)
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Time to recumbency (sec) 47 (35-65)
47 (35-65)
Time to standing (min) 64 (56-99)
Recovery score (1-6) 1 (1-4)
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Sedation score (0-3) Median 3 Range (2-3)
Table 2: Sedation score, time to recumbency, induction score, degree of muscle relaxation, degree of analgesia, time sternal recumbency, time to
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standing and recovery score in 10 horses undergoing field anaesthesia for orchiectomy. Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1)
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intravenously. At the end of the surgery horses received medetomidine (2 µg kg-1) intravenously. Data are reported as median and range.
ACCEPTED MANUSCRIPT Time after induction (min)
HR (beats/min) fR (breath/min)
Tbaseline
5
10
15
20
25
30
40 (32-52)
30.1 ± 3.8* 11.9 ± 6.5 92.9 ± 4.6
30.3 ± 4.0* 12.0 ± 6.4 94.0 ± 1.8
30.7 ± 3.5* 10.5 ± 14.5 94.3 ± 3.7
28.6 ± 4.0* 15.5 ± 7.9 92.8 ± 5.1
29.7 ± 4.8* 16.3 ± 6.5 93.3 ± 4.8
30.9 ± 4.6* 17.6 ± 6.9 94.0 ± 3.5
16.6 ± 4.8
SpO2 (%)
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Variables
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Table 3: Heart rate (HR), respiratory rate (fR) and arterial oxygen saturation (SpO2) in 10 horses undergoing field anaesthesia for orchiectomy. Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with
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tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1) intravenously. At the end of the surgery horses
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received medetomidine (2 µg kg-1) intravenously. Data are reported as median and range.
Tbase T15 T30 pH 7.4 7.4 7.4 HCO3 28.6 ± 2.4 28.5 ± 1.7 29.1 ± 2.0 PaCO2 mmHg 47.6 ± 5.6 47.9 ± 3.0 48.2 ± 4.4 PaO2 mmHg 103.4 ± 35.5 88.8 ± 28.2 84.1 ± 14.7 SO2 (%) 92.7 ± 6.2 93.9 ± 2.3 94.3 ± 3.3 Hb (g/dL) 11.4 ± 2.0 11.1 ± 3.3 10.5 ± 3.1 Table 4- Blood gas values in 10 horses undergoing field anaesthesia for orchiectomy.
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Horses received acepromazine (0.03 mg kg-1) intramuscularly and medetomidine (8 µg kg-1) intravenously and anaesthesia was induced with tiletamine (0.7 mg kg-1) and zolazepam (mg kg-1) intravenously. At the end of the surgery horses received
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medetomidine (2 µg kg-1) intravenously. Data are reported as median and standard deviation.
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Samples were collected before sedation (Tbase), and 15 (T15) and 30 (T30) minutes after medetomidine administration.
ACCEPTED MANUSCRIPT Highlights: In equine field practice, short to medium-term anaesthesia is commonly required for minor surgical procedures
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In laterally recumbent horses anaesthetized under field conditions, hypoxemia is the most relevant side effect
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In the present study, tiletamine/zolazepam association produced a good quality anaesthesia
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The anaesthesia and analgesia obtained with this protocol was good
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ACCEPTED MANUSCRIPT Ethical animal research
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The study was approved by Bologna University Ethics and Welfare Committee. Owner consent was obtained in all cases.
ACCEPTED MANUSCRIPT Authors’ declaration of interests
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No competing interests have been declared.