Veterinary Anaesthesia and Analgesia, 2012, 39, 111–118
doi:10.1111/j.1467-2995.2011.00671.x
CASE REPORT
Medetomidine-ketamine-isoflurane anaesthesia in pygmy hippopotami (Choeropsis liberiensis) – a case series Tim Bouts*, Robert Hermes , Frank Gasthuysà, Joseph Saragusty , Polly Taylor§, Andrew Routh* & Thomas B Hildebrandt *Zoological Society London, ZSL Whipsnade Zoo, Veterinary Department, Whipsnade, Bedfordshire, UK Department of Reproduction Management, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany àDepartment of Surgery and Anaesthesiology, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium §Taylor Monroe, Ely, Cambridgeshire, UK
Correspondence : Tim Bouts, Zoological Society London, ZSL Whipsnade Zoo, Veterinary Department, Whipsnade, Bedfordshire, LU6 1DP, UK. E-mail:
[email protected]
Abstract History Medical knowledge of pygmy hippopotami is limited. Anaesthesia has been considered a challenge because of the anatomy, semi-aquatic life style and aggressive behaviour. Polycystic kidney disease (PKD) has been described and can contribute to active kidney disease potentially affecting anaesthesia. Physical examination and Management Fourteen pygmy hippopotami were anaesthetized for general health assessment and reproductive procedures. Animals (estimated bodyweight 250 kg) were darted intramuscularly with 0.08 mg kg)1 medetomidine and 1.2 mg kg)1 ketamine. After endotracheal intubation, anaesthesia was maintained with isoflurane delivered either by circle system (100% oxygen) or by Triservice apparatus (air or air/ oxygen admixture). Heart rate (HR) respiratory rate (fR), oxygen saturation (SpO2) and end tidal CO2 were recorded at 5-minute intervals. Atipamezole was administered intramuscularly (0.4 mg kg)1) at the end of the procedure. Statistical analysis was performed using ANOVA (p < 0.05). Most animals rapidly became recumbent although five hippopotami needed additional drugs to assure acceptable immobilization. There were no statistical differences in mean HR between animals with or without PKD (PKD: 34 ± 8 beats minutes)1; no
PKD: 33 ± 6 beats minutes)1), fR (PKD: 15 ± 7 breaths minutes)1; no PKD; 12 ± 5 breaths minutes)1) and end tidal CO2 (PKD: 7.1 ± 1.3 kPa; no PKD: 7.8 ± 1.4 kPa). SpO2 was higher in animals receiving 100% oxygen or air with oxygen (92 ± 8% and 91 ± 9% respectively) compared with animals receiving air only (77 ± 5%) (p = 0.003). Recovery was uneventful after atipamezole administration. Follow-up There were no apparent adverse effects after anaesthesia during a 24-hour follow-up period. Discussion and conclusions Medetomidine-ketamine-isoflurane induced satisfactory anaesthesia in this species. Incremental induction doses were related to remote injection and the animals’ thick skin. There were no differences in anaesthetic parameters in animals with or without PKD. Supplemental oxygen should be mandatory during anaesthesia in this species. Keywords atipamezole, Hexaprotodon liberiensis, isoflurane, ketamine, medetomidine, Triservice apparatus.
Introduction Medical knowledge about pygmy hippopotami (Choeropsis liberiensis) remains scarce and is mainly 111
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based on post-mortem findings (Raymond et al. 2000; Nees et al. 2009) or individual case reports. A female-biased sex ratio has been reported in captive populations (Zschokke 2002). Polycystic kidney disease (PKD) also occurs in captive populations (Raymond et al. 2000; Nees et al. 2009; Hermes et al. 2010). PKD has been considered to contribute to possibly life threatening renal complications in this species (Raymond et al. 2000; Nees et al. 2009). Most case reports only provide a brief mention of the anaesthetic procedures (Franz et al.1978; Miller & Boever 1983; Flach et al. 1998; Johnston 2002; Bouts et al. 2009). Only three manuscripts have discussed anaesthesia in more detail (Jarofke & Klo¨s 1982; Pearce et al. 1985; Weston et al. 1996). Similarly, only three secondary book references are available (Jarofke 1993; Miller 2003, 2007). Anaesthesia of pygmy hippopotami remains a challenge for zoo and wildlife veterinarians. These animals are extremely territorial and aggressive and are capable of inducing fatal injuries mainly by their elongated canine teeth (Miller 2003). They are considered to be pseudo-ruminants since pygmy hippopotami have two diverticula at the end of the oesophagus lined by papillae, similar to the rumen (Schwarm et al. 2003). Consequently, fasting of at least 24 hours is recommended to reduce pressure of the gut on the diaphragm during recumbency. Since hippopotami head for water when frightened or aroused, anaesthesia should be carried out away from a pool to prevent accidental drowning. Pygmy hippopotami also have a very thick skin; recommended injection sites are either the medial or caudal aspect of the thigh or the area in the neck caudal to the ear (Miller 2003, 2007). In the past, a survey of anaesthetic techniques used in pygmy hippopotami was performed in collaboration with more than 100 zoos (Jarofke & Klo¨s 1982). In summary, all anaesthetic drugs were delivered intramuscularly (IM). Etorphine, either alone or in combination with acepromazine, azaperone, propionylpromazine or xylazine, was the most commonly used agent. Etorphine was successfully antagonized with diprenorphine. However, side effects including salivation, excitation and dog-sit position during induction often were reported with these combinations. Phencyclidine, a potent dissociative anaesthetic agent, was also administered in this species, either with acepromazine or propionylpromazine. Ketamine and xylazine combinations were used only sporadically (Jarofke & Klo¨s 1982). 112
Pearce et al. (1985) reported twenty-one anaesthetic events using different drugs over a 1-year period in a single animal. Etorphine, either alone or combined with acepromazine, together with xylazine induced satisfactory sedation with only minor involuntary leg movements. Intramuscular detomidine or medetomidine mixed with butorphanol has also been described but animals became aroused upon stimulation (Miller 2003, 2007). Midazolam-zolazepam-tiletamine caused mild sedation. Ketamine-butorphanol has been used for induction of anaesthesia but required supplemental drugs (Miller 2003, 2007). A case report mentioned the use of multiple injections of different drugs (atropine, ketamine, butorphanol, detomidine) for induction of anaesthesia in a single pygmy hippopotamus, followed by isoflurane after endotracheal intubation (Weston et al. 1996). Ketamine (1–1.2 mg kg)1) and medetomidine (0.08 mg kg)1) have been used successfully for induction of anaesthesia in pygmy hippopotami. An endotracheal tube was placed and anaesthesia maintained with isoflurane. Dental procedures, general health examinations and a broncho-alveolar lavage were performed with this protocol (Johnston 2002; Bouts et al. 2009). In order to investigate the presence of PKD and infertility problems combined with a distorted sex ratio at birth in this species, it was decided to initiate a health screening protocol in pygmy hippopotami across Europe. Zoos were asked to participate in this health screening which consisted of a full general examination including ultrasound of the reproductive organs and of the kidneys to diagnose PKD. The present paper reports on the efficacy and safety of the combination of medetomidine and ketamine for induction of anaesthesia followed by isoflurane in a larger number of pygmy hippopotami, and describes subsequent antagonism with atipamezole. Furthermore, based on the renal ultrasound findings of the kidneys, a retrospective investigation was carried out to ascertain whether the presence or absence of PKD influenced the speed of onset or recovery from anaesthesia, the parameters measured intra-operatively, or resulted in any delayed adverse effects. Case histories and management Fourteen (eight PKD and six no PKD) pygmy hippopotami (ages 9–40 years; life span in captivity between 35 and 45 years) were anaesthetized for
2011 The Authors. Veterinary Anaesthesia and Analgesia 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 39, 111–118
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routine clinical procedures in six different zoos across Europe. The same anaesthetist performed all anaesthetic procedures, but facilities and equipment differed according to the site. PKD was confirmed if at least one kidney had three or more cysts. The pygmy hippopotami were separated from conspecifics the day before anaesthesia; food was withheld for 24 hours but the animal had free access to a pool up to 12 hours before anaesthesia. Body weights of the animals were not available at the time of the procedures. Based on previous experience (Bouts et al. 2009) and known weights from post-mortem reports, a body weight of 250 kg was used as a standard in all except one animal that was judged visually to be considerably thinner (estimated body weight 185 kg). Medetomidine at 0.08 mg kg)1, (Zalopine, 10 mg mL)1, Orion Pharma, Orion Corporation, Finland) and ketamine at 1.2 mg kg)1, (Ketamine 10%; WDT eG, Germany) were mixed in one syringe and administered into the neck muscles, using a 5 mL compressed air projectile syringe and a CO2 powered rifle (DanInject IM Rifle; Smith GmbH, Germany) using a 40 mm long, 2 mm diameter needle. The anaesthetic doses were based on previous experience in this species by the anaesthetist (Bouts et al. 2009). If the level of immobilization or of anaesthesia was considered to be insufficient either for approaching the animals or for intubation, additional drugs were administered by darting (ketamine and medetomidine) or by manual IM injection (ketamine). Times of the appearance of first signs of sedation (e.g. head bobbing and/or ataxia) after darting and to sternal recumbency were recorded. When animals became unresponsive to external stimuli, including hand clapping and gentle prodding with a wooden pole, they were approached and blindfolded. To facilitate intubation, the mouth was kept open with two ropes placed caudal to the canine teeth of the upper and lower jaw and the larynx was visualized with a laryngoscope with a long (55 cm) blade (Medical Engineering and Development, MI, USA). The trachea was intubated with a rubber 12–14 mm diameter cuffed endotracheal tube (Burtons, UK). Following successful intubation, anaesthesia was maintained with isoflurane (Isoba Vet, Nbl; Essex Pharma GmbH, Germany) either from a non-rebreathing draw-over system (Triservice apparatus (TSA), International Zoo Veterinary Group, UK) with a built-in draw-over Oxford Miniature vaporizer (OMV) calibrated commercially using infrared mass spectrometry for
different isoflurane vaporizer settings and drawover air-flow rates (Lewis 2004) and air (two animals) or a mixture of air and oxygen (eight animals) as carrier gasses; or a standard circle system (four animals) (Burtons) with a Mark 3 ‘Tec’ isoflurane vaporizer (Datex-Ohmeda, UK) and oxygen. Animals anaesthetized with the TSA were supplemented with oxygen when available (n = 8) when SpO2 dropped below 90%. Oxygen supplementation was started with 5 L minute)1, was reviewed every 5 minutes, and the oxygen flow rate was changed as indicated. Concentration of the isoflurane was adjusted according to the clinical signs of depth of anaesthesia (palpebral and corneal reflexes, muscle tone in the jaw and limbs, changes in vital parameters). Heart rate (HR), respiratory rate (fR), end tidal CO2 and oxygen saturation (SpO2) were recorded at 5 minute intervals by means of a combined capnograph and pulse oximeter (Capnocheck II V8402; Smiths Medical, UK). Additionally, venous blood gases (medial saphenous vein) were measured in two animals (I-STAT hand held blood analyzer; Abbott, UK). All animals were positioned in lateral recumbency. The clinical procedures included a general health check and ultrasonography of the kidneys and reproductive organs. In all males a diagnostic electro-ejaculation was carried out (Saragusty et al. 2010). Blood samples were collected for routine haematology and biochemistry either from the sublingual, medial saphenous, cephalic or ventral tail vein. Three animals (circle system), after cannulation of the cephalic or medial saphenous veins, received IV fluid therapy (10 mL kg)1 hour)1, NaCl 0.9%) throughout the procedures. Once the procedure was completed, medetomidine was antagonized with atipamezole (Antisedan; Pfizer Animal Health, UK) given at a dose rate of 0.4 mg kg)1 IM into the neck muscles. As the half life of medetomidine is unknown in pygmy hippopotami, the dose of atipamezole chosen was five times that of the medetomidine dosage in all animals regardless of the duration of the procedure. Times from atipamezole injection to achieving both sternal recumbency and to standing were recorded. Data were analysed with animals divided into two groups according to whether or not animals had PKD. Subsequently all animals were divided into three groups according to the nature of the carrier gasses: air, oxygen/air, and 100% oxygen. Data are presented as mean ± SD.
2011 The Authors. Veterinary Anaesthesia and Analgesia 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 39, 111–118
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Statistical analysis was carried out on SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, USA). Univariate ANOVA was used in each group to assess changes over time in HR, fR, SpO2 and end tidal CO2. Levene’s test combined with a histogram was used to check for homogeneity and normal distribution of the data respectively. Bonferroni correction was applied post hoc. Values of p £ 0.05 were considered statistically significant. Diagnosis and management Remote injection by dart induced brief arousal ( 0.05).
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2011 The Authors. Veterinary Anaesthesia and Analgesia 2011 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 39, 111–118
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was unknown. Oxygen was not available for the remaining two animals. Isoflurane was used in all animals. The settings of the vaporizer were adjusted according to the depth of anaesthesia. Isoflurane was administered for 65 ± 21% of the duration of the procedure (time from intubation to extubation) in males compared to 43 ± 22% in females (p = 0.03); isoflurane vaporizer settings were the same in both sexes (1.7 ± 0.4%). HR, fR and end tidal CO2 remained relatively stable throughout anaesthesia without statistically significant differences (p > 0.05) between PKD and non PKD animals or over time (Table 1). In one animal, HR was consistently
