Injectable Anesthesia in South American Camelids
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INJECTABLE ANESTHESIA IN SOUTH AMERICAN CAMELIDS Thomas Riebold DVM, Diplomate ACVAA Veterinary Teaching Hospital College of Veterinary Medicine Oregon State University Corvallis, Oregon 97331 INTRODUCTION Interest in llamas, and more recently in alpacas, as pets and as breeding and pack animals has led to increased demand for veterinary services for them. While they have some unique species characteristics regarding anesthesia, many of the principles and techniques used in food animal and equine anesthesia also apply to South American camelids. Except for differences in size, anesthetic management of alpacas and llamas is similar. Much like there are species differences between cattle, sheep, and goats in their response to xylazine, it does appear that alpacas require higher doses of sedatives, approximately 10-20%, to obtain the same response that lower doses of sedatives would obtain in llamas. PREANESTHETIC CONSIDERATIONS Consideration for preanesthetic preparation includes fasting, assessment of hematologic and blood chemistry values, venous catheterization, and estimation of bodyweight. The camelid has a stomach divided into three compartments. Therefore, potential complications similar to those of domestic ruminants, regurgitation and aspiration pneumonia, exist during anesthesia. Abdominal tympany as it occurs in anesthetized domestic ruminants does not appear to occur in anesthetized camelids. It is recommended that the animals be fasted 12-18 hours and deprived of water for 8-12 hours. In nonelective cases, this is often not possible and precautions should be taken to avoid aspiration of gastric fluid and ingesta. Fasting neonatal camelids is not advisable because hypoglycemia may result. As in other species, hematologic and blood chemistry values are determined before anesthesia. Results should be compared to reference values. Venipuncture and venous catheterization are often performed in camelids. Physical restraint during venipuncture or catheterization varies and can consist of a handler holding the camelid's halter, and if the camelid is fractious, grasping an ear; or it can involve use of restraining chutes designed specifically for camelids. Bending the neck excessively to either side seems to hinder venipuncture and catheter placement and increase the likelihood of entering the carotid artery. Local anesthesia at the catheterization site is recommended for catheter placement. The jugular vein is formed rostrally by the union of the linguofacial vein ventrally and maxillary vein dorsally and in that aspect is comparable to the external jugular vein of domestic mammals. However, rather than taking a superficial course in the neck, the vein is directed deeply in its caudal course for most of its length and is contained in the carotid sheath with the common carotid artery and vagosympathetic nerve trunk in a relationship similar to the internal jugular vein of horses and domestic ruminants. Most of the jugular vein lies deep to the sternomandibularis and brachiocephalicus muscles, ventral to cervical vertebral transverse processes. Beginning at a point about 15 cm caudal to the ramus of the mandible, the rostral course of the jugular vein is separated from the carotid artery by the omohyoideus muscle. The origin of the jugular vein is located at the intersection of a line drawn caudally along the ventral aspect of the body of the mandible and another line connecting the base of the ear and the lateral aspect of the cervical transverse processes. Venipuncture or catheterization can be performed at the bifurcation of the jugular vein or at any point caudal to it. Because of the close proximity of the carotid artery to the jugular vein, one must ascertain that the vein has been catheterized and not the artery before injecting any medication. Camelids have a round neck without a distinct jugular groove. The location of the jugular vein can be approximated by placing the four fingers of one's hand at the dorsal midline of the neck and pressing the thumb against the cervical vertebrae. After occlusion of the vessel, one will usually be unable to see the jugular vein distend; however, the vein can be palpated or balloted particularly rostrally and more easily in females and altered males because their skin is thinner. On occasion, one will be able to see the jugular vein of crias and juvenile camelids distend. Sixteen gauge catheters are appropriate for adult camelids and 18-20 gauge catheters for smaller camelids. Camelids can have 4-5 jugular venous valves that prevent flow of venous blood into the head when the head is lowered during grazing. Contact of the catheter tip with jugular venous valves while threading it may prevent successful catheterization; a site caudal to the point where the valve was contacted should be used. Administration of small volumes of drugs can also be made through an ear vein of tractable camelids without too much of a vigorous response from the animal. Use of small gauge needles (25 ga) is recommended. Clipping the area is helpful to improve visibility of the vessel. The vessels are small and the back wall of the vessel is often flattened by the auricular cartilage making the lumen smaller than one would expect. If one wishes to place a catheter in this vessel, it is useful to block the area with lidocaine at the base of the ear. Injection in the caudal auricular artery must be avoided. Injection of drug preparations with pH values widely different from physiological pH, for example, phenylbutazone, must be avoided to prevent thrombophlebitis and risk of ear slough. Finally, bodyweight of the camelid must be determined either by weighing the animal or estimating its weight so that accurate drug administration is possible. It is easy to overestimate bodyweight because camelids, particularly llamas, are fairly tall animals and have a long haircoat that obscures their body type. Adult male llamas usually weigh from 125-160 kg although occasional males can exceed 180 kg. Adult female llamas usually weigh from 100-150 kg but occasional females will also exceed 180 kg. Adult male alpacas usually weigh from 55-80 kg and adult female alpacas usually weigh from 45-70 kg. Bodyweight of crias and small juveniles may be estimated by lifting the individual or a bathroom scale can be used to determine weight by weighing an individual while holding the camelid and without it. 2 SEDATION/RESTRAINT Although acepromazine is not commonly used in llamas and alpacas, it has been used at 0.03 mg/kg. Acepromazine should be expected to produce actions similar to those produced in domestic ruminants. Recumbency usually does not occur. Acepromazine and other phenothiazine derivative tranquilizers are contraindicated in anemic, cachexic or debilitated animals and animals with compromised cardiovascular status. Xylazine is often used to provide sedation or, in higher doses, restraint. Although complete data are not available on the cardiovascular and respiratory effects of xylazine in camelids, the agent causes bradycardia as it does in other species and probably causes mild hypertension or has little effect initially on blood pressure followed by mild hypotension. The degree of sedation or restraint that results depends on the amount given and the animal's temperament. Poorly trained animals or berserk males tend to be less responsive and ill or debilitated camelids are more responsive to sedatives. Low doses (0.1 mg/kg IV or 0.15-0.2 mg/kg IM, llamas; 0.015 mg/kg IV, 0.2-0.3 mg/kg IM, alpacas) provide sedation without recumbency. Butorphanol (0.07-0.1 mg/kg IV or IM) can also be used to provide sedation and analgesia in camelids. While butorphanol does provide sedation, it also causes some degree of dysphoria in camelids yielding sedation that is qualitatively somewhat less than that usually obtained with tranquilizers and sedatives. The animals usually remain standing but may show slight agitation. Higher doses of xylazine will cause recumbency and light planes of general anesthesia. Xylazine, 0.3 mg/kg IV (llamas), 0.4 mg/kg IV (alpacas), usually produces 20 to 30 minutes of recumbency in llamas. Xylazine can also be given intramuscularly at 0.44-0.66 mg/kg (llamas) or at 0.66-0.88 mg/kg (alpacas) to produce recumbency. Higher doses of xylazine, 0.5 mg/kg IV in llamas, can provide sufficient sedation and restraint to allow tracheal intubation. Even though intubation may be possible, muscle relaxation is poor and intubation can be difficult. In a limited number of llamas, detomidine in doses as high as 40 ìg/kg IV provided mild sedation but would not provide restraint in llamas. The animals would lie down following detomidine administration but would arise as soon as a handler approached. Medetomidine has recently been evaluated for use as a sedative/restraint agent in llamas. Doses as low as 10 ìg/kg IM give brief periods of standing sedation (approximately 35 minutes). Onset of sedation is approximately 10-15 minutes. Llamas will not always assume sternal recumbency and, if they do so, duration is brief (5-10 minutes). Analgesia is not present. When medetomidine is given at 20 ìg/kg IM sedation is more profound and lasts approximately 60 minutes. Onset of sedation is approximately 10-15 minutes. Llamas will assume either sternal or lateral recumbency. Analgesia is present about 30 minutes following injection and lasts approximately 30 minutes. When medetomidine is given at 30 ìg/kg IM onset of sedation is within 7 minutes and sedation is more profound. Duration of recumbency approaches two hours. Llamas will assume either sternal or lateral recumbency. Analgesia is present about 15 minutes following injection and lasts 3 Agent Dose Duration Comment Butorphanol 0.07 - 0.1 mg/kg IM 30 - 45 minutes Provides standing sedation without recumbency Xylazine 0.1 mg/kg IV 30 - 45 minutes Provides standing sedation without recumbency. Can be (llamas) 0.15-0.2 mg/kg IM reversed with atipamezole (30 ìg/kg IV), tolazoline (1.0 mg/kg IV), or yohimbine (0.12 mg/kg IV).