Chapter 11 Objectives

Describe the main physiologic and anatomic differences that influence anesthetic management of ruminants, camelids, and swine.

Ruminants The main anesthetic concerns in ruminants result from their unique digestive anatomy and physiology. Ruminants constantly produce large volumes of saliva compared with other species, and this is generally not inhibited by general anesthesia. They are thus prone to aspiration if the airway is not protected. Additionally, regurgitation of rumen contents (known as regurgitus) can occur at any stage of general anesthesia, most commonly during light or deep planes. Fermentation in the rumen is only slightly decreased by general anesthesia, thus ruminants are predisposed to bloat, because they cannot eructate when they are unconscious. Additionally, ruminants present for general anesthesia less frequently than small animals or horses do, so it takes longer to gain anesthetic experience. There are several reasons for this. Due to their relatively calm nature, ruminants require general anesthesia for relatively few procedures. Many surgeries can be conducted using local or regional anesthetic techniques in conjunction with physical restraint. Consideration must also be given to drug withdrawal times when dealing with animals that produce milk or meat for human consumption. Finally, administration of general anesthesia to production animals is often uneconomical. Ruminant patients range in size from a few kilograms (lambs and kids) to over 1000 kg (adult bull). Thus, as with horses, specialized tilt tables, head gates, hoists and transporters may be required to allow the veterinarian to perform surgery or procedures such as hoof-trimming safely without injury to the animal or personnel. Equipment suitable for anesthetizing small animal patients is commonly used for smaller patients (sheep, goats, calves). However, if young cattle >150 kg in body weight and adult cattle are to undergo general anesthesia, the anesthetist must have access to a large animal anesthetic machine and be familiar with its operation as well as that of related equipment and monitors. Camelid General anesthesia of camelids is very similar to that of small ruminants because they have a similar digestive system. Although camelids are not true ruminants, the first stomach compartment plays a similar role to the rumen. Camelids produce copious saliva even when anesthetized and have the ability to chew cud, thus it is common to find food material in the oral cavity at induction. Unlike ruminants, anesthetized camelids are prone to developing nasal congestion when placed in lateral or dorsal recumbency. Like horses, camelids are obligate nasal breathers and may also develop upper airway obstruction during recovery. Anesthetic management therefore tends to focus on these specific concerns in addition to the general concerns for anesthetizing any veterinary patient. Intravenous catheters are commonly placed in the jugular or cephalic veins. The skin on the neck of camelids is typically thicker and much tighter than that of small ruminants. This can make it comparatively more difficult to place an IV catheter in the jugular vein successfully, and a little easier to mistake the carotid artery for the jugular vein, which may result in inadvertent carotid puncture. Swine Pigs are challenging patients to restrain, sedate, and anesthetize because of unique characteristics in this species that make physical examination, sedation, IV catheterization, and intubation much more difficult than in the species discussed so far.

Explain how to intubate an adult cow, a small ruminant, calf or camelid, and a pig.

Adult Cattle Adult cattle are intubated manually using a blind technique. A speculum or mouth gag is placed which prevents the cow from closing its mouth. This protects the anesthetist's arm and hand from being damaged if the cow should become light enough to chew. The anesthetist then inserts his or her nondominant hand into the mouth up to the larynx, holding (and protecting) the endotracheal tube in his or her hand. The dominant hand is used to direct the tube. Once the anesthetist's fingers are at the level of the larynx, the anesthetist palpates the epiglottis, reflects it forward if necessary, and directs the end of the endotracheal tube into the trachea, advancing it with his or her dominant hand. Extending the head and neck of the cow, while sometimes challenging due to its weight, is often helpful while passing the tube. Upon successful placement, the endotracheal cuff is inflated. The tube is then secured by tying it to the halter or around the muzzle in a similar manner to that used for a dog. Intubation Procedure for Adult Cattle Ruminants are generally intubated while in sternal recumbency. 1. Place a mouth speculum or gag. 2. Grasp the tongue and pull it forward. 3. Extend the head and neck. 4. Hold the tube at the patient end and cover the cuff with the nondominant hand. 5. Holding the tube in this manner, extend the nondominant arm into the mouth and advance to the larynx. Use the dominant hand to assist with advancement of the machine end of the tube. 6. Palpate the epiglottis and laryngeal opening with one or two fingers of the nondominant hand. 7. Pass the tube into the larynx, using the nondominant hand to push the end of the tube into the airway, and the dominant hand to advance the tube. 8. Check to ensure the tube is in the trachea by feeling air pass during exhalation or when an assistant presses down on the patient's chest. 9. A small volume of air may be placed in the cuff (20 to 60 mL) before hoisting or positioning the cow. 10. Secure the tube to the halter or to the muzzle. 11. After the cow has been positioned on the surgery table, connect the endotracheal tube to the anesthetic breathing system and allow the patient to breathe 100% oxygen. 12. Check the tube for leaks. 13. Turn on the anesthetic vaporizer, and adjust the appropriate level. 14. Commence regular monitoring. Small Ruminants and Calves Intubation in these patients is accomplished as for small animal patients. The oral opening is small in these patients compared to the distance between the mouth and larynx, so visualization of the airway can be challenging. Additionally, the caudal half of the tongue is thickened which further obstructs the anesthetist's view. Attempting to pass the endotracheal tube alone typically completely obstructs the view, making successful placement extremely challenging, and more a matter of luck than skill. Therefore using a narrow stylette that protrudes beyond the end of the tube allows better visualization of the larynx. With the head extended by an assistant, the anesthetist places a laryngoscope to visualize the larynx. It often helps to grasp the tongue with a gauze sponge and gently pull it forward. The anesthetist then passes the stylette into the airway, taking care not to cause injury to the larynx or trachea. The endotracheal tube can then be passed over the stylette and into the larynx (Figure 11-3). The cuff is inflated as for small animal intubation (see Chapter 9). Endotracheal Intubation Porcine Endotracheal intubation of swine is particularly challenging because of poor visibility, resulting from the limited extent to which the mouth can be opened, a long soft palate, the relatively narrow dental arcade, and the anatomy of the larynx and proximal trachea. A ventral laryngeal diverticulum is present into which the tube can easily be misdirected, and the laryngotracheal junction is at an angle rather than being straight as in other domestic species. Finally, the larynx of a pig is sensitive and may spasm when stimulated, making intubation even harder. The novice anesthetist should seek assistance from an experienced person when intubating a pig, as it is easy to damage the larynx by forcing the tube. There are several methods of intubating pigs. The pig may be placed in either in sternal or dorsal recumbency. Similarly to small ruminants, a straight stylette is placed within the tube such that several inches of it extend beyond the bevel of the tube. Using a laryngoscope to visualize the airway, the stylette is passed into the larynx, bypassing the diverticulum. The tube can then be gently threaded over the stylette into the trachea. Care must be taken with the stylette to avoid damage to the larynx and trachea (Figure 11-12). Alternatively, a stylette with a 20- to 30-degree curve in it is placed in the tube, ensuring that it does not extend beyond the end of the tube. The tube is inserted into the larynx with the convex surface against the palate. Once the tube is placed in the larynx, the tube and stylette are rotated 180 degrees and advanced into the trachea. Patience should be exercised, and if the pig becomes light during intubation, further attempts at intubation should be halted until IV or inhalant drugs have been administered and an appropriate depth of anesthesia for intubation is achieved.

Describe the clinical signs of porcine stress syndrome.

Also known as malignant hyperthermia, porcine stress syndrome has been associated with anesthesia, particularly inhalant anesthetics. This metabolic condition is due to a mutation in one of the genes that controls calcium metabolism in the muscle. Symptoms include muscle rigidity, a rapid rise in temperature, hypercapnia, hyperkalaemia, and death. Treatment includes immediate termination of all anesthetic drugs, delivery of oxygen at high flow rates, and treatment with dantrolene.

Explain how to position a camelid for recovery.

Care should be taken with the long, flexible neck during induction, positioning, and recovery to prevent injury. The eyes of camelids are large and prominent, and should be protected during movement of the patient during induction, positioning, and recovery. As with ruminants, the head should be positioned to allow drainage of saliva and regurgitus by placing the mouth lower than the pharynx. Camelids should be placed in sternal recumbency for recovery from general anesthesia. The head and neck should be held upright in a normal position to promote venous drainage of any upper airway congestion that may have developed during the procedure. If breathing seems labored after extubation, or if stridor is present, oxygen can be delivered by facemask. If dyspnea develops, nasal tubes can be placed by gently advancing a small endotracheal tube into the ventral meatus of one or both nostrils until passage of air is felt through them. If placement of nasopharyngeal tubes does not alleviate the obstruction, the attending veterinarian should be notified immediately. Complete airway obstruction is an emergency, and may require reintubation of the trachea, or a tracheostomy. Like ruminants, camelids tend to remain calm, and consequently rarely require sedation in the recovery period.

Explain how to prepare a ruminant, camelid, or porcine patient for anesthesia.

Patient Preparation Ruminant 1. Assess, prepare, and weigh the patient. 2. Prepare equipment for and place an intravenous (IV) catheter (clippers, local anesthetic, antiseptic scrub, catheters, tape, normal saline, suture material, catheter cap, and/or extension line with threeway stopcock). Catheter placement in large or aggressive cattle may require restraint in a chute with a head gate. 3. Determine the protocol (anesthetic agents, including dosages, routes, and sequence of administration). 4. Calculate the volume of each agent to give, including fluid administration rates (preanesthetic, induction, maintenance, and analgesic agents). 5. Review the oxygen flow rates. 6. Prepare the equipment required to administer drugs (syringes, needles, agents, reversal agents, emergency cart, controlled substance log). 7. Prepare fluid administration equipment (fluids, administration/extension set, syringe pump, tape, normal saline). 8. Prepare equipment for endotracheal intubation. Have suction equipment assembled and turned on for small ruminants and camelids. Remove jewelry, watch, and ensure fingernails are trimmed short for digital intubation of adult cattle. 9. Prepare monitoring equipment, including arterial catheterization materials, anesthesia record, monitors, and probes. 10. Assemble and test the anesthetic machine and ventilator. Additionally, the anesthetist should be familiar with operation of equipment such as surgical tables, transporters, head gates, and hoists that will be used during the anesthetic episode. It is essential to ensure that ruminants have been adequately fasted before anesthesia. Fasting reduces the size of the rumen and also decreases microbial activity. This in turn decreases gas production during anesthesia. Normally ruminants eructate to expel the gas from the rumen, however under anesthesia this does not happen, and this can lead to bloating. A bloated rumen can put pressure on the diaphragm and large blood vessels (aorta, caudal vena cava) in the abdomen, resulting in respiratory as well as circulatory compromise. Once an anesthetized ruminant develops severe bloat it can be very difficult to treat and may lead to death if it goes unnoticed or untreated. Bloat often goes unrecognized when a patient is small and covered by surgical drapes. Clinical signs include development of a distended, tight abdomen, decreased blood pressure, increased heart rate, and decreased ventilation. Patient Preparation Camelid Camelids are prepared for anesthesia in the same manner as small ruminants. Intravenous catheters are commonly placed in the jugular or cephalic veins. The skin on the neck of camelids is typically thicker and much tighter than that of small ruminants. This can make it comparatively more difficult to place an IV catheter in the jugular vein successfully, and a little easier to mistake the carotid artery for the jugular vein, which may result in inadvertent carotid puncture. If a hematoma forms as a result of unsuccessful venipuncture of the neck, the tight skin tends to compress it inwards, leading to the possibility that the trachea will be compressed and partially obstructed. In the event that a hematoma develops, it may be prudent to postpone a nonemergency procedure for 24 hours to allow some resolution of the hematoma. Patient Preparation Porcine In most swine, physical examination is impossible beyond general observation of the animal, assessment of respiratory rate and character, and detection of obvious problems such as nasal discharge. Conscious pigs typically squeal in protest when restrained, making procedures such as thoracic auscultation impossible. The anesthetist must often rely on patient history to determine health status. Pigs also do not have readily accessible peripheral veins or arteries, making further investigation of cardiovascular status and blood sample collection very difficult or impossible without causing extreme stress to the animal, and the handler.

Select an anesthetic protocol for an ASA PS1 or PS2 adult cow, small ruminant, camelid, or pig.

Selecting a Protocol Ruminants A suitable protocol takes into account the minimum patient database, the patient's physical status class, and the type and duration of procedure to be performed. Regardless of the protocol, the correct drugs and amounts must be prepared. Ill, geriatric, pediatric, or otherwise compromised patients (physical status class P3 to P5) require use of modified protocols based on the patient's primary condition. Management of these cases can be quite challenging and requires customization of the anesthetic protocol by the attending veterinarian. Premedication/Sedative Protocols for Physical Status Class (PSC) PS1 and PS2 Ruminants and Camelids ∗Protocols for Light-Moderate Sedation: 1. IV acepromazine: Acepromazine 0.01 to 0.03 mg/kg IV (may increase regurgitation) 2. IV/IM xylazine: Xylazine 0.01 to 0.05 mg/kg IV or IM (unlikely to cause recumbency) 3. IV detomidine: Detomidine 0.005 to 0.02 mg/kg IV †Protocols for Moderate-Deep Sedation (for minor procedures such as radiography or wound assessment) or for Premedication: 1. IV acepromazine: Acepromazine 0.03 to 0.05 mg/kg IV 2. IV/IM xylazine: Xylazine 0.05 to 0.1 mg/kg IV or 0.05 to 0.2 mg/kg IM (likely to cause recumbency and potentially light anesthesia) 3. IV detomidine: Detomidine 0.01 to 0.03 mg/kg IV 4. IV midazolam-butorphanol: Midazolam 0.1 mg/kg and butorphanol 0.1 to 0.2 mg/kg IV (may produce ataxia, so recommended for small ruminants/camelids or restrained cattle) Intravenous Induction Protocols for PSC PS1 and PS2 Ruminants and Camelids 1. IV ketamine-diazepam: Ketamine 2.5 mg/kg IV and diazepam∗ 0.12 mg/kg IV mixed in the same syringe. (This is equivalent to 1 mL of the mixture per 20 kg of body weight. Note the difference from the small animal dosage.) This combination is used most commonly in small ruminants and camelids. 2. IV "double drip": "Double drip" IV to effect (approximately 1 to 2 mL/kg). "Double drip" can be made by adding 500 mg ketamine to a 500 mL bag of 5% guaifenesin. Each milliliter of "double drip" therefore contains 1 mg ketamine and 50 mg guaifenesin. 3. IV telazol: Telazol 1 to 4 mg/kg IV (use a lower dose after premedication with xylazine). 4. IV propofol: Propofol 2 to 4 mg/kg IV (for small ruminants/camelids only; not economical for adult cattle). Intravenous Induction in Adult Cattle Induction of anesthesia in adult cattle is similar to that in horses in that the goal is to achieve lateral recumbency without excitement or injury to the patient or personnel. In order to do this, the induction agent is given as a rapid IV bolus to PS1 and PS2 cows. The only induction agent that is given "to effect" (see Procedure 9-3 in Chapter 9) is "double drip." • Ketamine-diazepam and ketamine-midazolam mixtures: After checking to make sure that the IV catheter is patent and still in the jugular vein, the entire syringeful of the calculated dose of drugs is rapidly injected into the catheter or extension set, then the catheter flushed using heparinized saline. • Double drip (guaifenesin 50 mg/mL and ketamine 1 mg/mL): A bag of double drip with an IV administration set attached is placed in a pressure sleeve, which is inflated up to 300 mmHg pressure. The administration set is connected to the IV catheter or extension set. After checking to make sure that the IV catheter is patent and still in the jugular vein the double drip is administered under pressure to effect. Approximately 1 to 2 mL/kg will produce signs of ataxia (swaying) followed by recumbency. If intubation is not possible, a further 1 to 2 mL/kg may be administered more slowly, or a bolus of ketamine 1 mg/kg IV may be given. Selecting a Protocol Ruminants Camelids are generally easy to handle, and the protocols used in small ruminants are recommended. Aggressive camelids may be quite resentful of restraint for examination or venipuncture, and may require sedation. Premedication/Sedative Combinations for Aggressive PS1 and PS2 Camelids 1. IM xylazine-butorphanol: Xylazine 0.2 to 0.5 mg/kg and butorphanol 0.1 to 0.2 mg/kg IM 2. ∗IM ketamine-xylazine-butorphanol: Ketamine 3 to 5 mg/kg, xylazine 0.2 to 0.5 mg/kg, and butorphanol 0.1 to 0.2 mg/kg mixed in a syringe and administered intramuscularly Selecting a Protocol Porcine Sedative drugs are most commonly administered by IM injection in pigs owing to the lack of easily accessible peripheral veins, but the presence of a thick layer of subcutaneous fat makes IM administration of drugs difficult without the use of needles that are at least 1.5 inches long. The most accessible site for IM injection is in the muscles of the neck caudal to the ear and at least 3 to 5 cm lateral to the dorsal midline. Swine are generally considered to be the most resistant to sedative drugs of the domestic species, and many protocols for IM sedation, premedication, or total injectable anesthesia include a tranquilizer or sedative, an opioid, and a dissociative. Various combinations of drugs have been used to sedate swine. Generally, drug combinations that include a dissociative produce more predictable and heavier sedation that, in some pigs, may produce anesthesia for short surgical and nonsurgical procedures. A combination that is widely used to produce heavy sedation or anesthesia is Telazol, ketamine, and xylazine, or TKX. Premedication/Sedative Protocols for PSC PS1 and PS2 Swine Protocols for Light-Moderate Sedation 1. IM acepromazine-butorphanol: Acepromazine 0.04 to 0.09 mg/kg and butorphanol 0.05 to 0.1 mg/kg IM∗ 2. IM dexmedetomidine-butorphanol: Dexmedetomidine 0.02 to 0.03 mg/kg and butorphanol 0.05 to 0.1 mg/kg IM∗ Protocols for Moderate-Deep Sedation 1. IM "TKX": TKX administered IM at a dosage of 1 mL/50 kg to a maximum of 3 mL 2. IM dexmedetomidine-ketamine-butorphanol: Dexmedetomidine 0.02 mg/kg, ketamine 5 mg/kg, and butorphanol 0.2 mg/kg IM∗ 3. IM romifidine-ketamine-butorphanol: Romifidine 0.12 mg/kg, ketamine 8 mg/kg, and butorphanol 0.1 mg/kg IM How to Prepare and Administer TKX (Telazol−Ketamine−Xylazine) to Swine 1. Reconstitute a bottle of Telazol with 2.5 mL of 100 mg/mL ketamine and 2.5 mL of 100 mg/mL xylazine. 2. The final mixture of TKX contains the following drugs and concentrations: Tiletamine 50 mg/mL Zolazepam 50 mg/mL Ketamine 50 mg/mL Xylazine 50 mg/mL 3. Administer TKX at 1 mL/50 kg IM up to a maximum of 3 mL.

Explain the unique concerns and challenges when anesthetizing pigs.

The eyes of pigs are very small and sunken, and do not provide reliable information about depth of anesthesia. Readiness for intubation is often best assessed by seeing whether the mouth can be opened without resistance. Endotracheal intubation of swine is particularly challenging because of poor visibility, resulting from the limited extent to which the mouth can be opened, a long soft palate, the relatively narrow dental arcade, and the anatomy of the larynx and proximal trachea. A ventral laryngeal diverticulum is present into which the tube can easily be misdirected, and the laryngotracheal junction is at an angle rather than being straight as in other domestic species. Finally, the larynx of a pig is sensitive and may spasm when stimulated, making intubation even harder. Pigs can be challenging to monitor effectively because they have few palpable peripheral arteries, and their cone-shaped legs make the use of blood pressure cuffs, which are designed for the more cylindrical arms of people, difficult.

Explain how to position a ruminant for recovery.

Unlike horses, ruminants are generally content to lie in sternal recumbency following anesthesia. The development of complications from anesthetic recovery is generally limited to the residual effects of bloat. Ruminants rarely develop nasal edema during anesthesia and usually do not require nasal intubation.

Explain the importance of proper positioning of anesthetized ruminants and camelids.

• All ruminants should be positioned for surgery with the mouth lower than the pharynx to allow drainage of saliva and any regurgitated material from the mouth, preventing buildup in the pharynx, which could lead to aspiration during recovery following extubation. • Ruminants, even large cattle, are not predisposed to developing myopathy or neuropathy, unlike horses, however appropriate physical support and padding during anesthesia is pruden