Anesthetic Management of Specific Procedures

Anesthetic Management of Specific Procedures

Benjamin Newcomer

Veterinary Education, Research, & Outreach Program, Texas A&M/West Texas A&M Universities, Canyon, TX, USA

Selection and implementation of anesthetic protocols in farm animals are largely influenced by the species of animal, the particular procedure to be performed, individual knowledge and experience of the veterinarian with respect to inhalation or injectable anesthesia agents, economics, and the facilities and personnel available for support. The purpose of this chapter is not to present an in‐depth discussion of surgical procedures, as details on the surgical approaches and procedures are well documented in other texts [13]. Rather, this section presents anesthetic techniques utilized routinely for the procedures described. The authors recognize that many alternatives and personal preferences exist for anesthetic management of various conditions in farm animals and ultimate selection of the anesthetic protocol will be dictated by many factors, including clinician preference, logistical constraints, and animal welfare considerations.

Because of the docile nature of ruminant patients and the capability for physical restraint in a chute, most standing surgical procedures in field settings can be performed in cattle using local anesthetics alone or utilizing combinations of chemical restraint with local or regional anesthesia. Chemical restraint can also be utilized for procedures where recumbency is preferred. Although the term “balanced” anesthesia is not often associated with field anesthesia in farm animals, the reality is that most surgical procedures involving ruminants can be accomplished using this method, where combinations of two or more classes of drugs, including sedatives, tranquilizers, analgesics, and local anesthetics, are utilized to provide sedation, analgesia, and muscle relaxation. The advantage of utilizing multiple classes of drugs in an anesthetic plan is safety, as smaller doses of two or more agents are considered safer than the usual large dose of a single agent. Swine, including pot‐bellied pigs, are less tolerant of physical restraint, therefore deep sedation or general anesthesia is often necessary to perform even minor surgical procedures.

For surgical procedures where recumbency is preferred or where a procedure requires an extended period of immobility or high level of analgesia, general anesthesia offers optimal restraint, ability for aseptic surgical conditions, proper handling of tissues, and hemostasis. Location for performing the general anesthesia, positioning of the patient, and preparing for regurgitation, rumen tympany, and salivation are important considerations prior to induction (Chapter 1). The choice of injectable or inhalation maintenance general anesthesia often depends on the availability of gas anesthetic equipment and personal experience. Since depth of anesthesia can be easily and rapidly adjusted with inhalation anesthetics (e.g. isoflurane, sevoflurane, and desflurane) (Chapter 6), inhalation anesthesia is preferred over injectable anesthesia for lengthy procedures or for patients considered higher anesthetic risk because of systemic illness. If general anesthesia is utilized, anesthetic protocols should be individually designed, especially with respect to critically ill patients, neonates, and other animals where anesthetic risk is considered high. Prior to anesthesia, patients should be evaluated by physical examination with or without clinical pathologic examination to assess their risk associated with anesthesia and surgery. Heart defects and pulmonary dysfunction can be identified during careful auscultation of the thorax, and evidence of cardiovascular compromise can be subjectively assessed by mucous membrane color and capillary refill time. Complete blood counts and biochemistry panels should be evaluated in cases where inflammatory disease, electrolyte derangements, or vital organ dysfunction is suspected. Classification of animals by physical status 1–5 has been proposed to aid in determining anesthetic risk, with higher physical status having greater risk of complications associated with anesthesia [4]. Apparently healthy animals undergoing an elective surgical procedure can be classified as physical status 1. For simple elective surgical procedures in young, apparently healthy animals, preoperative laboratory evaluation is not usually necessary. An animal with a slight to moderate systemic disturbance that does not interfere with function is physical status 2, and examples include mild dehydration, obesity, umbilical hernias, poor body condition, and simple fractures. Physical status 3 animals are those with slight to moderate systemic disturbances that do interfere with normal function, and examples include heart defects, severe electrolyte imbalances, oxygen exchange problems such as pneumonia, moderate to severe dehydration, and compound fractures. Physical status 4 animals are those with uncompensated systemic disturbances or life‐threatening conditions where surgical intervention is deemed lifesaving. Finally, physical status 5 animals are those in moribund condition. If at all possible, assessing clinical pathology and stabilizing body systems by provision of fluid and electrolyte therapy are important in physical status 3–5 animals. Packed cell volume and total protein measurements are screening tests which are easily performed and can provide information that can influence preparation for anesthesia and surgery. For physical status 4 and 5 animals, anesthesia and surgery are often performed without the luxury of time and presurgical stabilization. Monitoring of high‐risk patients during anesthesia is important and should continue throughout the recovery phase. Anesthetic deaths can occur during the recovery phase.

9.1 Urogenital Surgery in the Male

9.1.1 Castration

Castration represents one of the most frequent surgical procedures performed in farm animal species. The methodology and anesthesia of castration to minimize associated stress and pain is currently the focus of heavy research. The acute distress of castration is effectively eliminated by the administration of local anesthetics, which is the most commonly used anesthesia protocol for castrating food animals. However, the integrated cortisol response is less efficiently controlled with local anesthesia alone, and a multimodal approach to anesthesia should be considered, particularly when castration is performed in older animals [5]. There are currently no drugs labeled for the control of surgical pain in farm animals in the USA other than local anesthetics. Nonsteroidal anti‐inflammatory drugs (NSAIDs) in conjunction with local anesthetics effectively minimize the acute and prolonged pain response associated with castration. Labeled for the control of inflammation or as an antipyretic, flunixin meglumine (1.1–2.2 mg/kg) is the sole NSAID labeled for use for farm animals in the USA and must be given intravenously at least daily for efficacy. Longer‐acting NSAIDs, such as meloxicam, may be used more effectively to control pain associated with castration when used in accordance with extralabel drug use regulations [5].

Young ruminants: Castration in young ruminants can be done with the animal standing or in lateral recumbency; adequate physical restraint in either case is required. Infusion of 2% lidocaine in the skin and/or spermatic cord can then be performed, although many procedures are done with only physical restraint to minimize the time of the procedure and the stress of being separated from the dam. A small‐gauge needle is used to infiltrate 1–3 ml of 2% lidocaine in the scrotal skin along the proposed line of the incision. An additional 1–2 ml may be injected into each spermatic cord. Vasodilation associated with lidocaine increases the risk of hemorrhage but, in the experience of the author, has not resulted in clinically significant blood loss. Dilution of lidocaine with sterile saline to a final concentration of 0.5–1% should be considered in lambs and kids due to their sensitivity to local anesthetics. General anesthesia or heavy sedation is sometimes used in pet animals; injectable anesthesia is usually sufficient to provide ample time for the procedure. Intravenous (IV) administration of ketamine (2–3 mg/kg) and xylazine (0.1–0.2 mg/kg) will usually provide 20–30 minutes of anesthesia. Other drugs can also be used successfully (Chapter 4), and the choice of agents will depend on the anesthetist’s or surgeon’s preference.

Adult ruminants: Several local blocks have been described for the castration of older, or mature, ruminants. In addition to the aforementioned techniques, anesthesia can be provided by injecting 10–15 ml of 2% lidocaine subcutaneously in a ring block of the scrotal neck, followed by the administration of 5 ml of 2% lidocaine into each spermatic cord. When castration of several patients is to be performed, the animal can be released and the block performed on other patients to allow a 10‐minute period for the onset of anesthesia. Alternatively, intratesticular administration of a local anesthetic can be performed in addition to subcutaneous (SC) infiltration of the scrotal skin. In mature animals, a 3.75–7.5‐cm, 16‐ to 18‐gauge needle is used; for smaller animals, a 2.5–3.75‐cm, 20‐gauge is preferred. With the testicle grasped firmly, the needle is inserted just ventral to the tail of the epididymis and advanced toward the center of the testicle at approximately a 30° angle from perpendicular. Depending on the size of the animal, 2–15 ml of 2% lidocaine is deposited at the center of the testicle. Sedation is more commonly used when performing castration on older ruminants. General anesthesia using either injectable or inhalation anesthetics should be considered for mature animals or when physical restraint is inadequate.

Camelids: Castration of New World camelids is best performed with some degree of sedation or general anesthesia although the procedure can be performed with adequate physical restraint and local anesthesia. Camelids are less sensitive to the effects of xylazine than small ruminants, thus a higher dose of the drug is usually required to achieve a comparable state of sedation. Mild sedation with xylazine (0.3 mg/kg IV) with local infiltration of the skin of the surgical site is adequate. If heavier sedation is desired, xylazine can be administered in conjunction with ketamine. Xylazine (0.6 mg/kg intramuscular [IM]) and ketamine (6 mg/kg IM) provide satisfactory sedation for castration of llamas. In alpacas, the doses are increased slightly to 0.7 mg/kg IM of xylazine and 7 mg/kg IM of ketamine. Llama Lullaby produces short‐term anesthesia in llamas and alpacas for completion of short surgical procedures, including castration, and is favored by the author for field procedures. The solution is made by combining 1 ml (100 mg) of xylazine, 1 ml (10 mg) of butorphanol, and 10 ml (1000 mg) of ketamine. The resulting combination is administered intramuscularly at a dose of 1 ml/23 kg (50.6 lb) for llamas or 1 ml/18 kg (39.6 lb) for alpacas to provide approximately 20–30 minutes of anesthesia. General anesthesia using inhalation anesthetics is a viable option; addition of a local infiltration of 2% lidocaine to the incision site is recommended for additional pain management [6].

Swine: In swine, castration is ideally performed before 2 weeks of age to minimize stress and behavioral changes associated with castration. Piglets are best castrated by suspending them by the hind limbs in vertical restraint. Anesthesia is provided by injecting 0.5–1.0 ml of 2% lidocaine into the scrotal skin over each testicle and 0.5 ml into each spermatic cord in the inguinal canal. Heavy sedation or general anesthesia is preferred for the castration of older pigs. A combination of tiletamine, zolazepam, ketamine, and xylazine (TKX‐P) for pigs is favored by many clinicians. The combination is formed by reconstituting one 500 mg vial of Telazol with 250 mg (2.5 ml) of ketamine and 250 mg of xylazine (2.5 ml). The resulting combination is dosed at 1 ml/35–75 kg (77–165 lb) in commercial pigs or 1 ml/75–140 kg (165–308 lb) in potbellied pigs. Alternatively, IM induction of general anesthesia using ketamine (5 mg/kg), midazolam (0.2 mg/kg), and detomidine (0.1 mg/kg) followed by inhalation anesthesia has been described for urogenital surgeries in pot‐bellied pigs [7]. A combination of xylazine and ketamine (2 and 11 mg/kg IM, respectively) provides deep sedation, but pigs may still respond to surgical stimulation. The same combination of drugs, albeit at lower doses (1–2 and 3–5 mg/kg, respectively), can be administered by intratesticular injection to induce immobilization and anesthesia for castration of mature boars. Half the total dose is injected into each testicle; removal of the testicle removes unabsorbed drug residue and hastens recovery.

9.1.2 Penile Papilloma

Penile papillomata represent the most common penile tumor of the bovid, and anesthesia for surgical removal is adequately provided by local or regional techniques. The bull should be restrained in a standing chute or on a tilt table. Mild sedation can be used as needed for fractious animals. The dorsal penile nerve is desensitized by infusion of 2–4 ml of 2% lidocaine subcutaneously across the dorsum of the penis using a 22‐ or 24‐gauge needle. Alternatively, local infiltration of 2% lidocaine around the base of the tumor, particularly for well‐pedunculated papillomata, provides adequate analgesia. A pudendal nerve block will also successfully desensitize the surgical site but is less commonly employed due to a higher degree of technical difficulty of administration.

9.1.3 Persistent Frenulum

Correction of persistent frenula occurs with the bull in standing restraint or lateral recumbency; general anesthesia is not usually warranted. Mild sedation may be employed, but tranquilization is contraindicated as it is desirable that the bull retract the penis into the sheath postoperatively for protection against trauma and as an aid in hemostasis. Analgesia is most easily and commonly provided by local injection of the frenulum attachments with 1–2 ml of 2% lidocaine using a small‐gauge needle. Local anesthesia can also be supplied by inserting a small‐gauge needle through the lamina interna at the dorsal aspect of the preputial orifice. Injection of 2% lidocaine in a semicircle over the dorsal aspect of the penis will successfully desensitize the dorsal penile nerve. Alternatively, regional anesthesia can be provided by the administration of a pudendal nerve block.

9.1.4 Penile Translocation

Penile translocation surgery is performed with the patient in dorsolateral recumbency to allow access to the ventral midline and one flank. General anesthesia is preferred for the procedure, although heavy sedation and local anesthesia are also acceptable. Specific agents to be used will depend on the surgeon’s preference, but a combination of xylazine (0.1 mg/kg IV) and ketamine (2.0 mg/kg IV) or the use of Bovine Triple Drip (1 ml/kg IV for induction, 2 ml/kg/hour for maintenance) works well when injectable anesthesia is indicated. Local anesthesia is provided by infusing 2% lidocaine subcutaneously in a modified ring block approximately 10 cm around the periphery of the preputial orifice and prepuce to within approximately 5 cm of the scrotal neck. A second SC ring block can be performed at the translocation site in the flank.

9.1.5 Epididymectomy

Epididymectomy can be performed in all farm animal species for the process of sterilization or the preparation of teaser animals, often in conjunction with other procedures. General anesthesia is indicated in mature boars and can also be used in small ruminants and camelids but is not required. The choice of injectable or inhalation anesthesia is dictated by surgical conditions, surgeon’s preference, and additional procedures to be performed, if any. When local anesthetic techniques will be solely used, the choice of standing or lateral restraint is at the discretion of the surgeon. The surgical site is desensitized by local infiltration of 2% lidocaine with a small‐gauge needle in the scrotal skin directly over the epididymis. Deposition of 2% lidocaine directly into the epididymis can be considered for additional analgesia but is not commonly performed.

9.1.6 Vasectomy

Like epididymectomies, vasectomies in ruminants are usually performed under local anesthesia; general anesthesia can be considered in small ruminants but is not often practical, and local anesthetic techniques provide adequate analgesia. After the application of standing or lateral restraint, with or without the use of sedation, 2–4 ml of 2% lidocaine is infused into the posterior scrotal skin just proximal to each testicle using a 20‐ or 22‐gauge needle. Infusion of local anesthetic directly into each spermatic cord with a fine needle at the surgery site provides additional analgesia but is believed by some clinicians to hinder identification of the vas deferens. In swine, general anesthesia is recommended. Injectable anesthetic protocols in conjunction with local infusion of lidocaine provide adequate analgesia for the procedure. General anesthesia is also recommended when performing the procedure in New World camelids.

9.2 Urogenital Surgery in the Female

9.2.1 Cesarean Section

Cattle: Patient positioning and surgical approach for the bovine cesarean section will be influenced by multiple factors, including fetal viability, patient’s temperament, available facilities, and clinician experience and preference. Discussion of the benefits and drawbacks of the various approaches is beyond the scope of this text; the standing flank and ventral midline approaches are used most commonly. Both approaches are performed successfully under regional and local anesthesia. Epidural anesthesia is provided at the discretion of the surgeon. A caudal epidural anesthesia using 2% lidocaine will not provide analgesia to the surgery site but will decrease straining. In recumbent animals, this may also decrease the resultant hind limb movement and assist in restraint. In standing procedures, caution is warranted when administering epidurals as excessive anesthesia can result in recumbency. The dose of local anesthetic is 0.5 ml per 45 kg (99 lb) of body weight.

The use of sedatives or tranquilizers is optional for bovine cesarean section and is dictated by the attitude of the patient and available facilities. When a standing approach is preferred, care must be taken not to induce recumbency. Sedation with acepromazine (0.01 mg/kg IV, 0.1 mg/kg IM) is preferred by the authors when performing standing cesarean sections on nervous or fractious patients. Xylazine is a commonly used sedative in bovine medicine and may aid in restraint of recumbent animals. However, the ecbolic activity of xylazine may hinder uterine manipulation and thus is not favored for cesarean sections. Cattle in dorsal or dorsolateral recumbency experience cardiovascular and respiratory compromise, and this must be accounted for when choosing whether to use sedation and, if so, which drug to employ. While sedation or tranquilization is acceptable, and even beneficial in selected cases, local anesthesia and physical restraint are sufficient for most cesarean sections in the bovine patient.

Local blocks providing anesthesia to the paralumbar fossa include the proximal and distal paravertebral nerve blocks, inverted‐L block, and line block; these are discussed in detail in Chapter 8. Selection of a particular block is influenced by the condition of the patient and surgeon’s preference. For ventral midline celiotomies, local anesthesia is provided by the infusion of a field block of 2% lidocaine along the intended incision line. An 18‐gauge, 3.8‐cm needle is used to infuse multiple, small injections of 10 ml of local anesthetic solution subcutaneously and into the deep layers and peritoneum. High‐volume caudal epidural anesthesia (1 ml of 2% lidocaine per 5 kg [11 lb] of body weight) has also been used to facilitate the procedure from the ventral midline approach [8].

Small ruminants: Anesthetic protocols for cesarean sections in small ruminants are similar to those used in cattle and primarily depend on the surgical approach to be used. Local anesthetic techniques are performed as in cattle. However, it must be remembered that small ruminants are much more sensitive to lidocaine than their larger counterparts with the recommended maximum dose not to exceed 6 mg/kg. Regional anesthesia using a lumbosacral epidural is a viable alternative for cesarean sections in sheep and goats; the recommended dose is 2 ml of 2% lidocaine per 10 kg (22 lb) of body weight. An 18‐ or 20‐gauge, 3.8‐cm needle is sufficient in most animals. Onset of anesthesia occurs within 5–15 minutes and generally lasts 60–120 minutes. General anesthesia is also suitable for the procedure in small ruminants. Maintenance with an inhalation anesthetic, such as isoflurane, is preferred.

Camelids: Cesarean sections are less commonly performed in New World camelids than in ruminant species. When indicated, the left lateral abdominal approach is used most commonly. General anesthesia is preferred and either injectable or inhalation anesthetic protocols are suitable; the final anesthetic choice will depend on the drug availability and clinician preference. Llama Lullaby, described above, can be used for injectable anesthesia. However, initial dosing will generally provide only 20–30 minutes of anesthesia and so it is likely that additional doses may be needed depending on the length of the procedure. A similar duration of anesthesia can be achieved using propofol (4.0 mg/kg), a combination of ketamine (2.0 mg/kg) and propofol (2.0 mg/kg), or a combination of ketamine (4.0 mg/kg) and diazepam (0.1 mg/kg) [9]. Additional use of local anesthetic infusions and/or regional anesthetic blocks for enhanced pain management is encouraged.


Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Nov 10, 2022 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Anesthetic Management of Specific Procedures

Full access? Get Clinical Tree

Get Clinical Tree app for offline access