Porcine Surgical Procedures

Porcine Surgical Procedures

Swine Surgery and Anesthesia

Although the vast array of surgical procedures and technology available for other species are available for swine, economic considerations usually make many procedures impractical except for valuable breeding stock and valued pets.

Standing surgery is an option only for a few minor procedures. Most surgeries on swine are performed with the animal in recumbency, using either general anesthesia or a combination of local anesthesia and sedation. As in other species, whenever possible, local anesthesia and sedation are preferred to general anesthesia. Swine face the same risks associated with general anesthesia as other species but with the additional concerns of high body temperatures and possible development of malignant hyperthermia under general anesthesia. Malignant hyperthermia, which is part of the porcine stress syndrome, occurs rarely in swine during inhalation anesthesia.

Potbellied pigs can be anesthetized using the techniques used for the other swine breeds. Small animal anesthesia machines and equipment can be used for pigs of this size. Malignant hyperthermia is extremely rare in potbellied pigs.

Local Anesthesia

Lumbosacral Epidural Anesthesia

Epidural anesthesia in swine is performed at the lumbosacral junction. No other epidural site is readily accessible in this species. The epidural space at this location is fairly large and easy to enter with a needle. Anesthesia administered at this location is considered to be a “cranial epidural” as opposed to the “caudal epidural” frequently used in other large animal species. Epidurals are frequently performed as analgesia for cesarean section surgery, and the systemic effects on the fetuses are minimal.

The proper site for the epidural must be identified. The lumbosacral junction is just caudal to a line drawn transversely through the animal to connect the crests of the wings of the ilium, where the line bisects the dorsal midline. In small swine, the wings of the ilium are palpable. In large swine, anatomical landmarks must be relied upon to locate the site. Large swine are preferably injected in the standing position, standing squarely on all four legs. Looking at the pig from the side, a vertical line is drawn upward from the patella; this line usually identifies the cranial extent of the crest of the ilium. The needle is inserted 1 to image inches caudal to this line, on dorsal midline (Fig. 24-1).

The animal should be sedated for the procedure, if possible, and/or restrained with a hog snare. The hair is clipped, and the skin aseptically prepared. Up to 5 ml of 2% lidocaine is deposited subcutaneously to a depth of 1 to 2 inches to reduce discomfort and patient movement during the actual epidural block. A final scrub is applied to the skin.

Sterile gloves should be worn for the procedure. The needle for the epidural should be an 18- to 20-gauge (ga) spinal needle. A 3-inch-long needle is necessary for small swine, a 4-inch needle for swine weighing more than 100 kg, and a 5- to 7-inch needle for swine weighing 200 kg or more. These needles are easily bent, and some clinicians prefer to use a shorter (1- to 2-inch) 14-ga needle as a protective sleeve trocar for the 18-ga needle. The 14-ga needle is placed first, and then the 18-ga needle is passed through its lumen.

Lidocaine 2% (without epinephrine) is an anesthetic drug commonly used for the block. The dose used depends on the body weight of the patient and the desired effects, ranging from 0.5 to 1 ml per 4.5 kg of body weight (maximum 20 ml). Lower doses provide analgesia caudal to the lumbosacral area, but higher doses can diffuse and produce analgesia as far cranially as the first lumbar vertebra. Anesthesia begins approximately 5 to 10 minutes after injection, reaches a maximum at 20 minutes, and lasts as long as 2 hours.

Xylazine can also be injected into the lumbosacral epidural space. At a dose of 2 mg/kg (diluted in 5 ml of sterile saline), it produces surgical anesthesia of the body caudal to the umbilicus and paralysis of the hindlegs. The analgesic effects begin within 20 to 30 minutes and may last up to 2 to 3 hours. The dose is important because doses up to 1 mg/kg do not produce surgical anesthesia, and doses 3 mg/kg or greater cause prolonged hindlimb paresis and ataxia that last for 36 hours or more. Lidocaine 2% can be mixed with xylazine to give a more rapid onset of analgesia (5 minutes), which may last as long as 5 hours.

Remember that epidural anesthesia does not desensitize or immobilize the head, neck, or forelimbs of an animal. The animal must be controlled with physical restraint, sedation, or both.

General Anesthesia

Anesthetic Risks for Swine

Before administering anesthesia to swine, the following risks should be considered.

Swine Are Prone to Hypoventilation

Inadequate ventilation may result in hypoxemia, which may lead to death. Several potential sources of ventilation problems may exist alone or in combination.

Airway obstruction

Any factor that decreases the cross-sectional area of the upper airways greatly increases the resistance to breathing.

• The larynx of swine is sensitive to physical stimulation. Pressure and touch, even from accumulated saliva, can trigger a laryngospasm.

• The laryngeal lumen of the pig is small in relation to the size of the animal. A pig weighing 100 kg requires an endotracheal tube that would fit a large dog (≈14-mm internal diameter). Flexing the neck partially occludes the laryngeal entrance. Salivation, which is common in anesthetized pigs, can result in accumulations of saliva in the pharynx and laryngeal entrance that actually occlude the larynx.

• Laryngeal edema results readily in swine due to their relatively fragile laryngeal mucosa. The laryngeal mucosa is quite easy to traumatize during endotracheal intubation and responds quickly with swelling. This edema of the larynx causes further narrowing of the already small lumen diameter.

Swine Are Prone to Hyperthermia under Anesthesia

Although swine have sweat glands in the skin, the glands do not function efficiently in thermoregulation of the animal. Subcutaneous accumulation of fat contributes to the development of hyperthermia. Also, swine have a low amount of body surface area for their body size, which inhibits the dissipation of heat. Because of these factors, body temperature tends to rise when swine are anesthetized, and the effects may be increased if anesthesia is performed in a hot environment.

Occasionally, malignant hyperthermia develops in genetically predisposed animals. This condition develops rapidly and is difficult to control, and the outcome typically is fatal.

Preanesthetic Preparation and Anesthetic Management

Preanesthetic Drugs

Because so few superficial veins other than the ear veins can be accessed, most preanesthetic and injectable anesthetic drugs are given intramuscularly (IM). The location of intramuscular injection can affect the speed and depth of anesthesia. Intramuscular injection into the gluteal, back, or shoulder muscles provides more consistent results than injections into the neck muscles; however, gluteal injections risk damaging a valuable cut of pork (ham). The neck muscles have numerous fascial (dense connective tissue) planes; accidental injection into fascia may cause uneven, slow absorption with unreliable results. If the neck muscle is used, the safest site for injection is just caudal to the base of the ear, where there is less fascia in the muscle.

Atropine is sometimes used to control salivation in swine, which can be excessive. Atropine is given at a dosage of 0.044 mg/kg IM.

Induction Drugs

Various anesthetic induction and maintenance regimens are available for swine. Withdrawal times for meat-producing animals should be observed. A quiet induction area is preferred. Restraint in a chute or crate is generally less stressful than other forms of physical restraint (e.g., snout restraint). Some of the techniques in use are listed in Box 24-1.

BOX 24-1   Anesthetic Induction and Maintenance Regimens Available for Swine

• Telazol/ketamine/xylazine (TKX): All three drugs are mixed together in the Telazol vial and given intramuscularly (IM). This popular combination provides short-term anesthesia (20–30 minutes). It also can be used for stages from induction to inhalant gas maintenance. Endotracheal intubation can be performed with this combination. Repeated injections of the combination can be used to extend the length of general anesthesia. Recovery from anesthesia occurs in 60 to 90 minutes.

• Atropine/acepromazine/ketamine: Atropine and acepromazine are given IM, followed by ketamine IM approximately 20 minutes later. This combination is useful for minor, short procedures. Anesthesia lasts approximately 10 to 15 minutes. Analgesia must be supplemented with local anesthetics for painful procedures.

• Atropine/xylazine/ketamine: Atropine and xylazine are given IM, followed by ketamine IM approximately 10 minutes later. Anesthesia lasts about 10 to 15 minutes.

• Xylazine/Telazol: Xylazine is given IM, followed by Telazol IM 5 minutes later. Although analgesia and muscle relaxation are good, the depth of surgical anesthesia may be light and of short duration. Drowsiness after recovery may be prolonged (up to 24 hours).

• Intratesticular sodium pentobarbital: A technique for anesthesia for castration of large boars has been described. Sodium pentobarbital is injected into each testicle to produce anesthesia in approximately 5 minutes. Removal of the testicles effectively removes the source of the anesthesia.

• Inhalant gases: Mask induction, with or without prior sedation, can be used in small or heavily sedated swine. Halothane, isoflurane, and sevoflurane all are suitable for use in swine, but halothane is generally avoided because of the risk of inducing malignant hyperthermia in susceptible families of swine.

• Intravenous thiobarbiturates: An intravenous catheter or butterfly administration set can be used in the ear vein to inject thiobarbiturates. This may be the safest choice for anesthesia in pigs from family lines susceptible to malignant hyperthermia.

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Aug 11, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Porcine Surgical Procedures

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