Anesthetic Procedures and Techniques in Pigs

Anesthetic Procedures and Techniques in Pigs

“I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it.”

GEORGE BERNARD SHAW

Overview

Anesthesia of pigs is a unique challenge. No approved anesthetic drugs are marketed for use in swine in the United States. Swine have few superficial veins that are easily accessible, other than those on the dorsal surface of the ear; ear veins may be difficult to use because of prior identification and tagging procedures. Most chemical restraining drugs are administered intramuscularly (IM). Pigs are difficult to orotracheally intubate because of their small oral cavities, large tongues, long soft palates, and the presence of a pharyngeal diverticulum. Respiratory depression and elevated body temperature may occur after sedation and general anesthesia. Respiratory depression can be caused by the combined respiratory depressant effects of anesthetic drugs and the limited expansion of the chest wall because of abnormal body positioning and body fat. Elevations in body temperature occur because of the relatively low body surface area to body mass ratio, the relative absence of effective sweat glands, and inefficient thermoregulatory mechanisms. Hyperpyrexia and malignant hyperthermia can occur in genetically predisposed pigs and is triggered by intravenous (IV) drugs such as ketamine and inhalant anesthetics such as isoflurane. Physical restraint combined with sedatives, tranquilizers, and local anesthetic techniques, is commonly used to complete simple surgical procedures in pigs. General anesthesia with inhalant anesthetics provides excellent, stable anesthesia for prolonged surgical procedures.

General Considerations

I Surgical preparation of the pig

A Obtain a history and complete a physical examination; pay particular attention to the respiratory system

B Withhold food for 6 to 10 hours in adult pigs

C Do not withhold water

D Avoid stressing the pig; leave it with other pigs until it is sedate

II Preanesthetic evaluation (see Chapter 2)

A Physical examination including determination of body weight

B Basic laboratory tests (hemogram, white blood cell count), if indicated

III Injection sites

A IM injections should be made in the cervical region (neck)

B IV injections are administered in auricular veins

IV Withdrawal times for medications

A All anesthetic drugs used in swine are “extra-label”

B Suggested withdrawal times are available from The Food Animal Residue Avoidance & Depletion Program’s Food Animal Residue Avoidance Databank (FARAD) at www.farad.org

Preanesthetic Medications

I Azaperone (availability is limited)

A Butyrophenone tranquilizer

B The most effective tranquilizer in pigs

C Dose: 2 to 6 mg/kg of body weight IM, use lower doses in older pigs

D Rapid onset: 5 to 10 minutes after IM

E Duration: 30 minutes after IM

F Large doses may induce deep sedation and hypotension

A Produces minimal sedation and muscle relaxation in pigs

B Dose: 0.2 to 5 mg/kg IM; 0.2 to 0.5 mg/kg IV

III Midazolam (similar to diazepam)

A Dose: 0.1 to 0.5 mg/kg IV or IM; reportedly twice as potent as diazepam

A Produces short-term effects in pigs. Pigs may lie down but are arousable.

B Dose: 1 to 2 mg/kg IM

C Effective in combination with ketamine with or without an opioid

V Dexmedetomidine

A Produces bradycardia, hypertension, and respiratory depression

B Dose: 0.005 to 0.010 mg/kg IV or IM

C Effective in combination with ketamine with or without an opioid

VI Acepromazine

A Does not produce potent sedation; more effective when used in combination with xylazine

B Dose: 0.1 to 0.2 mg/kg IV or IM

Anesthetic Procedures

I Telazol-ketamine-xylazine

A Formulation: reconstitute 500 mg of Telazol powder with 2.5 mL of xylazine (100 mg/mL) and 2.5 mL of ketamine (100 mg/mL)

B Administer the combination IM at 1 to 2 mL/25 kg body weight; limit initial dose to 3 mL

C Provides useful restraint and short-term anesthesia

D Orotracheal intubation can be performed (mask with inhalant if required)

E Compatible with inhalant anesthetics

F Duration of action is 20 to 30 minutes; recovery occurs in 60 to 90 minutes

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Tags: Handbook of Veterinary Anesthesia

Sep 6, 2016 | Posted by admin in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off

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