Anesthetic Procedures and Techniques in Horses

Anesthetic Procedures and Techniques in Horses


Horses may be the most difficult domestic species to safely anesthetize. Mortality rates for horses are significantly higher than for cats and dogs, ranging from 1% to 2% in horses compared with about 0.1% in dogs and cats. Individual equine temperament varies considerably and has significant influence on the dose of drug required and selection of the anesthetic technique. The ability to anticipate drug effects and drug actions in horses is the single most important aspect of safe and effective equine anesthesia. Appropriate preanesthetic medications in conjunction with boluses and infusions (total intravenous [IV] anesthesia) of anesthetic drugs are combined with physical restraint to induce general anesthesia in horses. Anesthetic techniques are designed to produce rapid and safe induction to and recovery from recumbency and to maximize muscle relaxation and analgesia while maintaining optimal cardiopulmonary status. Horses frequently benefit from assistance in regaining and maintaining a standing position after general anesthesia.

General Considerations

Preparing the horse for surgery

Withhold food for approximately 4 to 8 hours before surgery except in foals

Perform a complete physical examination with emphasis on cardiorespiratory function

Determine body weight using a scale or a girth weight estimator tape

Groom the horse and wipe with a moist cloth to remove dander and debris

Clean the feet before induction; pull or pad shoes to prevent injury

Prepare (clip and scrub) the surgical site before induction (if possible) to reduce anesthesia time

Place and secure an IV catheter in a jugular vein before induction (Fig. 22-1 A, and B)

Administer preanesthetic medications (antibiotics, analgesic drugs) 5 to 30 minutes before induction

Rinse the mouth thoroughly with water before induction

II Proper positioning and appropriate padding of the head, shoulder, and hip minimize the incidence of neuropathies and myopathies

III All spontaneously breathing horses develop an acid-base disturbance under anesthesia, particularly respiratory acidosis (increased PaCO2) or hypoxemia (PaO2 < 60 mm Hg) when breathing air

IV Controlled positive pressure ventilation can be used to maintain normal PaCO2 and may help to maintain arterial blood oxygenation (PaO2)

Prevent hypotension and hypoxemia to help avoid perioperative complications, including myopathy

VI Horses should be closely monitored during the recovery period and, if needed, assisted to a standing position

Preanesthetic Evaluation

Review history

II Conduct a physical examination

III Conduct a laboratory evaluation

Preanesthetic Medications (Fig. 22-2, A)

Xylazine (used to produce sedation, analgesia, and muscle relaxation)

II Detomidine (similar to xylazine)

III Dexmedetomidine (similar to xylazine)

IV Romifidine (similar to xylazine)

Acepromazine (used to produce a calming effect)

VI Chloral hydrate (infrequently used to produce or enhance sedation); 20 to 80 mg/kg IV (see Chapter 8)

Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Anesthetic Procedures and Techniques in Horses

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