Local Anesthesia in Horses

Local Anesthesia in Horses


Many diagnostic and surgical procedures can be performed safely and humanely on horses by coupling physical restraint and sedation with surface (topical) anesthesia, infiltration anesthesia, nerve block (regional) anesthesia, or epidural anesthesia. Peripheral nerve blocks, intraarticular and intrabursal injections, and local infiltrations (ring block) are used to diagnose equine lameness and to anesthetize surgical sites. Desensitization of the auriculopalpebral nerve is most frequently used to prevent voluntary closure of the eyelids during examination and treatment of the eye. Although regional anesthesia of the head can be induced by various techniques, the most frequently desensitized nerves are the supraorbital, infraorbital, and mandibular alveolar nerves.

Caudal epidural anesthesia is used to facilitate surgery involving the tail, perineum, anus, rectum, vulva, vagina, and urethra and for symptomatic relief of painful conditions during obstetric manipulations.

Improper injection techniques contribute to inadequate anesthesia. Overdosing potentially leads to more serious complications including ataxia of hindlimbs, hindlimb motor blockade, recumbency, and respiratory depression.

Regional Anesthesia of the Head

Anesthesia of the upper eyelid and forehead

Area blocked: upper eyelid except medial and lateral canthi

Nerve blocked: supraorbital (or frontal) nerve

Site: supraorbital foramen (Fig. 6-1, A)

Needle: 22- to 25-gauge, 2.54-cm

Anesthetic: 5 mL of 2% lidocaine

Method: palpate the supraorbital foramen approximately 5 to 7 cm above the medial canthus where it perforates the supraorbital process of the frontal bone; insert the needle into the foramen to a depth of 1.5 to 2 cm; inject 2 mL of lidocaine into the foramen; 1 mL as the needle is withdrawn and 2 mL subcutaneously over the foramen


II Akinesia of the eyelids

III Anesthesia of the upper lip and nose

IV Anesthesia of the lower lip and premolars

Caudal epidural anesthesia

Area blocked: tail, perineum, anus, rectum, vulva, vagina, urethra, and bladder

Nerves blocked: coccygeal and last three pairs of sacral nerves

Site: epidural space in the first intercoccygeal space (Co1 to Co2) (Fig. 6-2)

Needles: spinal with stylet (spinal: 18-gauge, 5.1- to 7.6-cm)

Anesthetic: 6 to 10 mL of 2% lidocaine; other drugs can be considered (see Table 4-2)


1. Use proper restraint, depending on the horse’s temperament; clip, surgically scrub, and disinfect the injection site; make a skin wheal and infiltrate the tissues down to the interarcuate ligament with 1 to 3 mL of 2% lidocaine to minimize movement while inserting the spinal needle

2. Method A (see Fig. 6-2, A): insert the spinal needle into the epidural space in the center of the first intercoccygeal space (about 5 cm cranial to the origin of the first tail hairs and the caudal fold of the tail) at a right angle to the general contour of the croup and press the needle ventrally in a median plane until it strikes the floor of the vertebral canal; withdraw the needle about 0.5 cm

3. Method B (see Fig. 6-2, B): insert the spinal needle about 2.5 cm caudal to the first intercoccygeal space and slide its point ventrocranially at an angle of about 30 degrees to the horizontal plane and to its full length into the vertebral canal

4. Test with a syringe of air for resistance to the injection; alternatively, fill the needle hub with isotonic saline solution and manipulate slightly until the solution is aspirated from the needle by subatmospheric epidural pressure (hanging drop technique); inject local anesthetic; needle can be left in place with stylet reinserted; maximum blockade may require 10 to 30 minutes, and it is not advisable to redose during this time if surgery is to be done with the horse standing


Common causes for inadequate anesthesia or incomplete block

1. Improper injection technique

2. Inappropriate angulation of the spinal needle

3. Horses that have fibrous connective tissue from previous epidural injections, which limits diffusion of anesthetic agent

4. Anatomic peculiarities

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Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Local Anesthesia in Horses

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