2.1 Principles and Indications of Local Anaesthesia

What are local anesthetics?

Drugs that reversibly block the generation and propagation of electrical impulses in nerves.

How are local anesthetics administered in horses?

Perineural injection, intraarticular injection, epidural injection, tissue infiltration, topical administration.

What are the uses of local anesthetics in horses?

Regional anesthesia/analgesia, surgical anesthesia, adjunct to general anesthesia, lameness localisation.

What are contraindications for local anaesthesia?

Fracture confirmation, septic inflammation (periarticular cellulitis, hoof abscesses)

What are the two main regions for regional anesthesia in horses?

Head and limbs.

What are the risks associated with regional anesthesia?

Ataxia of hind limbs, hind limb motor blockade, recumbence, respiratory depression.

What types of regional anesthesia are used for the limbs?

Peripheral nerve blocks, intraarticular/intrabursal injections, local infiltrations (ring blocks).

What drugs are commonly used for regional anesthesia of the limbs?

Lidocaine, mepivacaine.

What is the procedure for regional anesthesia of the limbs?

Restrain patient, prepare injection site, deposit LA next to nerve, check for desensitization.

What are the common nerve blocks for the forelimb?

Palmar digital nerve (foot cartilages), midpastern semi-ring block, PDN (proximal sesamoid bones), low palmar nerve block, high palmar nerve block, lateral palmar nerve block, median nerve, ulnar nerve, medial cutaneous antebrachial nerve.

What are the common nerve blocks for the hind limb?

Plantar digital nerve, midpastern semi-ring block, PDN, low plantar nerve block, high plantar nerve block, tibial and peroneal nerve blocks, deep and superficial peroneal nerves.

What are the nerve blocks of the head?

1. Auriculopalpebral nerve block

2. Diamond block (Supraorbital, lacrimal, zygomatic, infratrochlear)

3. Retrobulbar nerve block

4. Maxillary nerve block

5. Infraorbital nerve block

6. Mandibular nerve block (inferior alveolar nerve block)

7. Mental nerve block

How is anesthesia for castration achieved?

Local infiltration of the testicles with mepivacaine.

What is the typical dosage of mepivacaine for castration off full-sized adult horses?

10ml per testicle.

What is epidural anesthesia?

Injection of an anesthetic into the subarachnoid space. Used on a standing horse.

What are the indications for epidural anesthesia in horses?

1. Anaesthesia of the perineum

2. rectovestibular laceration repair

3. miscellaneous surgeries involving rectum, anus, perineum, tail, urethra, bladder, vulva, vestibule, or vagina.

4. Relaxation of abdominal contractions during dystocia.

5. Analgesia of the perineal area and hind limbs of adult horses.

6. Analgesia or anaesthesia of the perineal area, hind limbs, and abdomen of neonates.

What drugs are commonly used for epidural anesthesia?

Local anesthetics (lidocaine, mepivacaine, ropivacaine)
alpha2 agonists (xylazine, detomidine)
opioids (morphine, methadone, hydromorphone)
tramadol
ketamine.

What factors should be considered when choosing a drug for epidural anesthesia?

Desired level of anesthesia, duration of action, potential side effects.

What is the procedure for epidural anesthesia?

Clean the injection site, insert the needle into the epidural space, inject the anesthetic.

Where are the injection sites for epidural anaesthesia?

• Between 1st and 2nd coccygeal vertebrae, OR

• Lumbosacral space

• DO NOT USE PROXIMAL EPIDURAL SPACE!!! (withers)

What are the potential side effects of epidural anesthesia?

Ataxia of hind limbs, hind limb motor blockade, recumbence, respiratory depression.

Which drugs for mydriasis of the eye?

Atropine, adrenaline

Which nerves are injected for dental procedures, especially maxillary cheek teeth?

• Maxilla: Maxillary, infraorbital

• Mandibula: Mandibular, mental

Which nerve block is near the eye?

Auriculopalpebral

Where in the limb are local anaesthetics injected for distal limb nerve blocks?

Perineural

What is the sexual repercussion of using drugs like acepromazine?

Priapism (penis prolapse).