Local and Regional Anesthesia in Veterinary Medicine

Local Anesthetics

Drugs used to temporarily block nerve conduction by inhibiting voltage-gated sodium channels, preventing membrane depolarization and impulse transmission.

Purpose of Local Anesthetics

Minimize pain during medical and surgical procedures, provide postoperative analgesia, reduce the need for general anesthesia.

Ester-linked local anesthetics

Metabolized by plasma esterases, shorter duration.

Amide-linked local anesthetics

Metabolized by the liver, longer duration.

Surface Anesthesia

Directly applied to mucous membranes.

Infiltration Anesthesia

Injected into tissues surrounding the target area.

Regional Anesthesia

Targets major nerves or nerve plexuses.

Intraarticular Anesthesia

Injected into joints for pain relief in arthritic or post-surgical cases.

Subsynovial Anesthesia

Injection into synovial spaces.

Intravenous Regional Anesthesia (Bier Block)

Injected into a vein distal to a tourniquet, used in limb surgeries.

Refrigeration (Hypothermic) Anesthesia

Uses cold temperatures to slow nerve conduction.

Infraorbital Nerve Block

Anesthetizes the upper lip, nose, and roof of the nasal cavity.

Maxillary Nerve Block

Blocks pain in the maxilla, upper teeth, nose, and upper lip.

Mental Nerve Block

Used for the lower lip and chin.

Brachial Plexus Block

Blocks pain in the forelimb up to the elbow, affecting radial, median, ulnar, musculocutaneous, and axillary nerves.

Sciatic and Femoral Nerve Block

Used for hind limb anesthesia, often for orthopedic surgeries.

Lumbosacral Epidural Anesthesia

Used for abdominal, tail, and perineal surgeries.

Indications for Epidural Anesthesia

Provides intraoperative and postoperative analgesia, used in critical care and high-risk patients.

Drugs Used in Epidural Anesthesia

Morphine, Bupivacaine, Dexmedetomidine, Ketamine, Xylazine.

Complications of Epidural Anesthesia

Injection into vertebral sinuses (causing vomiting, tremors, paralysis), respiratory depression and paralysis.

Nociceptive Pain

Arises from injury to tissues, transmitted by intact nervous pathways.

Neuropathic Pain

Caused by nerve damage or dysfunction.

Inflammatory Pain

Results from release of inflammatory mediators.

Pathologic/Maladaptive Pain

Persists beyond normal tissue healing.

Transduction

Activation of nociceptors by a painful stimulus.

Transmission

Pain signal sent to spinal cord and brain.

Modulation

Pain signals can be amplified or suppressed in the spinal cord.

Perception

The brain interprets the pain signal.

Signs of Pain in Animals

Behavioral Changes (Restlessness, aggression, hiding), Postural Changes (Hunched back, stiff movement), Physiological Changes (Increased heart rate, blood pressure, respiratory rate).

Opioids

Morphine, Fentanyl, Hydromorphone, Tramadol.

NSAIDs

Carprofen, Meloxicam, Deracoxib.

Local Anesthetics

Lidocaine, Bupivacaine.

NMDA Receptor Antagonists

Ketamine, Amantadine.

Alpha-2 Agonists

Dexmedetomidine, Xylazine.

Otitis Externa

Inflammation of the outer ear canal.

Otitis Media

Involves the middle ear, may lead to hearing loss.

Otitis Interna

Affects the inner ear, can cause vertigo and head tilting.

Lateral Canal Resection

Improves ventilation of the ear.

Vertical Canal Ablation

Removes the vertical ear canal if diseased.

Total Ear Canal Ablation (TECA)

Removes the entire ear canal; often requires bulla osteotomy.

Complications of Ear Surgery

Hemorrhage, facial nerve damage, infection, hearing loss.

Entropion

Eyelids roll inward, causing corneal irritation.

Ectropion

Eyelids roll outward, leading to dry eye exposure.

Third Eyelid Gland Prolapse (Cherry Eye)

Prolapse of the nictitating membrane gland.

Corneal Ulcers

Common in cats due to fights; requires conjunctival grafting.

Traumatic Proptosis

Eye displacement from the socket, common in brachycephalic breeds.

Tarsorrhaphy

Suturing the eyelids together to protect the cornea.

Enucleation

Removal of the eyeball due to severe trauma or disease.

Postoperative Care

Use of NSAIDs, opioids, and Elizabethan collars to prevent self-trauma.