Sodium Channel Blockers and Local-Regional Anesthesia

Flashcards covering the fundamentals of sodium channel blockers, specific local anesthetics, toxicity protocols, dental and regional nerve blocks, and epidural techniques in veterinary medicine.

Sodium channel blockers

Agents that deactivate sodium channels on the nerve membrane, preventing depolarization of the cell membrane and inhibiting the generation and propagation of nerve impulses.

Lidocaine (Pharmacology)

A local anesthetic with an onset time of $1-5\,\text{minutes}$ and a duration of $30-90\,\text{minutes}$. The dog dose is $4-6\,\text{mg/kg}$ and the cat dose is $2-4\,\text{mg/kg}$. Symptoms of neurotoxicity include sedation, trembling, seizures, and coma.

Bupivacaine (Pharmacology)

A local anesthetic with an onset time of $3-20\,\text{minutes}$ and a duration of $2-6\,\text{hours}$. The dog dose is $1-2\,\text{mg/kg}$ and the cat dose is $1\,\text{mg/kg}$. It is associated with cardiotoxicity, including arrhythmias and cardiovascular collapse.

Nocita

A liposome-encapsulated bupivacaine providing extended release for up to $72\,\text{hours}$. It is FDA approved for dogs and cats at a dose of $0.4\,\text{ml/kg}$ and is NOT recommended for motor nerve blockade.

pKa (Local Anesthetics)

A value that accounts for the speed of onset; lidocaine ($7.9$) has a faster onset than bupivacaine ($8.1$) in normal tissue ($\text{pH } 7.4$). These basic drugs are less effective in inflamed (acidic) environments where they become highly ionized.

Dexmedetomidine (Adjunct)

An alpha-2 agonist that peripherally vasoconstricts to decrease absorption and increase the duration of a blockade.

Buprenorphine (Adjunct)

A partial mu agonist opioid with sodium channel blockade properties that can extend the duration of a block from $6\,\text{hours}$ to $18\,\text{hours}$.

Lipid emulsion infusion

A rescue treatment for local anesthetic toxicity administered as a $4\,\text{ml/kg}$ IV bolus over $2\,\text{minutes}$, followed by a CRI at $0.5\,\text{ml/kg/hr}$ for $2-5\,\text{hours}$.

Trigeminal nerve (CN V)

The nerve supply to the head consisting of three branches: the ophthalmic nerve (sensory to eyes/forehead), maxillary nerve (sensory to upper jaw/teeth), and mandibular nerve (sensory to lower jaw/teeth and motor to muscles of mastication).

Infraorbital nerve block

A technique that blocks transduction of noxious stimuli to the rostral aspect of the maxilla, including the carnassial tooth (upper 4th premolar).

Maxillary nerve block

A block providing anesthesia to the entire upper jaw and face, indicated for caudal dental extractions, maxillectomies, and nasal procedures.

Inferior alveolar (mandibular) nerve block

A block that desensitizes the lower lip, teeth, gingiva, and part of the tongue; it is performed by palpating the nerve behind the last molar, medial to the mandible.

Mental nerve block

A block that desensitizes the area rostral to the mental foramen, primarily used for rostral dental extractions and biopsies.

Retrobulbar block

A procedure indicated for enucleation and intraocular surgery using a $1.5\,\text{inch } 22\,\text{g}$ needle curved at a $20-40\,\text{degree}$ angle, walked around the bony orbit caudal to the globe.

RUMM block

Stands for Radial, Ulnar, Median, and Musculocutaneous nerve block; it desensitizes the front limb distal to the elbow, though it does not fully block the elbow itself.

Intercostal nerve block

A technique used for thoracotomy incisions or chest tubes that blocks the thoracic wall (not viscera) by injecting local anesthetic at the caudal border of the rib in the proximal $1/3$ quadrant.

Testicular block

A block performed by injecting anesthetic into the body of the testicle while aiming toward the spermatic cord, often using $1\,\text{mg/kg}$ bupivacaine or $4\,\text{mg/kg}$ lidocaine divided between both testicles.

Ligamentum flavum

The ligament that provides a characteristic 'pop' or 'loss of resistance' when penetrated by a spinal needle during an epidural injection.

Opioids in Epidurals (Morphine)

Substances that bind to opioid receptors in the dorsal horn neurons to prevent pain signal modulation. Morphine doses are $0.05-0.15\,\text{mg/kg}$ with a duration of $12-20\,\text{hours}$, and side effects include pruritus and urinary retention.

Caudal (sacrococcygeal) epidural

A block performed at the $S-C1$ or $C1-C2$ joint that provides anesthesia to the tail, perineal region, penis, vagina, urethra, colon, and anus.

Lidocaine Infusion (CRI)

A multi-modal analgesia technique used for visceral pain (e.g., pancreatitis), maintaining steady plasma levels at a rate of $1.5-4\,\text{mg/kg/hr}$ in dogs and $0.5-2\,\text{mg/kg/hr}$ in cats.