Local Anesthetics

What are the uses of local anesthesia and regional anesthesia in veterinary medicine?

• Most often used in conjunction with sedation or general anesthesia

• Reduce amount of general anesthetic

• Minimizing cardiopulmonary depression

• Provide a useful analgesia

• Techniques are not difficult to learn and do not need expensive equipment

Common Local Anesthetics

• Lidocaine

• Bupivacaine

• Mepivacaine (equine)

• Prilocaine

Lidocaine

• Most widely used general purpose local anesthetic in veterinary use

• Reasonably rapid onset of action, with good spreading property

• May cause some local irritation and swelling - horse

• Duration of action is variable (around 1 hr)

• Dose: 1-2 mg/kg

• Treat VPC (Ventricular Premature Complex): give intravenously (IV)

Bupivacaine

• Relatively slow onset (15-30 minutes)

• A prolonged duration of action; up to eight hours when combined with epinephrine

• Most cardiotoxic durg (when it is given via IV)

• It is used whenever long action is required (post op analgesia; prolonged surgery etc).

• Commonly used in vet med

• Dose: 0.5-2 mg/kg

Before you administer local anesthetic to the patient…..

ALWAYS aspirate first and administer local anesthetics

Liposome-Encapsulated Bupivacaine

• Nocita

• Used as a local postoperative analgesic

  • Orthopedic surgery

  • Onychectomy in cats

  • Limb amputation

• Can last 72 hours or more after surgery

• Currently available in 10 ml or 20 ml vial

Transdermal local anesthetics

• Lidocaine patches

• Treat superficial pain

• Used for

  • post-op laparotomy

  • post-op mastectomy

• Inexpensive

• Cuttable, non-controlled

• Onset up to 12 hours

What are some examples of local anesthetics/ blocks in dogs and cats?

• Topical (surface) anesthesia

• Carpal block - ring block

• Intravenous regional block (bier block)

• Brachial plexus block

• Intercostal nerve block

• Spinal & epidural anesthesia

• Dental block

• Intratesticular block

Topical (surface anesthesia)

• Use of local anesthetics in solution sprays, creams and ointment

• On mucous membranes, in the eyes, in laryngeal area

Intravenous regional block (bier block)

• Safe, short term anesthesia of extremity

• Place an IV catheter distally (cephalic or saphenous)

• Wrap tourniquet proximally

• Lidocaine 2 mg/kg, IV

• Analgesia will last up to 30 minutes

Brachial plexus block

• provide analgesia distal to the shoulder joint in forelimb

Anatomy of brachial plexus block

Blocks C6, C7, C8, and T1

Nerve locator

• Used to locate each specific nerve to block

• Small amount of local anesthetic required

• Complete block can be achieved

• Training and practice required

Intercostal nerve block

• Need to block minimum of three consecutive ribs

• Intercostal nerves and vessels lie adjacent to the caudal border of each rib

• Inject small amount (less than 0.5 ml per site) of local anesthetic

• Bupivacaine: up to 2 mg/kg

Epidural anesthesia

• Injection of local anesthetic in the epidural space to block motor, sensory and autonomic system

• Decrease inhalant requirement

• Decrease postoperative analgesic requirement

For epidural anesthesia, the area blocked will depend on…

• The site on injection

• Quantity, volume of local anesthetic injected

• Size of spinal canal (obese and pregnant patients reduce 50% of calculated dose)

• Position of animal

What are the two sites of injections for epidural anesthesia?

• Lumbosacral (L7-S1)

• sacrocoxygeal or intercoxygeal

Indications for epidural anesthesia

1. Hindlimb surgery

2. Tail, perineal region surgery

3. Abdominal surgery

Epidural anesthesia contraindications

• Septicemia

• Skin infection over the injection site

• Coagulation problems

• Neurological patients

• Direct trauma to the injection site

Epidural anesthesia complications

• Neurotoxicity with preservative - use preservative free drugs

• Pelvic limb paresis and hyperalgesia

• Ventilatory impairment if excessive cranial migration of the drug

• Urinary retention with opioid - require postoperative monitoring

What are the commonly used epidural anesthetic drugs?

• Morphine (0.1 mg/kg)

• Bupivacaine (0.5 mg/kg)

• dexmedetomidine (0.005 mg/kg)

• Ketamine (0.1 mg/kg)

Three common dental blocks?

• Infra-orbital foramen

• Mental foramen

• Mandibular foramen

“lack of resistance” technique

indicates proper placement of the injection needle in the epidural space based on the amount of resistance to the injection of air or saline

“hanging drop” technique

• involves removing the stylet of the spinal needle, filling the hub of the needle with saline or anesthetic solution, and allowing one drop to hang from the hub

• when entering the epidural space, the negative pressure in the epidural space will draw the drop of solution into the needle

Epidural technique

• Sternal recumbency with head elevated

• Identify the wings of the ilium and take an imaginary line between them crossing the dorsal spinous process of the last lumbar segment