Local Anesthetics Flashcards
Types of regional anesthesia
Nerve pathway
- neuroaxial = epidural or spinal
- perinerual = brachial plexus block
Types of general anesthesia
Systemic /full body effect
Volatile (inhalants or injectables)
Types of local anesthetics
Topical - skin, mucosa (surface)
Infiltrative - line block, testicular (below surface)
Indications for LA and SA
LA - common w heavy sedation
SA - normally combined w general anesthesia
Monitor patients & provide oxygen
Goals for using local anesthesia
Reduces anesthesia requirements when combined w GA, reducing the GA side effects
^ cardio function
Better pain control
Sodium channel blockers
Not specific for pain pathways
Block transduction & transmission at site, regional or local
Affect modulation
Differential block - temp, sharp, light touch, motor
Forms of anesthetics targeting initial perception
Forms of anesthesia that block modulation of spinal pathway
Forms of anesthesia for blocking transmission
Forms of anesthesia for blocking transduction
Chemical compounds of local anesthetics
Benzene ring & hydrophilic amine group
- linked by amide or ester bond
Weak bases
Examples of aminoamides
Lidocaine, bupivacaine, mepivacaine, ropicavaine, prilocaine
Examples of aminoesters
Propaganda in, procaine, (novacaine) tetracain, benzocaine
Lidocaine common use
Most widely used in VM, small & large, short onset & duration of action, moderate tissue irritating
Bupivacaine common use
Longer onset & duration of action, most cardio toxic !! Second most commonly used
-consider post op analgesia effects
Mepivacaine common use
Common in horses, joint blocks, less irritating to tissues
Proparacaine common use
Ophthalmic preparations, short onset & duration
Factors effecting activity
PH at site of admin - low pH = low efficacious (cannot be in non ionized form, lower form of action)
Dose administered - better to ^ concentration than volume for prolonged action
Additives to local anesthetics
Sodium bicarbonate - reduces pain of injection
Vasoconstrictors - epinephrine- increased duration
Analgesics - opioids, alpha-2s
Toxicity of local anesthetics on cardio system
= high systemic contraction
Hypotension, arrhythmias (may be refractory) cardiac arrest
Toxicity of LA on rest p
Hypoventilation to point of apnea or resp t arrest
Toxicity of LA on CNS
Tremors or ataxia, sedation to coma, seizures
Species sensitive to LA toxicity
Cats are more sensitive than dogs
Sheep are most sensitive in general
Drugs to care for seizures from LA tox
Benzodiazepines
Drugs to care for cardio from LA tox
IV fluids for hypotension,vasodilation, positive into ropes, anti cholinergic, vasopressors
Ways to care for respt from LA tox
Supplemental ox, ventilation support
Use & function of lidocaine
Can be given IV for systemic analgesia, given as CRI
- may decreased anesthetic requirements
Most commonly used in horses
- concern for sedation & ataxia in recovery
Prokinetic GI, anti-endotoxemic, anti inflammatory
-not recommended in cats bc of cardio depression
Why is lidocaine a good option for a collcing horse?
why is lidocaine IV not recommend for cats?
Very negative ionotropic effect in cats = decreased cardiovascular function
Why are spinal needles preferred when performing an epidural ?
What types of nerves are blocked in an epidural & spinal blocks
Sensory, motor and autonomic
Blocks motor function of both legs
Spinal /sciatic blocks - singular /effected legs
Locations for epidurals
Lumbosacral or sacrococcygeal
Lumbosacral block
Common in SA
Anesthesia of caudal ab, pelvic limb, perineum, tail
Sacrococcygeal block
Common in LA could be SA
Avoids anesthesia of caudal Ab and pelvic limb
Want to avoid LA losing function of pelvic limbs
Spinal cord ends in dogs & what block is common
L5-L6
Lumbosacral
Spinal cord ends in cats & what block is common
S1-S2
Sacrococcygeal
Spinal cord ends in pigs & what block is common
L6-S1
Sacrococcygeal
Spinal cord ends in ruminants & what block is common
S3-S4
Sacrococcygeal
Spinal cord ends in EQ & what block is common
S3-S4
Sacrococcygeal
Areas effected with 0.1mL/kg of local
Perineum, tail
Area effected by 0.2mL/kg of local
Pelvic limbs, perineum, tail
Area effected with 0.3mL/kg
Caudal ab, pelvic limb, perineum, tail
Risks w spinal
Spinal requires reduces dosage, (typically half of original) if volume is too high could lead to sympathetic blockage, vasoconstriction =hypotension
CHAINS
Coagulopathy
Hypovolemia
Abnormal anatomy
Infection
Neoplasia
Sepsis
Epidural tech
LA - standing
SA - recumbent, sternal (easier) or lateral
Clip & prepare area
Palpate wings of ilium to locate space between L7 and S1
Pierce skin, bevel faces cranially, “pop” or loss of resistance - enter space
ASPIRATE
Deliver slow
hanging drop aspiration
Sucked if enters epidural space
Complications encountered
Blood during aspiration
- withdraw entirely & restart
CSF during aspiration
- remove/restart OR reduce injection volume 50%
When sternal pull hind limbs cranially, aligns pelvis
Additional pharmacologics
Analgesics- opioids, alpha 2 agonists
Prolonged compared to systemic admin
Lower doses, less side effects
Morphine is most common - alpha2 agonists more common in equine
Other types of blocks & species commonly used
Dental blocks
TAP (transverse abdominis plane) ab body wall
Bier block - distal limb, more La than Sa
Teat block - cattle, sheep
Retrobulbar block - enucleation
Lidocaine topical - feline/swine larynx prior to intubation
Proparacaine - ocular procedure, nasal tube passage (small animal)
