Local Anesthetics DSA Flashcards
Local anesthetics
- benzocaine
- bupivacaine
- cocaine
- dibucaine
- lidocaine
- procaine
- BBCDLP
local anesthetics chemistry
- contain hydrophilic (amine) and hydrophobic (aromatic ring)
- separated by ester or amide linkage
ester linkage duration of action
(procaine)
-more prone to hydrolysis than those with amide links (lidocaine) so have shorter duration of action
use of vasoconstrictor substances with local anesthetics
- reduces systemic absorption of agents
- useful for drugs with intermediate or short durations of action
cocaine–unique?
-intrinsic sympathomimetic vasoconstricive properties (inhibits reuptake of NE)
ester-type agents–metabolism
- metabolized in plasma
- hydrolyzed by circulating butyrlcholinesterase (plasma cholinesterase)
amide-type agents–metabolism
- hydrolyzed by liver CYP450
- toxicity can occur in patients with hepatic disease
Local anesthetics MOA
-bind reversibly to Na channels in nerves–stop spread of APs across nerve axons
local anestehtics–more potent when? examples?
- smaller and more lipophilic= faster rate of interaction with Na channel=more potent
- tetracaine, bupivacaine, ropivacaine (TBR)
local anesthetics preferentially block what fibers?
- small fibers
- myelinated nerves
- preganglionic B fibers blocked before smaller unmyelinated C fibers)
Local anesthetics preferentially block what fibers–firing frequency
-fibers that fire at higher frequencies of depolarization
Type A delta and C fibers–blocked earlier than large A alpha fibers
in bundles of large mixed nerves, what is blocked first?
-motor neurons before sensory because motor nerves are usually located circumferentially
in extremities, what is blocked?
- proximal sensory fibers are in the outer portion of nerve trunk
- distal sensory innervation is located in core of nerve
Type A fibers–diameter, myelination, sensitivity to block
- alpha (prop, motor)-12-20, heavy, +
- beta (touch, pressure)-5-12, heavy, ++
- gamma (m spindles)- 3-6, heavy, ++
- delta (pain, T)-2-5, heavy, +++
Type B fibers–diameter, myelination, sensitivity to block
Type C fibers–diameter, myelination, sensitivity to block
(preganglionic autonomic)
-
infiltration anesthesia
- directly into tissue in vicinity of peripheral nerve
- can be superficial enough to only include skin and deep enough to include intraabdominal organs
block anesthesia–into? purpose?
- into major n trunks
- anestheize a region distal to the site of injection
- (femoral nerve block for surgery distal to knee)
- brachial plexus block–UE or shoulders
spinal anesthesia
- into CSF in lumbar space
- anesthesia over a considerable fraction of body
epidural anesthesia
- into epidural space
- in sacral hiatus, or in lumbar, thoracic, or cervical regions of spine
IV regional anesthesia (Bier block)–used for?
-used for short surgical produces (
epinephrine–containing solutions–shouldnt be injected into?
- tissues supplied by end arteries (fingers, toe, ears, nose, penis) because vasoconstriction may cause gangrene
- careful when into muscle tissue–can activate B2 receptors–dilation–increase potential for systemic toxicity
local anesthetics–2 forms of local anesthetic toxicity
- systemic effects following absorption of local anesthetics
- direct neurotoxicity from local effects of these drugs when given close to spinal cord and other major nerve trunks
local anesthetics–effects on CNS–low concentration and high concentration
- low concentration–sleepiness, light headedness, visual/auditory disturbances, restlessness
- high concentration–nystagmus, muscle twitching, convulsions
- when large doses required–premedication with parenteral benzodiazepine (diazepam or midozolam) can provid prophylaxis against CNS toxicity by raising seizure threshold (local anesthetics cause depression of cortical inhibitory pathways)
- central stimulation followed by depression
local anesthetics–effects on CV system
- block Na channels, decrease electrical excitability, conduction rate, force of contraction, and arteriolar dilation–leads to systemic hypotension
- bupivacaine–most cardiotoxic (long durations of action)
