Terms in this set (70)
two categories that locals can be:
amides or esters
which type of local anesthetic has fewer undesirable effects and are more stable?
which locals are amides?
which locals are esters?
which amides has medium DOA?
which amides have long DOA?
which esters have short DOA?
which esters have long DOA?
which esters have surface action?
what is the mechanism of action for local anesthetics?
reversibly blocks neurotransmission by inhibiting the sodium channels from opening
the potency of a local is related to what?
lipid solubility and pH
why do locals start out in a neutral, lipophilic form?
crosses membrane faster
how does a local anesthetic change once inside the nerve cell?
the lower pH shifts the equilibrium toward the positively charged protonated form, which antagonizes the sodium channels more potently than the neutral form
how do <50% of local anesthetics exist when at pH 7.4?
lipid soluble, non-ionized form
what determines the lipophilic nature of a local anesthetic?
the aromatic ring and alkyl substitutions
the lipid solubility of a local anesthetic correlates to what?
its ability to penetrate through a lipid bilayer and is therefore the primary determinant of potency and DOA
local anesthetic absorption depends on what?
-addition of epinephrine
-site of administration and blood flow at the site
distribution of local anesthetics:
-lipid solubility and protein binding dictates redistribution to tissue sites
-amides are more widely distributed than esters
metabolism of amides:
-CYP 450 in liver via hydroxylation and N-dealkylation
-more complex and slower = sustained plasma concentration
-toxicity is more likely
metabolism of esters:
-hydrolysis by plasma cholinesterase
-toxicity is inversely related to rate of hydrolysis
-slowed by liver disease
which ester isn't metabolized by plasma cholinesterase?
cocaine, which is metabolized by the liver
elimination of local anesthetics:
what happens due to the poor water solubility of local anesthetics?
limits excretion of unchanged drug to <5% with the exception of cocaine
the DOA of local anesthetics is proportional to what?
the time the drug is in contact with nerve fibers
the symptoms of LA allergic reactions are usually due to what?
excessive plasma concentrations
what do excessive plasma concentrations result in?
allergic reactions to amide locals are caused by what?
allergic reactions to ester locals are most likely caused by what?
what determines systemic absorption?
-vascularity of injection site
-with or without epinephrine
-properties of the drug
ranking of high toxicity to low toxicity of administration routes:
IV > trachea > intercostal > caudal > epidural > brachial plexus > sciatic/femoral > SAB > subq
what is the progressive symptomology of systemic toxicity?
-oral numbness/tingling and metallic taste
what are the CNS effects once the toxicity levels cross the BBB?
-restlessness, vertigo, tinnitus, mydriasis
-hypotension and respiratory depression
-cardiovascular collapse and arrhythmias
max dose for lidocaine:
-4 mg/kg without epi
-7 mg/kg with epi
max dose of bupivicaine/marcaine/sensorcaine:
2.5 mg/kg with or without epi
max dose of tetracaine:
max dose of ropivacaine/naropin:
max dose of chloroprocaine/nesacaine:
how is LA toxicity treated?
-benzos for seizures
-ET tube for aspiration and hypoventilation
-fluids and vasoactive agents for hypotension and bradycardia
-lipid emulsion with Interlipid to sequester the LA
what causes caudal equinae syndrome?
compression of the spinal cord contents from diffuse injury across the lumbo-sacral plexus
what are characteristics of caudal equinae syndrome?
characteristics of methemoglobinemia?
-topical LA causes oxidation of hemoglobin to methemoglobin
-central cyanosis occurs at MetHgb >15%
how is methemoglobinemia treated?
methylene blue 1-2 mg/kg over 5 minutes
which local anesthetic is used on the eye for things like corneal transplant?
what surgical procedures are done with nasal local anesthetics?
-endoscopic sinus surgery
which locals are used for topical anesthesia of nasal procedures?
characteristics of cocaine:
-local anesthetic and potent vasoconstrictor
-dopamine reuptake inhibitor and sodium channel blocker
-euphoric high and increased energy
-risk of CV toxicity
which locals are used as topical anesthetics for the mouth, respiratory tract, and esophagus?
-nebulized 4% lidocaine
-viscous lidocaine 4%
-benzocaine (cetacaine) 2% as a nasal spray
types of mouth, respiratory tract, and esophagus procedures done with topical local anesthetics?
what is the eutectic mixture of local anesthesia (EMLA) made of?
2.5% lidocaine and 2.5% prilocaine
what procedures is EMLA used for?
-IV catheter insertion
what are the commonly used local anesthetics for local infiltration?
how do LAs spread in a peripheral nerve block?
from proximal to distal
what are the commonly used LAs for peripheral nerve blocks?
what are the common peripheral nerve blocks done with local anesthetics?
how are local anesthetics used in IV regional anesthesia?
IV local anesthetic in an isolated extremity
what is the dose of LA in IV regional anesthesia?
50 cc of 0.5% lidocaine
what are the common uses of LA in IV regional anesthesia?
-carpal tunnel resection
-minor hand surgery
what are the 2 MOA for locals in epidural anesthesia?
-diffusion across dura
-diffusion into paravertebral area
what are the commonly used local anesthetics in epidural anesthesia?
how is spinal anesthesia administered?
direct injection into lumbar subarachnoid space (CSF)
what is the principal site of action for LAs in spinal anesthesia?
parasympathetic fibers as they leave the spinal cord in the anterior rami
what is the dosing criteria for LAs in spinal anesthesia?
-desired level of anesthesia
-duration of procedure
which LAs are commonly used in spinal anesthesia?
-lidocaine no longer used in US
what can be added with the local in spinal anesthesia for a denser block?
what are transient neurologic symptoms (TNS)?
-characterized by hyperalgesia in the lower back, buttocks, and LE following uneventful SAB
-etiology is unclear
-incidence appears to be significantly higher with lidocaine
when is the ONLY time you use more than the toxic dose of a local anesthetic?
what doses of LA are used in tumescent liposuction?
5L of 0.05-0.1% lidocaine with epi in a ratio of 1:100000
what are the results of LA use for tumescent liposuction?
why is epinephrine used with local anesthetics?
-decrease systemic toxicity
-prolong local anesthesia
-decrease local bleeding, which improves visualization of surgical field
-detects whether an injection was intravascular with immediate increase in HR
how does epinephrine decrease systemic toxicity of local anesthetics?
vasoconstriction decreases blood flow to injection site which decreases uptake
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