Local Anesthetics Flashcards
What classes of nerve fibers are myelinated?
A and B
What are the fastest nerves to block?
myelinated and small
What nerve class represents the sympathetics?
B (preganglionic sympathetics)
What is the function of C fibers?
visceral pain (unmyelinated)
What are the 4 functions of A fibers?
1) motor (alpha)
2) tactile, proprioception (beta)
3) muscle tone (gamma)
4) pain, cold temp (delta)
What is the rank order of the fastest nerve types to block?
symps > sensory > motor
What are the 3 stages of the sodium channel gate?
1) resting
2) open
3) inactivated
Define frequency dependent blockade?
local anesthetics preferentially bind inactivated and open states rather than resting (want M open)
What is the name of the local anesthetic binding site?
R
What are the two molecular classes of anesthetics?
1) amides (2 i’s in the name. Ex: Lidocaine)
2) esters (1 i in the name. Ex: cocaine)
True or false: binding occurs on the cytoplasmic side of the receptor?
TRUE (R site)
only uncharged can get thru
What determines the onset time of local anesthetics?
pH and pKa (why given with sodium bicarb a lot)
What determines the potency of LAs?
lipid solubility
What determines the duration of LAs?
protein binding
What are 2 adjuncts given with LAs?
1) epinephrine (used for vasoconstriction - keeps the drug in the neighborhood for drugs that vasodilate - not helpful for drugs that are protein bound)
2) alpha 2 agonists
What is the only LA that can be used IV?
lidocaine
What is an indication of neuraxial anesthesia?
surgery at chest or below
What is the main difference between a spinal and epidural block?
spinal: drug deposited at L3-L5
epidural: any level, site of action is nerve roots (more targeted)
What are the cardiovascular effects of neuraxial anesthesia?
bradycardia (unopposed vagal stim since you block symps)
What are the 4 factors that absorption depeneds on?
1) vascularity (ICNB > caudal > epidural > brachial plexus > sciatic) 2) props of durg 3) props of patient 4) addition of vasoconstrictos
How are esters eliminated?
plasma cholinesterase
How are amides eliminated?
liver
Do you give more or less drug when combining it with epi?
MORE
What drug is NOT ok to use to treat arrhythmias?
lidocaine
What is a specific therapy for toxicity of LAs?
intralipid (creates a sink that LA can be sequestered into)
