Lecture 07_Fall Flashcards
Of the three types of nerve fibers (A,B,& C) ___ nerve fibers are the smallest and slowest and __ are the biggest and fastest.
C nerve fibers are the smallest and slowest and A are the biggest and fastest.
The action of local anesthetics includes loss of ____, ____, and ___ function
sensory, motor, and autonomic
Which nerve fibers are responsible for pain and cold temperature?
A-delta, and C
How do LAs work?
They enter the cell and bind to voltage-gated Na channels, prevent the influx of Na, which slows conduction
Which fibers are unmyelinated?
only C fibers (Sensory - dull pain, temp, touch)
What is the sequence of the differential blockade?
Autonomic -> Sensory -> Motor
B->C->A
Nerve fibers are surrounded by ____ and bundled into _____ which are surrounded by _______. ____ are groups of fascicles are surrounded by ______.
endoneurium, fascicles, perineurium, Axons, epineurium
LAs bind at the ____ in between myelinated segments
nodes
Do LAs have faster onset with myelinated or non-myelinated fibers?
myelinated
Do LAs have faster onset with small fibers or large fibers?
small
T or F. Recovery from LAs is usually in the opposite order of onset.
True.
Usually you lose B
(Autonomic) -> C (Sensory) -> A (Motor)
And they return in the opposite order:
A (Motor) ->C (Sensory) -> B (Autonomic)
List the order you lose your senses in with a local block.
Temp (cold -> hot) -> pain -> touch -> deep pressure -> proprioception
_ fibers are mostly motor, _ fibers are mostly autonomic, and ___ fibers are mostly sensory
A, B, C
Local anesthetics are weak ____ that become charged by accepting a proton on the _____.
Bases, amine
What are the two groups of LAs?
Esters and Amides
How does an acidic environment effect the onset of LAs?
Acidic environment -> more charged species -> slower onset
Onset of action of LAs depends on ___, ___, and ___.
lipid solubility, charge, and size.
Systemic absorption of local anesthetics is proportional to ____ and inversely proportional to ____.
vascularity, vasoconstriction
T or F. EMLA cream can cause methemoglobinemia.
true
EMLA cream is lidocaine and prilocaine
Although LAs primarily bind to ___ channels, they may bind to ___, ___, and ___ channels as well.
Although LAs primarily bind to Na channels, they may bind to K, Ca, and NMDA channels as well.
LAs are made up of a benzene ring, link and amine group. Which part of this structure indicates whether it is an ester or amide?
the link is either an ester or an amide
T or F. LAs block the smallest nerve fibers first/most.
False - it depends on myelination. Myelinated fibers may actually be more sensitive to LAs than non-myleinated fibers.
T or F. LAs with a pKa closer to physiologic pH will have a faster onset.
True. LAs with a pKa closer to physiologic pH will have a faster onset because the concentration of nonionized form is higher - and that is the form that is lipid soluble
The density of a block depends on ___ and ___.
concentration and volume
Duration of LA action correlates with ____.
lipid solubulity
Place the following areas in order (from greatest to least) for systemic absorption of LAs
peripheral nerves, tracheal, caudal/epidura, IV, subcutaneous, intercostal
IV > tracheal > intercostal > caudal/epidural > peripheral nerves > subcutaneous
What effect does adding epi to LAs have? What about NaHCO3?
Adding epi will decrease the amount of systemic absorption because it causes vasoconstriction, but it also makes the environment more acidic which will slow the onset of action.
If you also add bicarb, it will speed the onset of action. With the combination of the two, you will improve the quality of the block and prolong the duration of blockade.
Which areas of the body should use of epi in the LA be avoided?
fingers, toes, penis, nose
What is the only LA that causes vasoconstriction?
cocaine
Is metabolism of ester or amide LAs faster? How are they each metabolized?
Esters are faster - they are rapidly metabolism by pseudocholinesterase (ester hydrolysis)
Amides - Metabolized in liver – much slower than with esters
T or F. There is no pseudocholinesterase in CSF and therefore the duration of a block with ester LAs and the termination of action depends on their absorption into the bloodstream.
true
Why is it important to know if your patient has abnormal pseudocholinesterase activity?
They would be at increased risk of LA toxicity with ester LAs
Which group of LAs (esters or amides) is an allergic reaction more common? Which 2 LAs in that group is it most common with?
Esters. Esters are derived from PABA – can be allergic to the production of this metabolite
Procaine/benzocaine -> PABA -> allergic reaction
What are the CNS signs of LA toxicity?
Circumoral / tongue numbness, dizziness, tinnitus, blurred vision
Restlessness, agitation, nervousness, slurred speech, drowsiness, loss of consciousness
Muscle twitching, seizures
How do you treat the CNS signs of LA toxicity?
Treat with benzodiazepines (caution with thiopental, propofol)
cauda equina syndrome is associated with what?
Repeated doses of intrathecal lidocaine or tetracaine
What is TNS and what is it associated with?
TNS (transient neurologic symptoms) with intrathecal 5% lidocaine - Slight to severe pain in buttocks and legs starting within 24 hours after anesthesia, lasting up to 10 days
What are the Cardiovascular signs of LA toxicity?
Depress contractility, automaticity, conduction velocity
Also causes smooth muscle relaxation -> hypotension - Can lead to cardiac arrest
How do you treat cardiovascular signs of LA toxicity?
Treat: ACLS, pressors - Avoid lidocaine, limit epi -
Intralipid to reverse cardiotoxicity - May require CPB (bypass)
Which LA is considered most cardiotoxic?
IV bupivacaine – it avidly blocks cardiac Na
channels – difficult resuscitation
Can also cause vasodilation and inhibition of sympathetic reflexes
Methemoglobinemia: Most common with ___ or ___ metabolites, but possible with ____.
prilocaine or benzocaine but possible with lidocaine
What symptoms indicate met-Hgb >10%?
shortness of breath, cyanosis, mental status changes, headache, fatigue,
dizziness, loss of consciousness
What symptoms indicate met-Hgb >50%?
dysrhythmias, seizures, coma and death
What is used to treat methemoglobinemia?
methylene blue
Symptoms of methemoglobinemia are more common in patients with what comorbidities?
anemia, cardiovascular disease, lung disease, sepsis, or other Hgb abnormalities hemoglobin species
What is the max dose of marcaine?
Marcaine = Bupivacaine
Max dose in (mg/kg)
2 w/o epi
3 w/ epi
What is the max dose of lidocaine?
Max dose in (mg/kg)
4.5 w/o epi
7 w/ epi
What is the max dose of Naropin?
Naropin = Ropivacaine
Max dose in (mg/kg)
2 w/o epi
3 w/ epi
