midterm - 2 Flashcards
If admin of LA and it gets systemc effects and depressing the CNS it actually is considered a _
anything depressing the CNS is considered a GENERAL ANESTHETIC
the first general analgesic
cocaine
pH-pKa -5 -4 -3 -2 -1 0 1 2 3 4 5
about how much A- (base form, nonionized form)
about how much A-(base form) -5 = 0.001% -4=0.01% -3=0.1% -2= 1% -1=10% 0=50% 1=90% 2=99% 3=99.9% 4=99.99% 5=99.999%
if pKa is around 7 - we have both forms in solution
the pH-pKa is important because it is essential that LA crosses the neuronal membrane
_ form crosses the membranes
_ form once inside that blocks axonal conduction
basic form (uncharged) to cross membranes
acidic form once inside to block
so we need both forms and they have to be in equilibrium
Local anesthetics are _ class. At physiological pH(7.4) they are in equilibrium so that both the basic form and the acid form are represented Basic form crosses membrane Acidic form blocks Na+ channels
Amides
general structure of LA
aromatic group
ester or amide linkage
amine group(primary, secondary,tertiar)
quaternary none of these bc permanent postive charge and can’t cross membrane
generally secondary and tertiary amines are used
general structure of LA
the _ group renders the LA lipophilic
aromatic group
ring structure
esters vs amides
_ linkage will by hydrolyzed by pseudocholinesterase and have very short 1/2 life
_ linkage will be METABOLIZED by P450 enzymes in the live, longer half life in plasma
esters - pseudo and short 1/2
amides - liver P450 - longer 1/2 life
_ will have an “i” in their name somewhere prior to “caine”
_ will not
amides - I 0 lidocaine
esters - no i prior to caine - procaine
why are we worried about esters in LA
esters are generally more allergenic
not particularly worried about short 1/2 life
1-6 sensations blocks (nerves fiber types) relative sensitivity to LA
- pain - unmyelinated c fibers
- cold
- warmth
- touch
- deep pressure
- motor
recovery in reverse order
Unmyelinated pain C - most sensitive to local, stay block the longest
Motor nerves - hardest to block, easiest and fastest to come back
LA bind to the _ form of the sodium channel, they produce a more rapid nerve block on axons with a _ firing rate
bind to the OPEN form of Na channel
more rapid nerve block on axons with a more rapid firing
Peripheral nerves consist of bundles of nerve fibers encased by _
epineurium
perineurium
endoneurium
Connective tissue
fxns served by B and C fibers are more readily disrupted by LA than the _ fxns of _ fibers
motor fxns of A fibers
A delta - sharp pain
activity at several nodes of Ranvier must be blocked to achieve total nerve block
requires longer diffusion distance and larger diameter
_ LA (amide) would be favored for epidural anesthesia during childbirth (maintain uterine muscle contractility)
bupivacaine
