local anesthetics nagelhout Flashcards
T/F Myelinated nerves are larger, conduct impulses faster, and are more difficult to block with local anesthetics than are unmyelinated nerves.
TRUE
what are the two opposing forces that influence K movement into and out of the neuron?
a concentration gradient pushes K outward. an electrostatic gradient, created by the impermeability of the membrane to cations, tends to keep the K in the cell.
local anesthetics bind to the ___ and ___ states, but not the ___ state
open and inactivated.
not the closed
what is the order of differential blockade?
autonomic, superficial pain, touch, and temp, motor function, and proprioception
the ___ fibers are the largest in diameter and most heavily myelinated
A
which fibers have the fastest conduction velocity?
Alpha
the __ fibers, which conduct pain and temp impulses, are the smallest of all fibers.
C
T/F C fibers are myelinated
FALSE.
The small, unmyelinated C fibers are more or less resistant to blockade than the larger A delta or B fibers?
MORE
diffusion across the membrane is influenced by what three factors?
PKA, concentration of local anesthetic, ph of surrounding tissue and nerve fiber
which part of the structure provides lipophilic characteristics?
aromatic ring
which part of the structure provides hydrophilicity to the molecule?
tertiary/ quaternary amine
what is the major difference among local anesthetics chemically/
the major diff is in their ester or amide linkage that binds the aromatic ring to the amine group
how can you tell if a drug is an amide?
has 2 letter i’s in the name
how are esters metabolized?
catalyzed by plasma and tissue cholinesterase via hydrolysis, occurs throughout the body and is rapid
how are amides metabolized?
in the liver by cyp1A2 and cyp3A4 (and thus a significant blood level may develop with rapid absorption)
which class has a higher allergic potential?
esters.
ester drugs are long or short acting? why
esters are shorter acting d/t their metabolic, tetracaine is the longest acting ester
amides are short or long acting? why
amides are longer acting bc they are more lipophilic and protein bound and require transport to the liver for metabolism
the higher the concentration of drug injected into the area of nerve or nerves to be blocked, the ___ the onset of action. if multiple nerves are being blocked, a ____ intensity might also be evident.
faster, greater
Systemic absorption away from the deposition site results in the ___ and ___ of the drug effect, rather than the ___ as with most other drugs.
offset & termination. rather than onset
what are the factors that influence duration of action?
factors that affect absorption such as vascularity and blood flow of the injection area, lipid and protein binding, and addition of vasoconstrictors
Increased lipid solubility correlates with ___ protein binding, ____ potency, ____ DOA, _____ tendency for severe cardiac toxicity
increased, increased, longer, higher
LA’s are ___ (strong/weak) _____ (acid/base)
weak base
LA’s bind mainly to ____
a1-acid glycoprotein
secondary binding to albumin also occurs
the more ___ LA is, the slower it will penetrate a nerve
ionized
because their ionization is less, LA’s with lower pKa (7.6 to 7.8) such as lidocaine, mepiviacine, and prilocaine tend to have a ___ onset of action than drugs with a greater pKa (8.1 to 8.6). the exception to this is _____
rapid
chloroprocaine
the closer to pka is to 7.4, the more __ the onset
rapid
T/F the total dose of LA rather than the volume or concentration linearly determines the peak plasma concentration.
TRUE.
volume doesn’t matter - dose does
does using epi increase or reduce the risk of systemic toxicity of LA?
reduce.
what does the addition of bicarb do to local anesthetics
it increases the non-ionized portion of the drug which facilitates the drug’s passage across the neuronal membrane and speeds onset. it also prolongs the duration and reduces pain on injection
what are the 3 major factors contributing to the negative chronotropic and inotropic effect’s of LA’s?
hypoxia, hypercarbia, acidosis
In adults, the subarachnoid space extends from the foramen magnum to __ and extends to ___ in children.
S2, S3
The spinal cord itself extends to __ in adults and __ in children.
L1, L3
during a spinal, the first pop is the needle penetrating the ____ and the second is ___
lig flavum, dura mater
what is the specific gravity of CSF?
1.003 to 1.008
acidosis ___ plasma protein binding, which ____ the free form of the drug in the bloodstream, which results in ___ amt available for diffusion in the brain
decreases, increases, increases
the standard concentration of epi added to a local anesthetic to prolong the duration of an epidural block is __mcg/ml, which represents a _:_____ solution
5 mcg/ml, 1:200000
the addition of epi to what drugs significantly affects duration of action?
mepivacaine, lidocaine..
all locals cause vasodilation except for which 3?
cocaine, lido, ropivacaine
what are the two principal determinants of the duration of action of a spinal
the anesthetic drug used and the total dose given
which locals are associated with the highest risk of allergic reaction?
esters - procaine, cholorprocaine, tetracaine, benzocaine… PABA, patients have previous exposure in lotions sunscreens cosmetics etc
what things added to a LA makes it hyperbaric
dextrose.
sterile water makes it hypobaric
0.1 to 0.2 mL of 1:1000 (1 mg/mL) epinephrine is the dose typically added to the local anesthetic to prolong the duration of the spinal.
learn how to divide these out………
mechanism of action of LA’s
Local anesthetics bind to the alpha-subunit on sodium channels on the inside of the cell membrane and block the large influx of sodium into the cell associated with depolarization.
which needles reduce the incidence of PDPH
24-27g pencil point needles
what landmark it T4 associated with
superior aspect of the iliac crest
what is most important in terms of onset/
ionization- the charged or ionized form of a drug does not penetrate membranes well
what is the MOA of bicarb in theory?
addition of bicarb increases the ph of the PA resulting in the presence of more drug in the non-ionized state. this form of the drug readily diffuses across cell membranes, therefore speeds onset
explain ion trapping in the fetus
fetal ph is lower than maternal ph which may result in high fetal levels of LA
why is injecting local into an acidic environment ineffective
because the loss of lipid solubility prevents absorption into the nerve, therby preventing access to the site of action
which ester has a slow metabolism
tetracaine
hepatic clearance is a function of ___ and __ and is the primary factor that determines the rate of elimination of ___ LA’s
hepatic extraction ration and hepatic blood flow… amides
what 2 LA’s cause methemoglobinemia?
benzocaine and procaine
nagel also says prilocaine bc of its metabolite
what 2 are in the eutectic mixture
lidocaine and prilocaine
