Pathophysiologic Implications - NMB Flashcards
What does it mean when you have RESISTANCE to a nondepolarizing NMB?
you will have to give more of the medication to get the response wanted
what does it mean when you are sensitive to a NMB?
your duration will last longer if you give the normal dose, so give less
What does phenytoin (dilantin) due to a nondepolarizing NMB?
- causes shorter duration (resistance)
- Because of
- decreased activity of AChE
- induced cytochrome p450 in the liver (metabolism)
- increased number of ACh sites
- can change duration even if you give it intraoperatively!!
There are 3 meds mentioned that phenytion causes a decreased duration of. What are the meds and the percentages associated?
Rocuronium 20%
Vecuronium 37%
Pancuronium 40%
These meds are given to myesthenia gravis patients (immunosuppressed pt, asthma) to improve neuromuscular function; chronic use has been reported to cause ____ to _____ NMB like vecuronium
resistance, steroidal
these two meds inhibit phosphodiesterase which increases cAMP needed to synthesize and release ACh which leads to more ACh
- aminophylline and theophylline
- a greater dose is needed to compete with the increase in ACh
This med in large doses, 1-4 mg/kg, inhibits phosphodiesterase which increases cAMP which makes ACh more available
furosemide
-increase the dose due to increased resitance
resistance begins 10 days after injury, peaks at 40, and declines after 60 days (463 days is longest)
burn injuries
- would not give depolarizing bc K
- due to a decreased sensitivity of the postjunctional receptors to either ACh or nondepolarizing NMB, basically nondepolarizers will be chewed up
Type of patients with increased extrajunctional receptors?
MS, hemiplegic limb, CVA, prolonged immobilization, massive trauma
Why is the paralyzed limb of a CVA patient more resistant to NMB?
more extrajunctional cholinergic receptors due to denervation
Main reason not to give MS patients NMB?
they are unpredictable! Do not know if pt are in remission periods.
definitely not going to give SCh bc of hyperkalemia
this causes increased resistance due to decreasing the resting potential of the membrane which increases the positivity of the cell
chronic hyperkalemia
does chronic hyperkalemia increase or decrease sensitivity to SCh?
increases sensitivity because the resting membrane potential is more positive, which is closer to depolarization and closer to an action potential
pharmacologic -corticosteroids -amino/theophylline -furosemide burn injuries increased extrajunctional receptors chronic hyperkalemia
factors associated with resistance
these decrease the skeletal muscle tone and decrease the sensitivity of muscle membranes to depolarizations lower than the ED95; have the greatest impact on long acting NMB (pancuronium)
volatile anesthetics
increase sensitivity
these interfere with the release of ACh from the prejunctional receptors, block ion channels, and directly depress skeletal muscle tone
local anesthetics
increase sensitivity
these cause a magnesium type effect to decrease release of ACh to make reversal unreliable (can give Ca)
antibiotics
increase sensitivity
aminoglycosides - gentamicin, neomycin, streptomycin, kanamycin, amikacin, tobramycin
antibiotics that increase the sensitivity of nmb
antibiotics that have NO effect on nmb
penicillins, cephalosporins, erythromycin
when given to a patient who is recovering from a nondepolarizing nmb, the block is potentiated by the blockage of the prejunctional release of ACh
lidocaine
increased sensitivity
potentiates nondepolarizing nmb and SCh
quinidine
this med has a variable effect on nondepolarizing and prolonged onset and duration of depolarizing nmb
lithium
increased sensitivity
what production is decreased when giving <1mg/kg of lasix per day resulting in increased sensitivity to nmb
lasix
this med increases the sensitivity of nmb (specifically atracurium and vecuronium, and is used for renal replacement pt, rheumatoid, and psoriasis pt
cyclosporine
this med reduces the dose required due to membrane desensitization causing enhanced, but not prolonged, blockade by nondepolarizing nmb
succinylcholine
if you have a combination of nondepolarizing nmb - you will see a ___ effect
synergistic
-usually combo of drugs from different classes
the usual site of action is on the slow channels, not fast channels like the postjunctional receptors so unpredictable effects have been reported
calcium channel blockers
acute admin of this med may potentiate nondepolarizing nmb
-the combo of the two types of meds could cause critical illness myopathy
hydrocortisone
this med is given as a stress dose to people on chronic steroids
hydrocortisone
these meds can decrease sensitivity of the muscle membrane to cause relaxation of its own and potentiate nondepolarzing nmb
trimethaphan and hexamethonium
these meds inhibit plasma cholinesterase activity to cause prolongation of depolarizing block
trimethaphan and hexamethonium
ganglionic blockers
prolongs duration by slowing clearance via hepatic enzymes, renal pathways, hofmann elimination, and ester hydrolysis
hypothermia
antihypertensives hydrocortisone ca channel blockers SCh cyclosporine lasix lithium lidocaine quinidine antibiotics volatile and local anesthetics
pharmacologic factors associated with increased sensitivity
increases membrane potential (hyperpolarization) and increases sensitivity to nondepolarizing nmb (resistant to SCh)
acute hypokalemia
decreased release of ACh from prejunctional receptors which causes an enhanced block (think pregnant women and preterm labor)
hypermagnesium
___ causes decreased volume of distribution of nmb so more drug reaches the receptors
dehydration, seen with hypernatremia
difference in muscle mass from men cause __ block in women with similar mg/kg
(really not clinically relevant)
greater
chronic autoimmune disorder caused by a decrease in functioning acetylcholine receptors at the NMJ by antibodies
myasthenia gravis
treatment of myasthenia gravis includes anticholinesterases and immunosuppressive drugs. More ACh is available which causes
resistance to nondepolarizers and sensitivity to SCh
what muscles are first to show fatigue, weakness in undiagnosed myasthenia gravis
ocular, pharyngeal, and laryngeal muscles
with these patients it is very important to get a baseline TOF and reduce the dose by 1/2 or 1/3
myasthenia gravis because they may become weak with even 1/10 of the normal intubating dose!!
prob shouldn’t use nmb
seen with oat cell carcinoma of the lung; autoimmune disease where presynaptic calcium channels are destroyed by antibodies
myasthenic syndrome - eaton lambert
sensitive to both nondepolarizing and SCh
myasthenic syndrome - eaton lambert
normal or possible prolonged effect of nondepolarizing nmb when muscle weakness, atrophy, exists
muscular dystrophy
SCh causes prolonged contraction but nondepolarizing blockades have a normal response
myotonia dysrophica
a degenerative disease of motor ganglia in the anterior horn of the spinal cord and spinal pyramidal tracts that causes skeletal muscle atrophy and weakness
amyotrophic lateral sclerosis
what does als cause
prolonged response to nondepolarizing nmb (sensitivity) and hyperkalemia with SCh
have a different volume of distribution which makes the dose less concentrated
“water babies”
pediatric population
vecuronium onset is quicker in infants and children due to ____ times
faster circulation
infants and neonates have prolonged recovery to vecuronium because .. while children have a faster recovery
liver function isnt as good
neonates require __ lower dose by weight due to increased sensitivity when given atracurium
25%
special considerations for the elderly, dried up little old people
- decreased total body fluid, fat, lean muscle
- decreased plasma protein, CO, kidney/liver function
- priming technique causes rapid desat
- basically more free drugs floating around
even though this nmb is age and organ independent, the histamine release was found to be greater because of increased exposure to things
atracurium
these two nmb cause no significant difference in duration or sensitivity to the elderly
pipecurium and mivacurium
no difference in onset time but prolonged recovery with this nmb in the elderly mainly due to decreased liver/kidney function
rocuronium
with this nmb, recovery times are prolonged in obese pop so dose based on ideal body weight
vecuronium
there is no significant difference with this nmb in the obese pop
atracurium
dose this nmb based on ideal body weight in the obese pop
roc
due to plasma cholinesterase, dose with drug based on total body weight in the obese pop
SCh
what measurement matters in ideal body weight?
height
if this is given prior to admin of recuronium, you will see a decreased onset time (works faster)
ephedrine because it increases HR and CO so gets to site faster
if this is given prior to admin of rocuronium, the onset time was increased by 26%
esmolol because of decreased CO, EF so took longer to travel to sites
