Pharm Quiz #4 Flashcards
How does the number of twitches correlate with degree of neuromuscular block?
T4 disappears at 75% depression
T3 disappears at 80-85% depression
T2 disappears at 90% depression
Twitch suppression of 90% would equate to a TOF count of 1 or less
When is reversal of residual NMB safely achieved?
When TOF is => 3 twitches
Traditionally, it had been accepted that a TOF ratio of 0.7 or greater was an indication of adequate reversal however……..
it is now that that a TOF ratio of 0.9 should be achieved before tracheal extubation(at least 3 twitches)
Is TOF more useful monitoring depolarizers or non-depolarizers?
non-depolarizers; with depolarizers, each twitch is decreased equally in size with NO fade
What is the normal set time for tetanic stimulation?
5 seconds
In non-paralyzed skeletal muscle, tetanic response is…..
maintained tetanic contraction
Once given a non-depolarizer, the muscle shows fade and is unable to sustain muscular contraction
The degree of fade corresponds to the…..
degree of NMB
What limits the use of Tetanic stimulation?
pain
Tetanus fade is the effect of non-depolarizing agent on _____ nerve membranes.
presynaptic
With non-depolarizers, what contributes to fade during tetanic stimulation?
competitive block of presynaptic receptors that decreases mobilized and released acetylcholine
Is fade seen with tetanic stimulation during partial depolarizing block?
no
Single twitch nerve stimulations gives what information?
Post synaptic/junctional information(muscle side)
Tetanus and TOF gives what information?
Pre synaptic/junctional membranes
Tetanic stimulation should not be repeated for how many minutes?
6 minutes
*Tetanic stimulus affects NMJ of stimulated nerves for a significant time
What drug class is acetylcholine?
Quaternary ammonium ester
How many molecules are in a quanta?
1000 molecules
First twitch is only accurate if ____ seconds have elapsed since previous stimulation.
10
What is the main disadvantage of tetanus?
Post-tetanic facilitation(pain)
Increased sensitivity to non-depolarizers due to extra juctional proliferation is seen in what type of patients?
Paraplegia/quadriplegia
Greater than 30% body surface area burns acquire non-depolarizing NMB resistance. Explain
Begins 10 days after injury
Peaks at 40 days
Declines after 60 days
What are the cardiovascular effects of non-depolarizers?
Actions from histamine release
Effects at cardiac muscarinic receptors
Effects at autonomic ganglia nicotinic receptors
Rarely has clinical significance
Non-depolarizing NMB have enhanced activity due to perioperative drugs including….?
Volatile anesthetics(enhance effects) Aminoglycosides** Local anesthetics Anti-dysrhythmics Diuretics Mg++ Lithium Ganglionic blockers(arthenand)
Non-deplarizing NMB effects are altered by what?
Hypotension Acidosis/alkalosis Serum K levels Adrenocortical dysfunction Thermal injury Allergic reactions
Non-depolaring NMB enhancement is greatest with(3) and least with(2)?
Iso, Sevo, Des
Nitrous, Opioids
Non-Depolarizing NMB enhancement by VA leads to what?
probable volatile anesthetic induced depression of CNS-decreased skeletal muscle tone
By what function do Aminoglycosides enhance non-depolarizing NMB?
due to pre-junctional release of acetylcholine and decreased post-junction membrane sensitivity
Will there be any TOF or single twitches noted with profound non-depolarizing NMB?
no
With profound NMB, what is the best reversal?
time
What is the characteristics of Post-tetanic count?
5 second tetanic stimulus at 50 hz administered, followed 3 seconds later by single twitches
response seen in the early stages of recovery, before TOF reappears
After tetanic stimulus, acetylcholine synthesis and mobilization continues this leads to……
there is increased acetylcholine causing enhanced response to subsequent single twitch stimulation
number of post-tetanic twitches indicates when first twitch of TOF reappears
What is the mode of action of non-depolarizers?
Bind to post-junctional nicotinic cholinergic alpha subunit receptors sites without any activation of ion receptor channels
Is there any evidence of NMB with occupancy of < 70% of nicotinic cholinergic receptors?
No evidence of block by single twitch test
Neurotransmission fails when ___-___% of alpha subunit post-junctional nicotinic cholinergic receptors are blocked.
80-90%
What are the characteristics of non-depolarizing NMB?
- decreased response to single twitch
- fade during tetanus
- TOF ratio less than 0.7
- Post-tetanic potentiation
- potentiation of other non-depolarizing NMB
- antagonism by anti cholinesterase drugs
- NO fasciculations
Skeletal muscle response is ___ or ___.
all or nothing;
Skeletal muscle fibers contract maximally or not at all.
Therefore, when twitch response is decreased, some fibers are normally contracting & some are completely blocked.
There is no detectable block until how much of the receptors are occupied?
75-85%
Paralysis is complete at how much receptor occupancy?
90-95%
Adequate muscle relaxation corresponds to a narrow range of how much receptor occupancy?
85-90%
What is the definition of the ED95 of a drug?
dose producing 95% single twitch depression
First twitch accurate only if…….
10 seconds have elapsed since previous stimulation
Disappearance of 4th response after TOF stimulation correspond to…..
70-75% single twitch depression
With TOF, four successive stimuli are delivered at?
2 Hz every 0.5 seconds
*immediately available stores of acetylcholine are depleted and amount released by nerves decreases with successive stimuli
During _____ NMB TOF does not fade.
depolarizing
the height of all the four twitches decreases simultaneously
With non-depolarizing NMB what is the response of TOF with increasing degree of block?
- The twitches in TOF progressively fade starting with the fourth and one by one eventually disappear.
- The ratio of the height of the fourth response to the first has been defined as the TOF ratio.
- In the absence of non-depolarizing block, the T4/T1 ratio is approximately one.
There is no need for a control measurement before using TOF to measure relaxant?
true
Is there post-tetanic facilitation with TOF?
No; so can be repeated every 10 - 12 seconds
With tetanus, fade is first noted at what % receptor occupancy?
70%
What is the main disadvantage of post tetanus?
post-tetanic facilitation(very painful)
less useful than TOF
With hemiplegia, resistance to non-depolarizers develops with how many days?
2-3 days
May be due to central inhibition
Should the unaffected or affected side be monitored with those with hemiplegia?
the unaffected side
What response to non-depolorizers will be seen to those with Parkinsons and multiple sclerosis?
Normal response to NMB monitoring
Those with myotonia and muscular dystrophies have what response to non-depolarizers?
mostly normal response
What effect does succinylcholine given for intubation have on twitch suppression produced by non-polarizing NMB dosing?
increases twitch suppression even when succinylcholine effects have gone
What is the definition of autonomic margin of safety?
difference between NMB dose and dose producing circulatory effect
*ED95 dose of pancuronium producing NMB also produces increased HR, so autonomic margin of safety is low
Non-depolarizing NMB enhancement by volatile agent is caused by?
probable volatile anesthetic induced depression of CNS—>decreases skeletal tone as an additive effect
How does the co-administration of aminoglycosides effect non-depolarizing NMB function?
decreased pre-junctional release of acetylcholine & decreased post-junction membrane sensitivity to acetylcholine
reversal of non-depolarizing of NMB less predictable on patients receiving aminoglycosides
QUIZ QUESTION
Are intermediate non-depolarizers most or less expensive than succinylcholine or pancuronium?
more expensive
Do intermediate non-depolarizers have CV effects?
minimal to absent
What is the drug class of Vecuronium?
Monoquaternary aminosteroid non-depolarizer
What is the onset of vecuronium?
3-5 minutes
What is the duration of action of vecuronium?
20-35 minutes
What is the structure of vecuronium?
Structurally its pancuronium without the quaternary methyl group in the A-ring of the steroid nucleus
What is the intubating dose of vecuronium?
0.1 mg/kg
What is the physiologic effect of the absence of quaternary methyl group in vecuronium?
it reduces the acetylcholine-like character, decreasing vagolytic effects by 95%
