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NerveStimulators

NerveStimulators Barry

QuestionAnswer
All muscle relaxants act on... The neuromuscular junction.
Simply, how do muscle relaxants work? By blocking transmission across the neuromuscular junction(NMJ).
How do we differentiate the specific aspects of the action of neuromuscular agents and degree of blockade? By nerve stimulation.
Succinylcholine causes depolarization of the end plate just like... Acetylcholine.
Succinylcholine causes muscle relaxation by causing the end plate to have... Prolonged depolarization.
Non-depolarizing neuromuscular blockers bind to the acetylcholine receptor site. How does this change the receptor site? It is not able to bind to acetylcholine.
What is the most reliable method of assessing the effects of neuromuscular blocking drugs(NMBD)? A nerve stimulator.
Other than assessing the effects of our NMBD, why else do we use nerve stimulators? Locating nerves during peripheral blocks.
Nerve stimulator frequency expressed as (Hz) Hertz; which is... 1 cycle/sec, duration of 0.2 sec.
What happens if you stimulate a motor nerve with sufficient intensity? All muscles innervated by it will respond.
Why should we avoid directly stimulating the muscle fiber with a nerve stimulator? Because what we are monitoring is the inhibition of neuromuscular receptors.
Where are nerve stimulator electrodes placed? Over the course of a nerve.
Increasing block results in decreased... Response to stimulation.
How do we decrease resistance when placing nerve stimulator electrodes? Cleaning the area with alcohol, avoiding placing over scars, etc.
At the beginning of muscle relaxation therapy, it is important to get what? A baseline twitch.
What are the maintenance goals for muscle relaxation therapy? Abdominal sx: TOF 1/4. Even with TOF 2/4 or 3/4, should be able to maintain adequate relaxation with good anesthesia.
How many twitches are necessary for reversal? 1.
What is better to assess reversal, TOF or single twitch? TOF.
True or false: When choosing where to place your nerve stimulator, the facial muscles are best for assessing reversibility. False.
What are the four patterns of stimuli available on your nerve stiumlator? Single twitch, double burst, train of four(TOF), and tetany.
What frequency is single twitch usually delivered at? 1 hertz(hz).
How is single twitch used? As a control twitch, to which subsequent twitches are compared.
How is your assessment of single twitch expressed? As a percentage of control(control being your first twitch).
TOF is four successive twitches. How many hertz and how long? Four successive 0.2 sec(200milsec) stimuli in 2 sec (2hz).
TOF is expressed as... A percentage. The ratio of the responses to the 1st and 4th twitches is a sensitive indicator of non-depol neuromuscular blockade.
The twitches in TOF progressively fade as... Relaxation increases.
How does TOF respond to 100% receptor blockade? Flaccid; no responses; no TOF.
How does TOF respond to 95% receptor blockade? No twitches but diaphragm may move.
About how many receptors are blocked when you elicit one twitch on TOF? 90%. This is adequate relaxation for abdominal procedures.
Your patient has 4 twitches on TOF; VC and TV can be normal. How much of his receptors can still be blocked? 75%.
It is possible to pass inspiratory pressure test with how much receptor blockade? 50%.
What is tetany? A sustained contraction of 5sec.usually at 50 or 100 Hz.
When administering tetany, sustained contraction without fade indicates what? Adequate recovery from blockade.
What is double burst stimulation? Consists of three short high frequ. Bursts (50 Hz) separated by 0.2 msec followed 750 msec later by another three of the same.
This form of stimulation is considered the "gold standard" because it is easier to assess face than with TOF. Double burst.
Your patient has a depolarizing block on board and you've just administered double burst. What will you see? Two twitches; diminished; no fade
Your patient has a non-depolarizing block on board and you've just administered double burst. What will you see? Two twitches with fade.
True or false: an intubating dose of Succinylcholine will leave your patient still able to respond to TOF 1/4. False. This dose usually causes complete abolition of the muscle response to nerve stimulation.
How long after giving Succinylcholine before the neuromuscular junction begins to recover? 2.5 minutes.
2.5 minutes after giving Succinylcholine, when the NMJ begins to recover, what will be the response to TOF stimulation? There will be a slight but consistent response to a Train-of-Four stimulus.
2.5 minutes after giving Succinylcholine, when the NMJ begins to recover, what will be the response to tetany stimulation? A tetanic stimulus (50 per second) will produce a tetanic response of small but sustained intensity.
What happens if, 2.5 minutes after giving Succinylcholine, you administer tetany and then TOF? TOF stimulus applied after the tetanic stimulus produces a muscle response equal in intensity and character to the original series of stimuli.
True or false: with a depolarizing muscle relaxant on board, there is no tetanic fade and no post tetanic facilitation. True.
True or false: After administering an intubating dose of non-depolarizing muscle relaxant, response to TOF will usually disappear, and time to recovery depends on the agent used. True.
After giving a non-depolarizing muscle relaxant, what is response to tetany? Poorly sustained.
After giving a non-depolarizing muscle relaxant, what is response to TOF right after tetanic stimulation? Response to TOF following tetanus is increased, yet still diminishes as before.
What muscle is stimulated by the ulnar nerve? Adductor pollicis.
Where is the ulnar nerve found? Little finger side above wrist or AC area.
What muscle does the facial nerve stimulate? Orbicularis oculi.
Orbicularis oculi has similar sensitivity to NMB as what other muscles? The diaphragm and laryngeal adductors.
What does stimulation of the post tibial nerve cause? Plantar flexion of big toe.
What muscle does the mandibular nerve stimulate? The masseter muscle.
To stimulate the mandibular nerve -> masseter muscle, where would you place your electrodes? Electrode in front of and below zygomatic arch and forehead.
Which three areas have the quickest onset and recovery time from muscle relaxants? Laryngeal, abdominal, and diaphragmatic muscles.
Because it is not one of the first to recover, what is the best muscle to monitor for reversal? The adductor policis.
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