PNS Stimulator Flashcards
T/F
The Nerve stimulator is a comprehensive, all-encompassing assessment of muscle relaxation.
False
Highly subjective
prone to errors/misreading
its a tool, not the end all be all
Feeling for twitches vs. watching
feeling for the twitch is a more accurate assessment
What affects lead contact?
sweating
hair
edema/gross anasarca
wounds
anything that interferes with conduction of stimulating current
Adductor Pollicis Muscle
innervation
innervated by ulnar nerve
When stimulating the adductor pollicis muscle, we see…
thumb adduction/twitching
Which muscle group is a good indicator that upper airway muscle fxn has recovered?
Adductor pollicis muscle
thumbs UP for UPPER airway
Adductor pollicis muscles are sensitive to ___ and recovers (before/after) the diaphragm, laryngeal adductors and abd muscles.
NMB
after
T/F
If our adductor pollicis muscle TOF is 0/4, this is a good indicator the pt is no longer breathing on their own.
False
Addctr pollcs could be zero, but patient could be breathing
the addctr pollcs recovers AFTER the diaphragm, laryngeal adductors and abd muscles.
Adductor Pollicis muscle residual could indicate….
upper airway obstruction!
Do we see twitches return faster in the face or in the ulnar region?
Face twitches disappear faster, but they return quicker (than ulnar region)
Adductor pollicis lead placement
- palm up, relaxed
- leads are above ulnar nerve’s path
- black/distal lead @ level of wrist on ulnar surface of flexor crease
- second/proximal/red lead 1-2 cm more proximal; parallel to flexor carpi ulnaris tendon
Which color is the distal lead?
black
what color is the proximal lead?
red
what locations are part of facial nerve stimulation?
orbicularis oculi
corrugator supercilli
Orbicularis oculi
location
response
covers eyelid
NMB reponse similar to adductor pollicis (thumb)
eyelid squint
corrugator supercilli
location
response
covers eyebrow
similar to laryngeal adductors, but faster onset and recovery
What should we stimulate to assess good intubating conditions and profound blocks?
Eyebrows (corrugator supercilli)
(note: orbicularis oculi is better for intubation d/t its onset & recovery being more similar to the laryngeal muscles)
Cautions when using corrugator supercilli/eyebrow for TOF
it recovers FASTER than the upper airway & addctr pollicis (airway may still be paralyzed!!!)
Full twitches here do NOT indicate full strength has returned
T/F
4/4 twitches in the corrugator supercilli indicate full muscle strength has returned.
FALSE
cor.supercil recovers faster than the airway
T/F
TOF assessment is imprecise and subjective.
true
Facial Nerve lead placement
T/F
The diaphragm is (more/less) resistant to blockade. It requires ___ the dose to paralyze than the ____.
more resistant
needs 2x dose of addctr pollcs
T/F
a pt may have no twitches in thumb, but be breathing, coughing or moving their vocal cords.
True
diaphragm requires 2x the dose of paralytic to paralyze than the addctr polcs
___ and ___ are less sensitive to blocks than the adductor pollicis.
Laryngeal muscles
diaphragm
Which medication may alter the expected pattern of muscle recovery?
Succinylcholine
The face indicates when we can ___, but not when we can ___.
can indicate when to ETT
doesn’t indicate if we can ExTT
face twitches return faster than spont. breathing (laryngeal/diaphragm); pt may be apneic even if TOF 4/4 on face
T/F
Facial nerves paralyze faster but recover slower than peripheral nerves.
False
central paralyzes and recovers faster
(facial vs ulnar)
T/F
Complete recovery at the corrugator supercilli indicates full recovery at the adductor pollicis.
False
Can have full recovery of C.S. but incomplete recovery of A.P.
Posterior Tibial Nerve is good for which cases?
No access to face/arms
trauma
burns
Posterior Tibial nerve
location
response
Posterior Tibial Nerve is comparable to….
adductor pollicis (ulnar nerve/thumb)
Posterior tibial nerve lead placement
Peripheral nerve stimulator
stimulation of periph nerve and its response
Peripheral nerve stimulator delivers currents at…
0-70 miliamp (mA)
Peripheral nerve stimulator contains _________ to decrease resistance.
stimulating electrodes w/ silver-silver-chloride interface
P. Nerve stimulators use ____ current.
direct curent (DC)
current goes to and from
(instead of going in one direction)
What battery can we put in the PN stimulator?
9 volt
⭐️
T/F
The PNS is a quantitative measuring tool.
False
QUALitative
Why is the PNS assessment considered subjective and variable?
interpretation amongst providers
TOF assessment when giving succinylcholine
assess TOF after giving and before providing additional doses
Pt may have unknown pseudocholinesterase deficiency & if twitches don’t return, we won’t know what caused it
Limitation of surface electrodes
don’t always stimulate all nerve fibers
may take several mins until optimal effect
subject to resistance
-aren’t close to nerve
-improper placement
-obesity
-hair
Which has greater ability to stimulate all nerves?
surface electrodes
needle electrodes
needle
How much current and frequency can we use to asses TOF without inducing muscle fatigue?
0.1 Hz once Q10 secs
increase to brief tetanic stimulation, 50 Hz
___ Hz will cause sustained muscle contraction, known as ___. Fade will be (present/absent)
50 Hz
tetanus
no fade
Supramaximal PNS stimulation occurs at ___ Hz and causes…
> 70 - 200
muscle fatigue/fade
What contributes to the presence of fade on TOF?
muscle fatigue
(excessively high Hz and/or overly frequent TOF assessment)
T/F
Increased frequency of stimulation can restrict blood flow to the area.
False
dont spam the button
T/F
We can stimulate the nerve as desired without it affecting our assessment of block depth.
False
It can
Again…don’t spam the button
Five main patterns of stimulation
0.1 Hz means we stimulate every….
10 seconds
Which pattern of stimulation is least precise?
single twitch
Single twitch frequency range
0.1 Hz (1 stimulus every 10 secs)
1.0 Hz (1 stimulus per second)
Single twitch requirements
needs baseline comparison (perform before giving paralytic)
Can single twitch be used to determine recovery?
No
determines onset of a block but not recovery
TOF
____ stimuli @ ___ Hz
4 repetitive stimuli at 2 Hz (2/sec)
⭐️
Even with TOF 4/4, ___ receptors may be still be ____.
75%
blocked
TOF is not very accurate!
Which type of NMB agent is associated with fade in TOF?
non-depolarizing
minimum TOF to determine extubation readiness
TOFr >0.9
T4/T1
definition
fade ratio
size of fourth twitch/size of first
Fade ratio of 1.0 occurs when…
no muscle relaxant given
Fade ratio of 0 occurs when…
full muscle relaxation. (4/0 = 0; went from from 4 to 0; fully relax)
Can TOF detect a phase II block?
Yes!
Your patient’s fade ratio is 0.5. What does this mean?
first 2 twitches are equal; 50% of twitches are equal
considered partial block
bottom example in picture
T/F
TOF 3/4 twitches means the ratio is .75
No
Twitch height determines ratio, however, we cannot determine this by naked eye.
What is the TOF ratio here?
0.40 or 40%
T4/T1
What type of NMB?
nondepolarizing
What type of NMB?
depolarizing
succinylcholine (phase I)
No twitches but diaphragm might move
___% blocked
95
___% blocked
1/4 TOF w/ relaxed abd muscles
90
TOF
Pt can sustain head lift & hand grasp. What % blockage?
30
this does not guarantee pt won’t fall back asleep and become apneic
Normal VC and TV are restored at ____% blockage.
70-75
accompanied by 4/4 TOF
T/F
Fade is never exhibited with succinylcholine
False
Depends on phase
Phase II = fade
Tetanic (TET) Stimulation is a sensitive indicator to…
residual NMB
Tetanic (TET) Stimulation
how does it work?
TET fades/fatigues at (full/partial/no) block.
partial
Posttetanic Count (PTC)
helps predict with TOF twitches will return
1) 5 second, 50 Hz tetanic stimulus
2) 3 second break
3) single twitch stimuli @ 1 Hz. “PTC predicts”
One of the best ways to use TET stimulation is…
in combination with TOF to assess for residual NMB
TOF could be 4/4, but a fade on TET shows residual NMB
When should we use Posttet count (PTC)?
profound block with 0/4 TOF
“Use PTC for Profound”
PTC
Less twitches in the single-twitch portion means that…
longer time until TOF response returns
(PTC: profound block; predicts TOF return
TET: test for residual block)
PTC is used to guide ___ especially with ___.
reversal
sugammadex
What effect does the tetanus of PTC cause?
-mobilizes Ach at prejunctional membrane
-more is available at endplate to get PT (post-tetanic) twitches
Double Burst Stimulation (DBS)
Double burst stimulation (DBS) has a (greater/lesser) muscle response than TOF.
greater
In Double burst stimulation, fade is detected…
In partial blocks
-second burst
- if TOF ~0.6
What causes muscle fasciculations
-pre jxnal action of suxx
-stimulating ACh receptor on motor nerves
-repetitive firing
-release NT
recovery of Phase I block
suxx diffuses away from NMJ
metab by plasma cholinesterase
Phase II block is caused by…
prolonged exposure of suxx in NMJ (infusion, repeated dosing)
Phase I block twitches
4 equal twitches before giving and after administration
Depolarizing block is characterized by…
Decreased twitch tension
no fade on tetanic or TOF(repeated stimulation)
No post-tet potentiation
Phase I or II?
Symmetrical decreased in size of all responses to TOF
Phase I
Phase I or II?
No fade
Phase I
Phase I or II?
T4/T1 ratio is 1.0 until ALL twitches disappear together
Phase I
Phase I or II?
TOF acts like NDMR
Phase II
Phase I or II?
Fade develops in response to TOF
Phase II
Phase I or II?
results from too much/repeated depolarizer
Phase II
Which muscles face faster onset and recovery of blocks?
central muscles with good blood supply
Upper airway muscles & pharynx behave as (central/peripheral) muscles at onset. Their recovery is (fast/slow) d/t to their (sensitivity/resistance) to NMB drugs)
central
slow recovery b/c they’re sensitive to NMB drugs
ideal muscle to monitor during induction/intubation
why?
-orbicularis oculi
-more similar to central muscle
onset similar to laryngeal/diaphragm muscles
(note: the corrugator supercili is also good, but not as good b/c its onset & recovery is faster than the laryngeal muscles)
orbicularis is optimum for onset!
most valuable stimulation pattern at induction
why?
TOF
disappearance of TOF corresponds to optimal intubation conditions
(use single twitch stimulation to allow max stimulation level)
T/F
TOF 0/4 is needed for induction
False
not necessary for induction but it is for surgical conditions
T/F
Using the adductor policis for TOF during maintenance of anesthesia can indicate good diaphragm paralysis.
False
Adductor policis may be 0/4 TOF, but the diaphragm may not be paralyzed.
The diaphragm is resistant to blocks. The adductor policis is more sensitive.
Which site should be monitored during the maintenance of anesthesia?
orbicularis oculi
reflects diaphragm more closely
Most useful measurements during profound NM block
PTC and TOF
TOF should be at least ___ before administering NM antagonist
1 or 2
more is better! d/t waiting times for reversal agents to start working
during reversal and recovery, which location should be monitored?
adductor policis (peripheral muscles)
face recovers faster than diaphragm/laryngeal muscles
T/F
Head lift is considered subjective monitoring.
True
feeling and looking = subjective
hard numbers = objective
Acceleromyography (AMG)
mechanism
ulnar nerve
measure acceleration of a muscle response –> ratio
TOFR based
AMG requirements
thumb must be allowed to move (cannot tuck)
susceptible to pt movement
drugs that can potentiate NMB action (7)
antiBx (aminoglycosides)
loop diuretics (furosemide)
mag sulfate
lithium salts
Ca Ch blockers
quinidine
procainamide
CALM People Love Questions
Besides drugs, what can potentiate NMB drugs?
hypothermia
acid-base imbalance
If residual NMB is not recognized and we extubate, what could happen?
Evidence of inadequate NM recovery
T/F
Sedatives should not be used when attempting to manage an extubation in the presence of residual NMB.
False
sedatives are part of the management plan
“you may have to sedate the pt as you try to wake them up” Dr Rogers
Management of extubation w/ residual NMB
**can use LMA if pt not full stomach
