Peripheral Nerve Stimulator Flashcards
nerve stimulator outline (6)
1-nerve electrically stimulated
2-ach released
3-ach binds nicotinic ach R
4- ach eventually degraded
5-prejunctional ach R allow choline and acetic acid to enter nerve again
6- choline and acetic acid form ach again
how long does each stimulus last?
0.2msec (200 microseconds)
Why wouldn’t you use stimulation durations of >500microseconds?
it would have the ability to cause direct muscle stimulation
when Ach binds to nicotinic R and the R arnt blocked what happens?
twitch occurs
when Ach binds to nicotinic R and the R are blocked what happens?
weaker twitch or no twitch occurs
what is Ach degraded into?
acetic acid and choline
what plays an important role in preventing the stockpiles of Ach inside the nerve from being depleted?
prejunctional Ach R
weak muscle contraction
some of the R are blocked by muscle relaxant
zero muscle contraction
100% of R are blocked
reversing muscle paralysis with neostigmine
muscle relaxants and Ach competitively bind
junction being flooded with Ach then Ach overcomes muscle relaxant
reveral with neostigmine and there is too much muscle relaxant on board
wont be able to overcome the muscle relaxant
need some muscle function before neostigmine
reversal with sugammadex
binding and encapsulates muscle relaxant and removes it from junction
can reverse deeper levels of relaxation
what are the 5 types of nerve stimulation patterns?
single twitch train of four tetanus post tetanic count double burst stimulation
pulse duration
0.2msec
200microseconds
what are the two types of single twitch nerve stimulation
1 Hz (1 stimuation per second) 0.1 Hz (1 stimulation per 10 seconds)
describe train of four nerve stimulation
delivers 4 stimuli (0.2msec each) over 2 second period (2Hz)
what is the amount of time between stimuli for train of four
500msec
if the person is unparalyzed what will TOF show?
four twitches
tetanus
continuous nerve stimulation at 50-100Hz
floods junction with max Ach
sustained muscle contraction
what is the time limit for tetanus?
5 seconds
very painful
post tetanic count (PTC)
50Hz tetanus for 5seconds
3 second pause
single twitch stimulation at 1Hz
Double burst stimulation (DBS)
two short tetanic stimulations separated by 750msec pause
first stimulation DBS
3 impulses at 50Hz
second stimulation DBS
2 options:
two impulses at 50Hz (DBS 3,2)
three impulses at 50Hz (DBS 3,3)
fade
ocurrs when nerve is stimulated multiple times in a row and partial blockade
1st twitch stronger than 2nd
2nd stronger than 3rd
etc
what does fade mean for the ach stockpiles?
less ach is released with subsequent twitch
stockpiles are more and more depleted
muscle contraction smaller
absence of fade
equal amounts of ach released from nerve on all twitches
fade and depolarizers vs nondepolarizers
fade will occur with nondepolarizing block
fade will NOT occur with depolarizing (phase I) block
where do nondepolarizing muscle relaxants block?
presynaptic and postsynaptic Ach R
partial nondepolarizing block with fade explained
presyn Ach R blocked
choline and acetic acid cannot get back in
stockpiles diminish
less ach available for repeated stimuli
how do the stockpiles of Ach get back to normal in partial nondepolarizing block?
nerve rest for short period of time
the greater the degree of muscle paralysis (from partial nondep block) means (4)
1-higher number of presyn R blocked
2- lower amount of ach released on back to back stimuli
3- higher degree of fade
4- longer the nerve will have to rest before stockpiles refill
where do depolarizing muscle relaxants block?
postsynaptic ach R
partial depolarizing (phase I) block
choline and acetic acid can rapidly reenter
stockpiles will NOT diminish
equal amounts of Ach available for repeated stimuli
no fade observed
Will the twitches in a partial depolarizing (phase I) block be even in back to back stimulation? what about will they be the same height (strength) as before the block?
even twitches for partial
the height will be diminished when comparing before block and during block
what are the two things needed in order for fade to occur?
partial nondepolarizing block
nerve stimulated at relatively high frequency
what is the gold standard of assessment of recovery of neuromuscular blockade?
fade
If the patients fourth twitch is as strong as the first twitch what does that mean?
the patient has for sure adequately recovered from neuromuscular blockade
during the onset of a partial nondepolarizing block what will you see?
twitch height gradually decrease or fade away (TOF and single twitch)
during onset of a partial depolarizing block what will you see?
twitch height gradually decrease or fade away (TOF and single twitch)
no fade with each individual train of four pattern
during recovery of partial nondepolarizing block what will you see?
fade with TOF but not single twitch stimulation (bc single isnt fast enough frequencies to deplete stockpiles)
during recovery of partial depolarizing block what will you see?
fade patterns are not observed even with TOF
Can single twitch stimulation differentiate between depolarizing and non depolarizing blocks?
no, because the twitches gradually fade away during onset and gradually return during recovery with both depolarizing and nondepolarizing
Can TOF differentiate between depolarizing and nondepolarizing block?
yes, because it is faster you will see fade with the nondepolarizers and NO fade with depolarizers.
Can tetanus differentiate between depolarizing and nondepolarizing block?
yes, tetanus is faster stimulation so fade will be observed in nondepolarizers
Can post tetanic count differentiate between depolarizing and nondepolarizing blocks?
yes, tetanus is faster stimulation so fade will be observed in nondepolarizers
Can double burst stimulation differentiate between depolarizing and nondepolarizing blocks?
yes, double burst happens quickly enough that fade will be observed with the nondepolarizers
textbook definition of fade
nerve stimulation patterns utilized during recovery of block
When do the textbooks say that fade happens? Why?
recovery
b/c we only use nerve stimulators to assess recovery of block
what is the only nerve stimulation pattern that doesn’t detect fade or distinguish different blocks?
single twitch
What are the patterns that can detect fade and distinguish the different blocks?
TOF, tetanus, PTC, DBS
quantitative data
information about quantities (measured in numbers)
qualitative data
information about qualities (cannot be measured)
are traditional nerve stimulators qualitative or quantitative?
qualitative
are newer nerve stimulators qualitative or quantitative?
quantitative
monitor to measure how strong 4th twitch is to 1st twitch
peripheral nerve stimulator (sunmed brand) max output
70mA
1= 7mA
10= 70mA
peripheral nerve stimulator (sunmed brand) tetanus Hz max
100Hz
or 50Hz; if you open battery theres a switch
standby button
no pulse generated
How does the StimPod Quantitative stimulator work?
measures the strength of each contraction and displays it on the monitor
more accurate than qualitative
What are the two types of electrodes?
surface electrodes
needle electrodes
surface electrodes
EKG gel electrodes (may need to remove excess hair and alcojhol swab)
initial threshold is <15mA
needle electrodes
useful for conditions when unable to deliver supramaximal stimulus (obese pts)
which electrode is negatively charged?
black
depolarizing membrane
should be placed in closest proximity to the nerve
When is the charge required to deliver a supramaximal stimulus less?
when the negative electrode is placed distally
which lead should be closest to the heart (proximal)?
red
hyperpolarizing lead
how far apart should the leads be placed?
3-6cm
subthreshold stimulus
no motor units respond
threshold stimulus
one motor unit respondes
initial threshold stimulation (ITS)
submaximal stimuli
increasing number of motor units respond
maximal stimulus
all motor units respond
“pre-relaxant control response”
supramaximal stimuli
all motor units respond
Why should an anesthetist use supramaximal stimulus current?
if submaximal is applied we cant diagnose if a weak twitch is due to partial block or submax current
How to determine supramaximal stimulus?
use single twitch stimulation every 1-10 sec and increase current until max twitch observed
current required to stimulate fibers maximally
at least 40mA
could be 80mA for obese pt
What should the anesthetist do in order to ensure supramaximal current is delivered?
10-20% higher than the maximal stimulus
direct muscle stimulation
twitches would be seen but the pt could still be paralyzed
two problems with direct muscle stimulation
giving more paralytic when the pt is already paralyzed
reversing when the pt isnt ready
Why is direct muscle stimulation unlikely with our stimulators?
pulse duration is 200microseconds
max current output is 60-80mA
what are the three things that single twitch stimulation is used for?
muscle relaxant onset
supramaximal stimulus
PTC
single twitch stimulation with muscle relaxant onset order:
stimulate once every 1-10 secs before relaxant
relaxant given
twitch strength begins to fade
3 disadvantages to single twitch stimulation
no fade during recovery
cant distinguish between depol and nondepol
limited use in assessing recovery of block
assessing recovery from neuromuscular blockade with single twitch what do you do
compare max twitch height prior to muscle relaxant to max twitch height at the end of the case
2 problems with single twitch for assessing recovery
max twitch height prior to dosing MR must be obtained by eyeball
max twitch height at the end of the case could be the same and 75% of receptors could still be blocked
TOF definition
4 stimulations over 2 second period
When are patients considered “reversible” with neostigmine?
display at least 1 out of four possible muscle twitches
how many twitches are RECOMMENDED prior to neostigmine reversal?
2-3 twitches
0/4 twitches how many receptors are blocked?
> 90%
1/4 twitches how many receptors are blocked?
90%
2/4 twitches how many receptors are blocked?
80%
3/4 twitches how many receptors are blocked?
75%
4/4 twitches how many receptors are blocked?
<75%
train of four ratio definition
the strength of the first twitch compared to the strength of the first twitch
expressed as %
if the T4:T1 ratio is higher what does that mean?
the pt has stronger muscle function
What TOF ratio should be achieved before extubation
0.9
some say 0.7
at what TOF ratio does the pt have a residual neuromuscular blockade?
<0.9
What has to be used in order to obtain a TOF ratio?
quantitive nerve stimulator
3 TOF disadvantages
less useful in assessing partial depolarizing block (no fade)
not good at measuring deep levels of blockade
not as useful in onset of blockade
how long do you have to wait between TOF stimulations?
10-30 seconds
Which stimulation is good at testing deeper levels of blockade? Why?
tetanus
stimulates nerve at higher frequency and releases more Ach
2 values of tetanus
assess deeper levels of blockade
sustained tetanus >5sec withour fade for adequate reversal
a pt is profoundly paralyzed because no response to TOF or tetanus, how long until TOF twitch
will be awhile before generate TOF twitch
a pt is not profoundly paralyzed bc no response to TOF but has a response to tetanus, how long until TOF twitch
might only be a few minutes until generate twitch TOF
can tetanus differentiate between depolarizers and non depolarizers?
yes, fade is present in nondep
what is special about fade with 100Hz tetanus
fade may occur in absence of muscle relaxant from muscular fatigue
what is special about 50Hz tetanus
fade only occurs if partial neuromuscular block
degree of fade similar to TOF
PTC
may be able to be elicited even when there is no response to TOF or tetanus
mechanism of PTC
after tetanus NMJ flooded with Ach for several mins
muscle may contract even if no response to tetanus
potential to be larger than it would have been prior to tetanus
PTC: twitch before tetanus vs twitch after tetanus explain difference
twitch before: smaller contraction, less Ach
twitch after: larger contraction, more Ach
what can assess deeper levels of blockade than tetanus?
PTC
With PTC what predicts the time of recovery?
the number of visible twitches
lower #: longer time to wait
higher #: less time to wait
for intermediate duration drugs what is the time from a PTC of 1 to reappearance of twitch?
15-20 min
A what PTC twitch count should reversal with neostigmine be possible?
10 or greater
what is the purpose of a DBS?
in TOF it can be difficult for an anesthetist to detect fade with naked eye, with DBS fade is more detectable
What are the two advantages of DBS?
better indicator of fade than tetanus or TOF
less painful than tetanus
effect of the nerve stimulation on the NMJ
if nerve is stimulated faster than 1Hz the NMJ becomes temporarily flooded with Ach
what is the one stimulation that can’t flood the NMJ with Ach?
single twitch the freqency is 0.1-1Hz (too low)
the degree to which the NMJ is flooded with Ach by patterns is proportional to: (2)
stimulation frequency (higher= more Ach) stimulation duration (longer= more Ach)
Why does it matter that the NMJ can become flooded with Ach?
if the NMJ is flooded then the stimulation would produce a stronger muscle contraction
we could UNDERESTIMATE THE BLOCK
how often can DBS be repeated w/o flood of NMJ?
must wait 12-15 seconds
how often can TOF be repeated w/o flood of NMJ?
sources disagree: at least 10 seconds 12-15 seconds 15-30 seconds SO USE 10-30 seconds
how often can tetanus be repeated w/o flood of NMJ?
at least 2 minutes
how often can PTC be repeated w/o flood of NMJ?
at least 6 minutes
list recovery of muscles soonest to latest
HIGHLY TESTABLE
SOON diaphragm rectus abdominus laryngeal adductors orbicularis oculi (facial stimulation) adductor pollicis (ulnar stimulation) LATEST
what is the most useful site for determining the onset time for intubation
orbicularis oculi
because approximates the laryngeal adductors
what is the most useful site for confidence that breathing muscles have recovered?
adductor pollicis, ulnar nerve stimulus
what site is more likely to have direct muscle stimulation?
facial nerve stimulation
what is special about the median nerve?
P6 acupuncture point
reduces PONV
median nerve and PONV prophylaxis?
deliver 50mA current over median nerve single twitch stimulation 1Hz throughout
what is an alternative site to facial and ulnar stimulation?
posterior tibial nerve
When can reversal with neostigmine be given?
display at least 1/4 twitches
2-3 twitches recommended
neostigmine dose 4 twitches without fade
0-1mg
neostigmine dose 4 twitches with fade
1-2mg
neostigmine dose 2-3 twitches
2-3 mg
neostigmine dose 1-2 twitches
4-5mg
sugammadex reversal dose 4/4 with or without fade and NDMR within prev 3 hr
1mg/kg
sugammadex reversal dose 2/4 or 3/4 twitches
2mg/kg
sugammadex reversal dose 1/4 twitches
3mg/kg
sugammadex reversal dose 0/4 twitches and 1 PTC
4mg/kg
sugammadex reversal dose 0/4 twitches and no PTC
wait unless emergency
sugammadex immediate reversal dose of RSI roc dose (1-1.2 mg/kg) 3 mins after administration
16mg/kg
If neuromuscular blockade is required before the recommended wait time has elapsed (from using sugammadex) what should be used?
nonsteriodal (cisatracurium)
if 16mg/kg of bridion was used what is the minimum wait time before giving dose of roc?
24 hours for both 0.6mg/kg and 1.2mg/kg of roc
if 4mg/kg of bridion was used what is the minimum wait time before giving another dose of 0.6 roc?
4 hours
should wait >24 hr if mild renal impairment
if 4mg/kg of bridion was used what is the minimum wait time before giving another dose of 1.2 roc?
5 minutes
block may be delayed up to 4 min
duration may be shortened by 15 min
6 indicators of adequate reversal
sustained head lift 5 sec sustained tetanus 5 sec tidal volume 5-10mL/kg strong hand grip Negative inspiratory force (NIF) TOF ratio
Negative inspiratory force (NIF) definition and normal value
greatest negative pressure a pt can generate during inspiration
-50–100 cm/H2O
what is NIF measured with?
manometer
connected to ETT
what NIF is adequate for reversal of NM blockade?
-30cmH2O or more
what is the most reliable indictor of adequate reversal?
TOF ratio
TOF ratio >0.75 indicates what type of reversal?
sustained tetanus 5 sec
head lift 5 sec
NIF -25cmH2O
TOF ratio >0.9 indicates what type of reversal?
sit up unassisted and normal pharyngeal function
TOF ratio <0.9 indicates what type of reversal?
phayngeal disfunction with risk of aspiration should receive neostigmine
physiological factors that prolong duration of MR (6)
hepatic and renal disease hypothermia increased age premature neonates acidosis Myasthenia gravis
electrolyte abnormalities that prolong duration of MR (4)
hypocalcemia and hypercalcemia
hypomag and hypermag
hypokalemia
hypernatremia
medications that prolong the duration of MR (4)
antibiotics
antiarrhythmics
inhalation agents
prior administration of sux prolongs nondep
when is it possible to get fade with a depolarizing MR?
if a large enough dose of Sux is used and phase II block occurs
can you distinguish with TOF between a nondep and dep phase II?
no
when is it possible to get a phase II block?
larger than normal sux dose
infusion of sux or dosed repeatedly
mechanism of phase II dep block
unknown, possible that postjunctional membrane repolarize and there desensitized to Ach
when is tachyphylaxis seen with neuromuscular blocks?
phase II depolarizing blockade
can a phase II block be reversed?
yes with neostigmine but unpredictable response so suggested to wait until block resolves
unknown whether sugammadex would reverse (probably not)
advantages awake extubation (2)
less likely for airway obstruction or laryngospasm
airway protected
disadvantages of awake extubation (2)
coughing and bronchospasm more likely
turn over time prolonged if wake up slow
awake extubation criteria (3)
breathing spontaneously
strong enough to breathe adequately (adequate reversal)
awake enough to protect airway and avoid laryngospasm
deep extubation definition
extubates when the patient is breathing spontaneously but ~1MAC
advantages of deep extubation
less likely to cough or bronchospasm
dont have to wait for pt to wake up turnover is faster
when is deep extubation preferred?
hernia surgery
nasal septoplasty
tonsillectomy
disadvantage to deep extubation (3)
airway not protected
airway will obstruct (always need nasal or oral airway)
laryngospasm still possible
deep extubation criteria (3)
breathing spontaneously with adequate tidal volumes
must be truly deep
thoroughly suctioned (prevent laryngospasm)
how can you test if a patient is truly deep?
no cough with ETT cuff deflation
absence of reaction with forceful jaw thrust
deep extubation absolute contraindication (4)
full stomach
GERD/hiatal hernia
difficult airway/intubation
airway edema
deep extubation relative contraindications
obesity
patients with OSA
post extubation hypoxia possibilities (6)
apnea bronchospasm atelectasis pulmonary edema inadequate reversal hypoventilation/oversedation
if you followed extubation criteria what is the most likely cause of post extubation apnea? effective initial treatment?
obstruction or laryngospasm
jaw thrust/oral/nasal airway
treatment of airway obstruction/laryngospasm (4)
1-jaw thrust with mask
2- jaw lift with mask and oral airway
3-gentle positive pressure and oral airway
4- LMAvs propofol and sux
(you go up the steps if the first one doesn’t work)
diagnosis of bronchosparm
auscultation (wheezing)
treatment of post extubation bronchospasm
breathing treatment
epi if severe and nonresponsive to breathing treatment
diagnosis of atelectasis
auscultation (diminished breath sounds)
chest xray
treatment for atelectasis post extubation
Bi-level positive airway pressure (BiPAP) mask
BiPAP definition
continous positive pressure but higher during inspiration to open alveloi
when is BiPAP indicated?
OSA and atelectasis
What makes BiPAP better than CPAP
reduced air trapping and easier exhalation compared to CPAP
What can BiPAP be performed with?
ETT or facemask
diagnosis of pulmonary edema
auscultation (crackles)
chest x ray
treatment of pulmonary edema post extubation
diuretics (if cause is fluid overload)
possible intubation vs pressure support ventilation
