Peripheral Nerve Stimulator Flashcards
1
Q
nerve stimulator outline (6)
A
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
2
Q
how long does each stimulus last?
A
0.2msec (200 microseconds)
3
Q
Why wouldn’t you use stimulation durations of >500microseconds?
A
it would have the ability to cause direct muscle stimulation
4
Q
when Ach binds to nicotinic R and the R arnt blocked what happens?
A
twitch occurs
5
Q
when Ach binds to nicotinic R and the R are blocked what happens?
A
weaker twitch or no twitch occurs
6
Q
what is Ach degraded into?
A
acetic acid and choline
7
Q
what plays an important role in preventing the stockpiles of Ach inside the nerve from being depleted?
A
prejunctional Ach R
8
Q
weak muscle contraction
A
some of the R are blocked by muscle relaxant
9
Q
zero muscle contraction
A
100% of R are blocked
10
Q
reversing muscle paralysis with neostigmine
A
muscle relaxants and Ach competitively bind
junction being flooded with Ach then Ach overcomes muscle relaxant
11
Q
reveral with neostigmine and there is too much muscle relaxant on board
A
wont be able to overcome the muscle relaxant
need some muscle function before neostigmine
12
Q
reversal with sugammadex
A
binding and encapsulates muscle relaxant and removes it from junction
can reverse deeper levels of relaxation
13
Q
what are the 5 types of nerve stimulation patterns?
A
single twitch train of four tetanus post tetanic count double burst stimulation
14
Q
pulse duration
A
0.2msec
200microseconds
15
Q
what are the two types of single twitch nerve stimulation
A
1 Hz (1 stimuation per second) 0.1 Hz (1 stimulation per 10 seconds)
16
Q
describe train of four nerve stimulation
A
delivers 4 stimuli (0.2msec each) over 2 second period (2Hz)
17
Q
what is the amount of time between stimuli for train of four
A
500msec
18
Q
if the person is unparalyzed what will TOF show?
A
four twitches
19
Q
tetanus
A
continuous nerve stimulation at 50-100Hz
floods junction with max Ach
sustained muscle contraction
20
Q
what is the time limit for tetanus?
A
5 seconds
very painful
21
Q
post tetanic count (PTC)
A
50Hz tetanus for 5seconds
3 second pause
single twitch stimulation at 1Hz
22
Q
Double burst stimulation (DBS)
A
two short tetanic stimulations separated by 750msec pause
23
Q
first stimulation DBS
A
3 impulses at 50Hz
24
Q
second stimulation DBS
A
2 options:
two impulses at 50Hz (DBS 3,2)
three impulses at 50Hz (DBS 3,3)
25
fade
ocurrs when nerve is stimulated multiple times in a row and partial blockade
1st twitch stronger than 2nd
2nd stronger than 3rd
etc
26
what does fade mean for the ach stockpiles?
less ach is released with subsequent twitch
stockpiles are more and more depleted
muscle contraction smaller
27
absence of fade
equal amounts of ach released from nerve on all twitches
28
fade and depolarizers vs nondepolarizers
fade will occur with nondepolarizing block
| fade will NOT occur with depolarizing (phase I) block
29
where do nondepolarizing muscle relaxants block?
presynaptic and postsynaptic Ach R
30
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
31
how do the stockpiles of Ach get back to normal in partial nondepolarizing block?
nerve rest for short period of time
32
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
33
where do depolarizing muscle relaxants block?
postsynaptic ach R
34
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
35
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
36
what are the two things needed in order for fade to occur?
partial nondepolarizing block
| nerve stimulated at relatively high frequency
37
what is the gold standard of assessment of recovery of neuromuscular blockade?
fade
38
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
39
during the onset of a partial nondepolarizing block what will you see?
twitch height gradually decrease or fade away (TOF and single twitch)
40
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**
41
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)
42
during recovery of partial depolarizing block what will you see?
fade patterns are not observed even with TOF
43
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
44
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.
45
Can tetanus differentiate between depolarizing and nondepolarizing block?
yes, tetanus is faster stimulation so fade will be observed in nondepolarizers
46
Can post tetanic count differentiate between depolarizing and nondepolarizing blocks?
yes, tetanus is faster stimulation so fade will be observed in nondepolarizers
47
Can double burst stimulation differentiate between depolarizing and nondepolarizing blocks?
yes, double burst happens quickly enough that fade will be observed with the nondepolarizers
48
textbook definition of fade
nerve stimulation patterns utilized during recovery of block
49
When do the textbooks say that fade happens? Why?
recovery
| b/c we only use nerve stimulators to assess recovery of block
50
what is the only nerve stimulation pattern that doesn't detect fade or distinguish different blocks?
single twitch
51
What are the patterns that can detect fade and distinguish the different blocks?
TOF, tetanus, PTC, DBS
52
quantitative data
information about quantities (measured in numbers)
53
qualitative data
information about qualities (cannot be measured)
54
are traditional nerve stimulators qualitative or quantitative?
qualitative
55
are newer nerve stimulators qualitative or quantitative?
quantitative
| monitor to measure how strong 4th twitch is to 1st twitch
56
peripheral nerve stimulator (sunmed brand) max output
70mA
1= 7mA
10= 70mA
57
peripheral nerve stimulator (sunmed brand) tetanus Hz max
100Hz
| or 50Hz; if you open battery theres a switch
58
standby button
no pulse generated
59
How does the StimPod Quantitative stimulator work?
measures the strength of each contraction and displays it on the monitor
more accurate than qualitative
60
What are the two types of electrodes?
surface electrodes
| needle electrodes
61
surface electrodes
EKG gel electrodes (may need to remove excess hair and alcojhol swab)
initial threshold is <15mA
62
needle electrodes
useful for conditions when unable to deliver supramaximal stimulus (obese pts)
63
which electrode is negatively charged?
black
depolarizing membrane
should be placed in closest proximity to the nerve
64
When is the charge required to deliver a supramaximal stimulus less?
when the negative electrode is placed distally
65
which lead should be closest to the heart (proximal)?
red
| hyperpolarizing lead
66
how far apart should the leads be placed?
3-6cm
67
subthreshold stimulus
no motor units respond
68
threshold stimulus
one motor unit respondes
| initial threshold stimulation (ITS)
69
submaximal stimuli
increasing number of motor units respond
70
maximal stimulus
all motor units respond
| "pre-relaxant control response"
71
supramaximal stimuli
all motor units respond
72
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
73
How to determine supramaximal stimulus?
use single twitch stimulation every 1-10 sec and increase current until max twitch observed
74
current required to stimulate fibers maximally
at least 40mA
| could be 80mA for obese pt
75
What should the anesthetist do in order to ensure supramaximal current is delivered?
10-20% higher than the maximal stimulus
76
direct muscle stimulation
twitches would be seen but the pt could still be paralyzed
77
two problems with direct muscle stimulation
giving more paralytic when the pt is already paralyzed
| reversing when the pt isnt ready
78
Why is direct muscle stimulation unlikely with our stimulators?
pulse duration is 200microseconds
| max current output is 60-80mA
79
what are the three things that single twitch stimulation is used for?
muscle relaxant onset
supramaximal stimulus
PTC
80
single twitch stimulation with muscle relaxant onset order:
stimulate once every 1-10 secs before relaxant
relaxant given
twitch strength begins to fade
81
3 disadvantages to single twitch stimulation
no fade during recovery
cant distinguish between depol and nondepol
limited use in assessing recovery of block
82
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
83
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
84
TOF definition
4 stimulations over 2 second period
85
When are patients considered "reversible" with neostigmine?
display at least 1 out of four possible muscle twitches
86
how many twitches are RECOMMENDED prior to neostigmine reversal?
2-3 twitches
87
0/4 twitches how many receptors are blocked?
>90%
88
1/4 twitches how many receptors are blocked?
90%
89
2/4 twitches how many receptors are blocked?
80%
90
3/4 twitches how many receptors are blocked?
75%
91
4/4 twitches how many receptors are blocked?
<75%
92
train of four ratio definition
the strength of the first twitch compared to the strength of the first twitch
expressed as %
93
if the T4:T1 ratio is higher what does that mean?
the pt has stronger muscle function
94
What TOF ratio should be achieved before extubation
0.9
| some say 0.7
95
at what TOF ratio does the pt have a residual neuromuscular blockade?
<0.9
96
What has to be used in order to obtain a TOF ratio?
quantitive nerve stimulator
97
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
98
how long do you have to wait between TOF stimulations?
10-30 seconds
99
Which stimulation is good at testing deeper levels of blockade? Why?
tetanus
| stimulates nerve at higher frequency and releases more Ach
100
2 values of tetanus
assess deeper levels of blockade
| sustained tetanus >5sec withour fade for adequate reversal
101
a pt is profoundly paralyzed because no response to TOF or tetanus, how long until TOF twitch
will be awhile before generate TOF twitch
102
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
103
can tetanus differentiate between depolarizers and non depolarizers?
yes, fade is present in nondep
104
what is special about fade with 100Hz tetanus
fade may occur in absence of muscle relaxant from muscular fatigue
105
what is special about 50Hz tetanus
fade only occurs if partial neuromuscular block
| degree of fade similar to TOF
106
PTC
may be able to be elicited even when there is no response to TOF or tetanus
107
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
108
PTC: twitch before tetanus vs twitch after tetanus explain difference
twitch before: smaller contraction, less Ach
| twitch after: larger contraction, more Ach
109
what can assess deeper levels of blockade than tetanus?
PTC
110
With PTC what predicts the time of recovery?
the number of visible twitches
lower #: longer time to wait
higher #: less time to wait
111
for intermediate duration drugs what is the time from a PTC of 1 to reappearance of twitch?
15-20 min
112
A what PTC twitch count should reversal with neostigmine be possible?
10 or greater
113
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
114
What are the two advantages of DBS?
better indicator of fade than tetanus or TOF
| less painful than tetanus
115
effect of the nerve stimulation on the NMJ
if nerve is stimulated faster than 1Hz the NMJ becomes temporarily flooded with Ach
116
what is the one stimulation that can't flood the NMJ with Ach?
single twitch the freqency is 0.1-1Hz (too low)
117
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)
```
118
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
119
how often can DBS be repeated w/o flood of NMJ?
must wait 12-15 seconds
120
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
```
121
how often can tetanus be repeated w/o flood of NMJ?
at least 2 minutes
122
how often can PTC be repeated w/o flood of NMJ?
at least 6 minutes
123
list recovery of muscles soonest to latest
| HIGHLY TESTABLE
```
SOON
diaphragm
rectus abdominus
laryngeal adductors
orbicularis oculi (facial stimulation)
adductor pollicis (ulnar stimulation)
LATEST
```
124
what is the most useful site for determining the onset time for intubation
orbicularis oculi
| because approximates the laryngeal adductors
125
what is the most useful site for confidence that breathing muscles have recovered?
adductor pollicis, ulnar nerve stimulus
126
what site is more likely to have direct muscle stimulation?
facial nerve stimulation
127
what is special about the median nerve?
P6 acupuncture point
| reduces PONV
128
median nerve and PONV prophylaxis?
deliver 50mA current over median nerve single twitch stimulation 1Hz throughout
129
what is an alternative site to facial and ulnar stimulation?
posterior tibial nerve
130
When can reversal with neostigmine be given?
display at least 1/4 twitches
| 2-3 twitches recommended
131
neostigmine dose 4 twitches without fade
0-1mg
132
neostigmine dose 4 twitches with fade
1-2mg
133
neostigmine dose 2-3 twitches
2-3 mg
134
neostigmine dose 1-2 twitches
4-5mg
135
sugammadex reversal dose 4/4 with or without fade and NDMR within prev 3 hr
1mg/kg
136
sugammadex reversal dose 2/4 or 3/4 twitches
2mg/kg
137
sugammadex reversal dose 1/4 twitches
3mg/kg
138
sugammadex reversal dose 0/4 twitches and 1 PTC
4mg/kg
139
sugammadex reversal dose 0/4 twitches and no PTC
wait unless emergency
140
sugammadex immediate reversal dose of RSI roc dose (1-1.2 mg/kg) 3 mins after administration
16mg/kg
141
If neuromuscular blockade is required before the recommended wait time has elapsed (from using sugammadex) what should be used?
nonsteriodal (cisatracurium)
142
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
143
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
144
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
145
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
```
146
Negative inspiratory force (NIF) definition and normal value
greatest negative pressure a pt can generate during inspiration
-50--100 cm/H2O
147
what is NIF measured with?
manometer
| connected to ETT
148
what NIF is adequate for reversal of NM blockade?
-30cmH2O or more
149
what is the most reliable indictor of adequate reversal?
TOF ratio
150
TOF ratio >0.75 indicates what type of reversal?
sustained tetanus 5 sec
head lift 5 sec
NIF -25cmH2O
151
TOF ratio >0.9 indicates what type of reversal?
sit up unassisted and normal pharyngeal function
152
TOF ratio <0.9 indicates what type of reversal?
phayngeal disfunction with risk of aspiration should receive neostigmine
153
physiological factors that prolong duration of MR (6)
```
hepatic and renal disease
hypothermia
increased age
premature neonates
acidosis
Myasthenia gravis
```
154
electrolyte abnormalities that prolong duration of MR (4)
hypocalcemia and hypercalcemia
hypomag and hypermag
hypokalemia
hypernatremia
155
medications that prolong the duration of MR (4)
antibiotics
antiarrhythmics
inhalation agents
prior administration of sux prolongs nondep
156
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
157
can you distinguish with TOF between a nondep and dep phase II?
no
158
when is it possible to get a phase II block?
larger than normal sux dose
| infusion of sux or dosed repeatedly
159
mechanism of phase II dep block
unknown, possible that postjunctional membrane repolarize and there desensitized to Ach
160
when is tachyphylaxis seen with neuromuscular blocks?
phase II depolarizing blockade
161
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)
162
advantages awake extubation (2)
less likely for airway obstruction or laryngospasm
| airway protected
163
disadvantages of awake extubation (2)
coughing and bronchospasm more likely
| turn over time prolonged if wake up slow
164
awake extubation criteria (3)
breathing spontaneously
strong enough to breathe adequately (adequate reversal)
awake enough to protect airway and avoid laryngospasm
165
deep extubation definition
extubates when the patient is breathing spontaneously but ~1MAC
166
advantages of deep extubation
less likely to cough or bronchospasm
| dont have to wait for pt to wake up turnover is faster
167
when is deep extubation preferred?
hernia surgery
nasal septoplasty
tonsillectomy
168
disadvantage to deep extubation (3)
airway not protected
airway will obstruct (always need nasal or oral airway)
laryngospasm still possible
169
deep extubation criteria (3)
breathing spontaneously with adequate tidal volumes
must be truly deep
thoroughly suctioned (prevent laryngospasm)
170
how can you test if a patient is truly deep?
no cough with ETT cuff deflation
| absence of reaction with forceful jaw thrust
171
deep extubation absolute contraindication (4)
full stomach
GERD/hiatal hernia
difficult airway/intubation
airway edema
172
deep extubation relative contraindications
obesity
| patients with OSA
173
post extubation hypoxia possibilities (6)
```
apnea
bronchospasm
atelectasis
pulmonary edema
inadequate reversal
hypoventilation/oversedation
```
174
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
175
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)
176
diagnosis of bronchosparm
auscultation (wheezing)
177
treatment of post extubation bronchospasm
breathing treatment
| epi if severe and nonresponsive to breathing treatment
178
diagnosis of atelectasis
auscultation (diminished breath sounds)
| chest xray
179
treatment for atelectasis post extubation
Bi-level positive airway pressure (BiPAP) mask
180
BiPAP definition
continous positive pressure but higher during inspiration to open alveloi
181
when is BiPAP indicated?
OSA and atelectasis
182
What makes BiPAP better than CPAP
reduced air trapping and easier exhalation compared to CPAP
183
What can BiPAP be performed with?
ETT or facemask
184
diagnosis of pulmonary edema
auscultation (crackles)
| chest x ray
185
treatment of pulmonary edema post extubation
diuretics (if cause is fluid overload)
| possible intubation vs pressure support ventilation
