Peripheral Nerve Stimulator Flashcards
how long does each nerve stimulus last?
0.2 msec
when will a twitch or muscle contraction occur?
if receptors aren’t blocked
what plays a role in preventing stockpiles of Ach inside the nerve from being depleted?
prejunctional Ach receptors
what happens when 100% of the receptors are blocked (profound neuromuscular blockade)?
no muscle contraction occurs
which drug works by binding and encapsulating and taking the muscle relaxant out of the neuromuscular junction
sugammadex
what are the 5 types of nerve stimulation patterns?
- single twitch
- train of four
- tetanus
- post tetanic count
- double burst stimulation
2 types of single twitch nerve stimulation
- 1 Hz
2. 0.1 Hz
what is a 0.1 Hz single twitch nerve stimulation?
1 stimulation per 10 seconds
what is a 1.0 Hz single twitch nerve stimulation?
1 stimulation per second
how many stimuli does TOF deliver and over how long?
4 stimuli (0.2 sec each) over 2 second period (2 Hz)
most painful nerve stimulation
tetanus
what is the stimulation for tetanus?
50-100 Hz over 5 seconds or less
post tetanic count is a ____ tetanus that is applied for ____ seconds followed by a ____ second pause followed by ________ at 1 Hz.
50 Hz; 5 seconds; 3 second ; single twitch stimulation
two short tetanic stimulations separated by a 750 msec pause
double burst stimulation (DBS)
What is the FIRST tetanic stimulation in DBS?
3 impulses at 50 Hz
What is the SECOND tetanic stimulation in DBS?
2 options: 1. two impulses at 50 Hz
2. 3 impulses at 50 Hz
DBS 3,3
3 bursts at 50 Hz
750 msec pause
3 more bursts at 50 Hz
DBS 3,2
3 bursts at 50 Hz
750 msec pause
2 more bursts at 50 Hz
which nerve stimulation has the lowest stimulation frequency (1-10Hz) and longest stimulation duration
single twitch
which nerve stimulation has the faster stimulation frequency (2-100 HZ) but shortest stimulation duration?
TOF and tetanus
when a nerve is stimulated multiple times in a row __ can occur if the pt has a partial neuromuscular block
fade
What does seeing fade mean?
something is causing less Ach to be released from the presynaptic nerve with each subsequent twitch
what does it mean whenever we see that all the twitches have the same strength ( no fade) ?
an equal amount of Ach was being released from the presynaptic nerve on ALL the twitches
what do nondepolarizing muscle relaxants block ?
both presynaptic and postsynaptic Ach receptors
how do stockpiles of Ach get back to normal with a partial neuromuscular block?
the nerve needs to be rested for a short period of time without being stimulated
describe the 4 things that happen the greater degree of muscle paralysis
- higher # of prejunctional receptors that will be blocked
- the lower amt of Ach that’ll be released on subsequent back to back stimuli
- the higher the degree of fade
- the longer the nerve will have to “rest” before stockpiles of presynaptic Ach can be restored
what do depolarizing muscle relaxants block?
postsynaptic Ach receptors
when will you not see fade?
during partial depolarizing Phase I block
why is the twitch height decreased in partial depolarizing phase I block?
postjunctional receptors are still blocked
What are the two things needed for fade to occur?
- there must be a partial neuromuscular nondepolarizing block
- the nerve must be stimulated at a relatively high frequency
what is the gold standard for assessment recovery of NM blockade?
fade
when will a pt for sure be adequately recovered from NM blockade?
when the pt’s fourth twitch is as strong as the first twitch (no fade is present)
what happens during ONSET of partial nondepolarizing block?
twitch height gradually decreases w/ TOF and single twitch stimulation
what happens during ONSET of partial depolarizing block ?
twitch height gradually decreases with both TOF and single twitch but you wont see fade with each individual train of four pattern
when do you see fade during recovery of nondepolarizing block?
fade with TOF (NOT single twitch)
which nerve stimulation cannot differentiate between depolarizing and nondepolarizing block?
single twitch stimulation
which nerve stimulation(s) CAN differentiate between depolarizing and nondepolarizing block?
TOF, tetanus, post tetanic count, and double burst stimulation
when can you see twitches with sux?
during neuromuscular onset using single twitch stimulation
information about quantities (information that can be measured with numbers)
quantitative data
information that cannot measured or info about qualities
qualitative data
traditional nerve stimulators are more ____ (qualitative or quantitative)
qualitative
traditional nerve stimulators (SunMed brand) deliver maximum output current of how much?
70 mA
tetanus in a traditional nerve stimulator (SunMed) brand is ___ Hz.
100
the sun med plus brand you can choose between __ or __ Hz tetanus and has a ____ as an option
50 or 100; double burst stimulation
the StimPod is an example of ___
newer quantitative peripheral nerve stimulator
the StimPod can use which of the following nerve stim?
TOF, double burst, and post tetanic count stimulation
where should the negatively charged electrode be placed to achieve a maximal twitch height?
closest proximity to nerve
for the ULNAR nerve, where should the red and black electrodes be placed?
red should be proximal and black should be distal
for the facial nerve where should the negative electrode be placed?
over the temporal branch of facial nerve; red can be placed on forehead (zygomatic arch good landmark)
no motor units respond
subthreshold stimulus
one motor unit responds
threshold stimulus
increasing number of motor units respond
submaximal stimulus
all motor units respond
maximal stimulus
AKA pre-relaxant control response
maximal stimulus
all motor units respond
supramaximal stimuli
what kind of stimulus current should anesthetists use for nerve stimulators?
supramaximal stimulus
how do you determine the supramaximal stimulus current ?
using a SINGLE TWITCH stimulation and performing a single twitch every 1-10 seconds
what is the current required for supramaximal stimulus?
40 mA
what is the current required for supramaximal stimulus for the ulnar nerve for a 60 kg female pt?
30-40 mA
what is the current required for supramaximal stimulus for the ulnar nerve for a very obese or large individual?
80 mA
what current must be applied for supramaximal stimulus to the PERIPHERAL nerve?
50-80 mA
An anesthetist should set the current _____ higher than what they observe the maximal stimulus to be.
10-20%
what are the two problems with direct muscle stimulation?
- dosing more muscle relaxant when the pt is already profoundly paralyzed
- reversing muscle paralysis when the pt isnt ready
why is direct muscle stimulation unlikely? (2)
- the pulse duration on our nerve stimulator is 200usec
2. the max current output on our nerve stimulators is usually 60-80 mA
to ensure the current is supramaximal current while avoiding direct muscle stimulation, what should you turn the nerve stimulator up to?
max current output 70 mA
Indications for single twitch nerve stimulation (3)
- satisfactory conditions for intubation (muscle relaxant onset)
- supramaximal stimulus
- post tetanic count (PTC)
3 steps when using single twitch stimulation to determine muscle relaxant onset?
- anesthetist stimulates the nerve once every 1-10 seconds (0.1-1.0 Hz)
- muscle relaxant is administered
- once muscle relaxant takes effect, the twitch strength begins to gradually fade away (NOT FADE THOUGH)
when does twitch height begin to decrease during a single twitch stimulation to determine muscle relaxant onset?
when 75% of the receptors are blocked
what are the disadvantages to single twitch stimulation (3)?
- fade during recovery is not likely to be observed
- it cannot distinguish b/w depolarizing and nondepolarizing block
- limited use in assessing recovery from NM block
this nerve stimulation pattern is an indication of how profound NM blockade is
TOF
how many muscle twitches should a pt display prior to neostigmine reversal?
at least 2-3 muscle twitches
0 out of 4 twitches
> 90% receptor block
1/4 twitches
90% receptor block
2 twitches
80% receptor block
3 twitches
75% receptor block
4 twitches
<75% receptor block
T4:T1= 60% means..?
4th twitch is 60% as strong as the 1st twitch
T4:T1= 100% means…?
4th twitch is just as strong as the 1st twitch
3 outcomes of having a higher T4:T1 ratio
- stronger the 4th twitch will be compared to the 1st twitch
- lower the fade will be
- the stronger the muscle function
TOF disadvantages (3)
- less useful in assessing partial DEPOLARIZING block
- its not quite as good at measuring deep levels of blockade
- its not as useful in assessing muscle relaxant onset
which nerve stimulation can assess the deepest levels of blockade?
post tetanic count
what is a great indicator that the pt’s muscle paralysis has been adequately reversed?
sustained tetanus for >5 seconds without fade
in post tetanic count, a twitch before tetanus means?
less total Ach in the synapse (smaller contraction)
in post tetanic count, a twitch after tetanus mean>?
more total Ach in the synapse (larger contraction)
what predicts the time of recovery?
number of post tetanic twitches
True/False: the lower the number of post tetanic twitches the longer the anesthetist will have to wait for a return of a single twitch.
TRUE .
what indicates a residual block in DBS?
a decrease in second response; fade is more easily detected with DBS than TOF
advantages of DBS (2)
- better indicator of fade than tetanus or TOF
2. less painful than tetanus
what two factors effect the degree to which the NMJ is flooded with Ach by nerve stimulation patterns?
- stimulation frequency
2. stimulation duration
what will happen if you stimulate a nerve right after the NMJ had been flooded with Ach?
produces stronger muscle contraction; UNDERESTIMATES the NM block making you think the pt is less paralyzed than they really are
how often can DBS be repeated?
12-15 seconds
how often can TOF be repeated?
10-30 seconds
how often can tetanus be repeated?
2 minutes minimum time that should pass before repeating tetanus stimulation
how often can PTC be repeated?
6 minutes
best stimulation pattern for determining muscle relaxant onset
single twitch
which muscle is soonest to recover from paralysis?
diaphragm
which muscle twitches with ulnar nerve stimulation and is LAST to recover from paralysis?
adductor pollicis
which muscle twitches with facial nerve stimulation?
orbicularis oculi
What is the order of recovery of muscles from paralysis? (start with soonest to recover)
- diaphragm
- rectus abdominus
- laryngeal adductors
- orbicularis oculi
- adductor pollicis
the most useful site for determining onset time for intubation
orbicularis oculi; facial nerve stimulation
which muscle recovery provides the most confidence that the breathing muscles have recovered?
adductor pollicis
stimulation at this point reduces PONV
median nerve/ P6 acupuncture point
what is used during PONV prophylaxis? (current and type of nerve stimulation)
50 mA current over the median nerve using single twitch stimulation at 1 Hz.
when can reversal of neostigmine be given?
display at least one of four possible muscle twitches
how does LC dose neostigmine with 4 twitches w/o fade
start with =0-1 mg neostigmine
how does LC dose neostigmine with 4 twitches w/ fade?
start w/ 1-2 mg neostigmine
how does LC dose neostigmine with 2-3 twitches
start with 2-3 mg neostigmine
how does LC dose neostigmine with 1-2 twitches
4-5 mg neostigmine
what is the immediate reversal of RSI dose of Roc 3 mins after administration for sugammadex?
16 mg/kg
what are the 6 indicators for adequate reversal?
- sustained head lift
- sustained tetanus
- tidal volume
- strong hand grip
- negative inspiratory force (NIF)
- TOF ratio
what is a normal inspiratory force?
-50 to -100 cm/H20
what is an adequate NIF for reversal?
-35 to -20
TOF ratio >0.75 is equal to?
sustained tetanus and head lift for 5 seconds, an effective cough and NIG of -25 cm/H20
TOF ratio of >0.9 mean?
patients can sit up unassisted and have normal pharyngeal function
physiologic factors that prolong duration of muscle relaxants (6)
- hepatic and renal disease
- hypothermia
- increased age
- premature neonates
- acidosis
- myasthenia gravis
electrolyte abnormalities that prolong duration of muscle relaxants (4)
- hypocalcemia and hypercalcemia
- hypomagnesemia and hypermagnesemia
- hypokalemia
- hypernatremia
medications that prolong duration of muscle relaxants (4)
- antibiotic
- antiarrhythmic agents
- inhalational agents
- prior administration of sux prolong duration of nondepolarizing drugs
what causes a phase II block? (2)
- larger than normal doses of sux (>6 mg/kg)
2. sux is doses repeatedly or run on an infusion
what are the 3 awake extubation criteria?
- pt must be breathing spontaneously
- pt must be strong enough to breath adequately
- pt must be awake enough to protect their airway and avoid laryngospasm
when is deep extubation ABSOLUTELY CONTRAINDICATED? 4
- full stomach
- GERD/hiatal hernia
- difficult airway/intubation
- airway edema
relative CI for deep extubation
- obesity
2. pts with OSA
extubation criteria for deep extubation? 3
- pt must be breathing spontaneously w/ adequate tidal volumes
- the pt must be truly deep (test by absence of coughing when deflating the cuff or absence of rxn with a foreceful jaw thrust)
- the pt must be thoroughly suctioned
6 possibilities of post extubation hypoxia
- apnea
- bronchospasm
- atelectasis
- pulmonary edema
- inadequate reversal
- hypoventilation/oversedation
tx for post extubation apnea
- jaw lift with mask
- jaw lift with mask and oral airway
- gentle positive pressure with oral airway in place
- LMA vs propofol/Sux
tx for atelectasis
biPAP mask (higher positive pressure at inspiration)
tx for pulmonary edema
- diuretics if the cause fluid overload
2. possible intubation vs. pressure support ventilation
