13. PNS Flashcards
nerve stimulators cause what to be released
Ach from the presynaptic nerve
what prevents Ach stockpile depletion
prejunctional Ach receptors
when will a muscle be unable to contract?
when 100% of the receptors are blocked
muscle relaxants ant Ach _________ bind __________ receptors
muscle relaxants and Ach competitively bind postjunctional receptros
what drug is better at reversing deeper levels of muscle relaxation?
sugammadex
what could happen if we were able to directly stimulate the muscle?
would cause an underestimation of how paralyzed a pt is
factors that cause direct muscle stimulation
> 80 mA current
pulse duration >500micro sec
electrodes on muscle instead of nerve
what is the pulse duration on nerve stimulatiors?
200 micro secs
what is the max current on nerve stimulators?
60-80mA
which nerve is it more common to incorrectly place electrodes?
facial nerve
5 types of nerve stim
single twitch
TOF
tetanus
post tetanic count
double burst stimulation
how are nerve stimulation patterns defined?
by the frequency in which they stimulate the motor nerve
single twitch
1 Hz (1/second)
or
0.1 Hz (1/10 seconds)
TOF
2 Hz
4 stimuli over 2 seconds
how long is each TOF stimuli?
0.2msec
how long is between each TOF stimuli?
500msec
tetanus
continuous nerve stimulation at 50-100Hz
flood NMJ w/max Ach resulting in sustained contraction
Post Tetanic Count
50Hz tetanus
5 seconds
3 second pause
single twitch at 1 Hz
Double Burst Stimulation
3 impulses at 50Hz
750 msec pause
either 2 impulses at 50Hz
or
3 impulses at 50 Hz
DBS 3,3
3 bursts at 50 Hz
750 msec pause
3 at 50 Hz
DBS 3,2
3 bursts at 50 Hz
750msec pause
2 bursts at 50 Hz
nerve stimulation frequency ranking
SLOWEST
Single Twitch
TOF
Tetanus
FASTEST
how long does each pulse duration (twitch) last?
0.2 msec
or
200 microsec
faster nerve stimulation frequencies ==
more Ach into NMJ
fade
something is causing less and less Ach to be released from the presynaptic nerve with each subsequent twitch
absence of fade
equal amount of Ach is released from presynaptic nerve on all twitches
fade requirements
partial neuromuscular block
must be non-depolarizing
faster nerve stim pattern
fade: Zero neuromuscular block
no fade
all twitches strong
fade: Total neuromuscular block
no fade
no twitches
what do nondepolarizers block?
presynaptic
and
postsynaptic
what do depolarizers block?
postsynaptic only
nondepolarizing block
less Ach released
fade observed
depolarizing block
equal Ach released
no fade released
overall twitch height decreased
what nerve patterns can show fade?
TOF
Tetanus
DBS
PTC
what nerve pattern cannot show fade?
single twitch
what frequency do you need to show fade?
> =2Hz
what does fade tell you?
how paralyzed the pt is
no fade means
pt is completely reversed
presence of fade means
pt is partially paralyzed
what is the gold std in assessment of recovery of neuromuscular blockade?
fade
is fade referring to onset or recovery or both?
recovery only
what nerve stim pattern can differentiate between depolarizing and nondepolarizing block?
TOF
Tetanus
PTC
DBS
what nerve stim pattern cannot differential between depolarizing and nondepolarizing?
single twitch
traditional nerve stimulators provide _______ data
qualitative
qualitative nerve stimulator
Max Output
Tetanus
max output: 70mA
tetanus: 100Hz
black electrode
negatively charged
depolarizes membrane
red electrode
positively charged
hyperpolarizes membrane
ulnar nerve electrode placement
red: proximal
black: distal
3-6cm apart
facial nerve electrode placement
red: forehead
black: zygomatic arch in front of ear
subthreshold stimulus
no motor units respondt
threshold stimulus
one motor unit responds
AKA initial threshold for stimulation (ITS)
submaximal stimuli
increasing number of motor units respond
maximal stimulus
all motor units respond
AKA pre-relaxant control response
supramaximal stimuli
all motor units respond
if you dont use enough current to stimulate the nerve….
you can produce a lower strength muscle contraction
weak twitches
what stimulus do we need to stimulate the nerve for maximum twitch height
supramaximal
what current usually stimulates maximum twitches?
40-60mA
single twitch stimulation indications
- muscle relaxant onset
- determine supramaximal stimulus current
- post tetanic count
- continuous nerve stim to decr PONV
can single twitch assess recovery of muscle paralysis?
NOPE
single twich disadvantage
does not produce fade during recovery
cannot assess NMB recovery
cannot destinguish depolarizing vs nondepolarizing
what will happen if you use single twitch to monitor muscle relaxant onset
twitches will gradually fade away
what percentage of receptors must be blocked for twitches to start to fade away when monitoring with single twitch?
75%
where do you place the PNS for PONV stimulation?
ulnar nerve (61% pts had PONV)
median nerve (45% pts had PONV)
use median nerve
what accupuncture site is located on the median nerve?
P6
what current should you stimulate for PONV
50mA on the median nerve through single twitch
what are you comparing if you use single twitch to assess recovery?
max twitch height at end of case == max twitch height prior to muscle relaxant
TOF can tell us
how profound the neuromuscular block is
0 twitches
> 90% block
1 twitch
90% block
2 twitches
80% block
3 twitches
75% block
4 twitches
<75% block
TOF ratio
strength of the 4th twitch compared to the first twitch
higher TOF ratio
lower fade
stronger muscle function
what TOF ratio is indicative of residual neuromuscular blockade?
<0.9
TOF disadvantage
not as good at measuring “deep” levels of blockade
tetanus advantage
assesses deeper levels of blockade
sustained tetanus >5seconds indicates…
that the pts muscle paralysis has been adequately reversed
disadvantage of tetanus
pain
PTC
assesses deepest level of paralysis
lower number of Post tetanic twitches
longer wait for twitch return
15-20 mins
higher number of post tetanic twitches
shorter wait for twitch return
when can you reverse with neostigmine
PTC of 10+
or 2-3 muscle twitches
tetanus increases
total Ach in the synapse
larger contraction
double burst stimulation advantage
easier to see fade with naked eye
why do you wait between re-stimulating a nerve?
if you dont wait, it will produce a stronger muscle contraction
so you will underestimate the neuromuscular block
what pattern do you use for supramaximal stimulus?
single twitch
what pattern is good at assessing muscle relaxant onset?
sing twitch
what pattern is good at assessing partial blockade and recovery from blockade?
TOF
tetanus
PTC
DBS
what pattern differentiates between depolarizing and nondepolarizing?
TOF
tetanus
PTC
DBS
what patter can assess deep levels of blockade?
tetanus
PTC
DBS
time between TOF stimulations
10-30s
time between DBS stimulations
12-15s
time between tetanic stimulations
2 mins
time between PTC stimulations
6 mins
recovery of muscles order
- diaphragm
- rectus abdominus
- laryngeal adductors
- orbicularis oculi
- adductor pollicis
which nerve site is the best for determining onset time for intubation?
facial nerve
(orbicularis oculi)
facial nerve approximates
laryngeal adductors
which nerve site gives best confidence that breathing muscles are recovered?
ulnar nerve
direct muscle stimulation is most likely on what nerve
facial nerve
alternate nerve monitoring site
posterior tibial nerve
neostigmine dosing: 4 twitches w/o fade
0-1 mg neostigmine
neostigmine dosing: 4 twitches w/fade
1-2 mg neostigmine
neostigmine dosing: 2-3 tiwtches
2-3 mg neostigmine
neostigmine dosing: 1-2 twitches
4-5 mg neostigmine
sugammadex dosing: 4/4 w or w/o fade
1mg/kg
sugammadex dosing: 2/4 or 3/4
2 mg/kg
sugammadex dosing: 1/4
3 mg/kg
sugammadex dosing: 0/4 w/1 twitch post tetanus
4 mg/kg
sugammadex dosing: 0/4 and no post tetanic twitch
wait
what dose of Roc is needed to re-paralyze the pt?
dose of sugammadex: <4mg/kg
>= 4 hrs ago
0.6mg/kg
what dose of Roc is needed to re-paralyze the pt?
sugammadex: 4 mg/kg
<= 5 mins
1.2 mg/kg
when do you have to wait 24 hrs after sugammadex to re-use Roc?
if 16 mg/kg dose was used
renal insufficiency/failure pts
what can you use instead of Roc to re-paralyze the pt?
Cisatracurium (nimbex)
indicators of adequate reversal
sustained head lift (5 sec)
sustained tetanus (>5 sec)
tidal volume (5-10 mL/kg)
strong grip
NIF (-50 to - 100 cmH2O)
TOF ratio
NIF
the greatest negative pressure a pt can generate during inspiration
what NIF means a pt is extubatable?
-20 to -30 cmH2O
what NIF indicates adequate reversal but no airway protection?
-25cmH2O
what NIF indicates adequate reversal w/airway protection?
-30 cmH2O
what is the most reliable indicator of adequate reversal
TOF ratio
TOF ratio >0.75
5 sec head lift
sustained tetanus >5 s
cough
NIF -25 cm/H2O
TOF ratio >0.9
pts can sit up unassisted
normal pharyngeal function
TOF ration <0.9
risk of aspiraiton
Physiologic factors that prolong duration of MR
hepatic disease
renal disease
hypothermia
increased age
MG
premature neonates
acidosis
electrolyte abnormablites that prolong duration of MR
hypocalcemia
hypercalcemia
hypomagnesemia
hypermagnesemia
hypokalemia
hypernatremia
meds that prolong duration of MR
aminoglycoside antibiotics (gentamicin)
inhalational agents
local anesthetics
ca channel blockers (verapamil)
antiarrythmics (diltiazem)
lithium (prolongs sux)
sux (prolongs NDMR)
phase II block
depolarizing block that resembles a nondepolarizing block
causes of phase II block
larger dose of sux (>6mg/kg)
sux redosing or infusion
how do you reverse a phase II block
neostigmine
or waiting
awake extubation advantages
less risk of obstruction
less risk of laryngospasm
protected airway
awake extubation disadvantages
coughing
bronchospasm
slow turn over time
awake extubation criteria
spotaneous ventilation
strong enough to breath
responds to commands
deep extubation
extubates when pt is spontaneously breathing but fairly anesthetized
deep extubation advantages
less likely to cough
faster OR turnover time
what surgeries might you want a deep extubation?
hernia
nasal septoplasty
tonsillectomy
deep extubation disadvantages
airway not protected
airway obstruction
laryngospasm
deep extubation absoluted contraidications
uncontrolled GERD
full stomach
hiatal hernia
difficult airway
airway edema
deep extubation criteria
sponteneously breathing
adequate tidal volumes
truly deep
thoroughly suctioned
deep extubation relative contraindications
obesity
OSA
