NM Blockers Flashcards
Signs of adequate reversal
Sustained 5 second head lift (indicates ability to adequately ventilate & protect the airway)
Leg raising (as sensitive as head life for neonates and infants)
Hand grip (more sensitive but less useful)
Spontaneous ventilation
Opening the eyes
Protrude the tongue
Coughing (be aware of possible stage 2–> look at pupils!)
Swallowing
Reaching toward endotracheal tube
Detection of residual block is difficult if
The patient is not awake and cooperative.
Remember that the PNS is just a tool, not the definitive answer on how reversed the patient is! Can still have 4 twitches with 75% of receptors blocked.
These factors can influence how quickly someone recovers for a NM block
- Degree of paralysis;
- pharmakokinetics/dynamics;
- blood levels of relaxant;
- infusion vs. bolus;
- specific antagonist used & dose;
- underlying NM dysfunction;
- drug interactions (enflurane> isoflurane> halothane);
- organ dysfunction;
- acid-base disturbances;
- age
When should we use a PNS?
ALWAYS ALWAYS ALWAYS when a NMB is used***
Also:
- When pharmacokinetics of relaxant are abnormal (hypothermia).
- In disease states (neuro, renal, hepatic)
- When post-op muscle power needs to be optimal (to monitor muscle strength or need to be able to do deep breathing, etc).
- When a continuous Infusion is used
Reasons to monitor twitches
- Wide inter-patient variability in dose requirements
- Facilitates timing of intubation
- Allows careful titration to effect
- Allows assessment of readiness for reversal
- Allows assessment of adequacy of reversal
- Differentiates type of block
- Facilitates early recognition of pseudocholinesterase deficiency
How many amps is the PNS able to generate?
100mA
How is the frequency of stimuli from the PNS measured?
In Hertz (Hz) = 1cycle/sec The common range used is .1 - 100 Hz
.1 Hz = 1 stimulus/10 sec
10 Hz = 10 stumuli/sec
Nerves used for the PNS and their provoked response
Ulnar nerve- elicits adduction of the adductor pollicis
Facial nerve- elicits obicularis oculi
Can also stimulate the median, posterior tibial, and the common peroneal
When might you monitor the facial nerve?
If both arms are tucked to the side
Monitoring this nerve is the most popular and most reliable
Ulnar nerve
Electrode placement for the ulnar nerve
1cm proximal to the crease of the wrist and then another electrode 2-5cm proximal to that one.
You can get a more pronounced response by placing the negative electrode as the most distal one, but either way will work.
Do all muscle groups respond the same way to NMBs?
No. Different muscle groups have different responses to NMBs. THEREFORE, results from one muscle group cannot be extrapolated to other muscles.
It is appropriate to choose a site for monitoring that has a similar response to the muscle of interest**
List of muscles and their sensitivity to NMBs. List from least to most sensitive
Vocal cords (least sensitive / most resistant) Diaphragm Obicularis oculi (facial nerve) Abdominal rectus Adductor pollicis (ulnar nerve) Masseter Pharyngeal EOMs
Which muscle response better reflects the extent of NM blockade of the diaphragm? Obicularis oculi or the adductor pollicis?
Obicularis oculi. It’s sensitivity to NMBs is more similar to the diaphragm’s.
The median nerve, posterior tibial, and common peroneal all have similar response profiles to PNS of this nerve
Ulnar
We can’t use PNS to directly monitor blockade of the diaphragm. So what clues can we use instead?
EtCO2 tracing, bellows, and looking directly at the diaphragm in the surgical field.
Advantage and disadvantage of monitoring the adductor pollicis
Disadvantage: you may still have diaphragm movement even after loss of single twitch or TOF
Advantage: On return of TOF, you should have full diaphragm function (no residual blockade in the diaphragm)
Purpose of single twitch stimulation and setting used
To determine baseline strength PRIOR to administration of NMB. Pattern will be the same whether using depol or non-depol.
Set at 0.1 Hz (1 stimulus every 10 sec)
The twitch response of the adductor pollicis is more likely to represent the degree of blockade at the cords when this med is used
Sux
If using single twitch, does return of full baseline heigh indicate full recovery from NMB?
Not necessarily! Remember that you can’t assess fade with single twitch. Pt may not be fully reversed
What is a phase II block for sux?
Phase II block looks just like a non-depolarizer, but there is no reversal agent for it.
On continuous mode, TOF is repeated every
10th - 12th second
TOF should not be repeated more frequently than every ___seconds
12
Can TOF determine degree of block without having a control value?
Yes! This is one of the advantages of it. Remember that we look at height, but we’re also looking at the TOF RATIO**
Is the TOF ratio subjective or objective?
Subjective
Hz setting for TOF
2Hz
Hz setting for tetanic stimulation
50-200 Hz for 5 seconds
Tetanic stimulation maintains a muscle response in these situations
Normal NM transmission (no blocker on board) and with sux
Normal tetanic response is NOT maintained under these circumstances
NDMR block and Phase II block with sux.
TOF returns to normal ____ min after tetanic timulation
15
Electrode color and sign
Black = ( - ) Red = ( + ) --> red goes closest to the heart
Process of checking tetany
5sec at 50Hz, followed by a single twitch 3 seconds later. This is a very good monitor of how intense a deep block is. Do not do more often than every 6 minutes. TOF will return to normal 15 min after tetany testing.
Can single twitch distinguish between depolarizers and non-depolarizers?
No.
What is double burst stimulation?
Two train of 3 stimuli at 50Hz, separated by 750ms. This makes it easier to detect fade than in low TOF ratios.
TOF ratios less than .3 can be hard to detect.
Three phases of TOF seen after giving a NDMR
1) Intense block phase
- Occurs within 3-6 min of injection
- Called the “period of no response” (because this is an intense block and has no TOF response)
- Length of this phase depends on the agent given, dose given, and sensitivity of the pt
2) Moderate (surgical) block phase
- Begins when the first response to TOF occurs
- This phase is characterized by gradual return of TOF
- Response to TOF correlates to the # of receptors blocked
3) Recovery phase
- Begins once 4 twitches are present
- Now looking at the ratio to determine how recovered they are
What happens if reversal is attempted before return of any twitches?
Partial reversal
Number of twitches needed to reverse?
Minimum of 1, but 2 or 3 is preferable.
Can generally lift head at TOF ratio of
.6
When is double burst stimulation most useful?
After reversal
At TOF ratio of .6, patients can generally do this
Life head for 3 seconds, open eyes, and stick out tongue
At TOF ratio of .75, patients can generally do this
Lift head for 5 seconds, and have WEAK grip strength
At TOF ratio of .8, patients generally
have normal vital capacity and inspiratory force
What is phase II blockade?
Abnormal response to a a depolarizing agent (sux) in a genetically abnormal individual.
Will manifest with fade (abnormal for sux) and prolonged blockade.
Phases for depolarizing blockade
Phase I Block
- Normal response to depolarizing NMB
- No fade to TOF or tetanic stimulation
- No post-tetanic potentiation
Phase II Block
- Occurs in patients with plasma cholinesterase deficiency
- Can also be seen in NORMAL patients after infusion of sux
- Is characterized by fade to TOF and tetanic stimulation, and will show post-tetanic potentiation
In 50% of the population, a phase II block will resolve spontaneously within ____min, however, they should be allowed to recover from the block for up to ______ min
10-15 min
20-25 min
On induction, either of these settings can be used to check twitches
TOF or single twitch at 0.1Hz
If muscle relaxant is needed during the length of the case, they are usually kept at this twitch level
Between 1-2 twitches
If plasma cholinesterases are normal, twitches should return within ___-___ min following sux
4-8 min
In renal failure, the toxic metabolite laudanosine may accumulate with use of this NDMR
Atracurium
Cisatracurium is the drug of choice in the following circumstances
1) Hemodynamically significant changes in HR (>20%) while paralyzed with pancuronium or MAP > 110
2) Concurrent corticosteroid administration
3) Significant renal or hepatic dysfunction
4) History of asthma or bronchospasm (no histamine release)
When does a Phase II Blockade occur?
1) Infusion of sux
2) Atypical acetylcholinesterase
In 50% of the population, reversal of phase II blockade will occur spontaneously within __-__ minutes
10-15
But, the patient should be allowed to recover from the block for up to 20-25 minutes
If sux is given and the person has normal acetylcholinesterase, twitches should return within __-__ minutes
4-8
