NMB Monitoring Flashcards
How can the skeletal muscle be made to relax?
Interfering with transmission along the nerve trunk blocks signals from reaching the terminal bouton (local anesthetics)
Presynaptic - Interfering with Ach production, storage or release (hemicholinium, botulinus toxin, pentamethonium, NMBAs)
Synaptic Cleft – Inactivate neurotransmitter
Postsynaptic – Interfere with depolarization or activation of the end-plate (NMBAs)
What techniques do we use to record/monitor muscle function?
Observation (qualitative), visual, tactile
Mechanomyography (MMG, force displacement)
Electromyography (EMG)
Acceleromyography (AMG)
Kinemyography (KMG)
How many alpha subunits are located on an adult nicotinic receptor to convert the channel to an open state?
2
The fetal nicotinic receptors, following major stress, is characterized by a single subunit substitution. These receptors are characterized by a 10-fold increase in ionic activity, rapid metabolic turnover, and extrajunctional proliferation, thus what must be be cautious of doing?
giving Sux to these pts due to hyperkalemia
Pulse duration must be less than ____ msec so as not to induce repetitive neural firing or direct muscle stimulation.
0.5
What is supramaximal current?
10-20% above the current needed to stimulate all nerve fibers in the bundle
Note: This is readily achieved with needle electrodes less than 10mA.
Stimulation of all nerve fibers within a bundle is easily done with ____ electrodes, but ______ electrodes may fail to stimulate all fibers when they are not in close proximity to the nerve or when the pts are obese.
needle
surface
Needle electrodes require lower stimulation because they bypass impedance of the skin.
What is the low output level of needle stimulators?
What is the risk associated with high current density?
0-40mA
Hazard for electrical burns
Why is the distance b/n electrodes important?
Determines the penetration of depth of the stimulation current
How far should the electrodes be apart from one another?
1 inch
One source says 3-6 cm, other says 2.5-4cm.
What method of monitoring uses a force transducer similar to a BP transducer used to measure the force produced or the distance moved?
mechanical transduction (MMG)
What method uses electrodes, monitor the electrical activity induced in muscle by contraction – similar to ECG?
Electromyography (EMG)
What method of monitoring muscle function measures the acceleration of the muscle body or the attachment of the muscle?
Acceleromyography (AMG)
What method of monitoring muscle function uses motion that is converted to electricity?
Kinemyography (KMG)
What method does this depict?
Mechanical MG (MMG)
What method does this depict?
What is encircled?
EMG
detection electrode
What muscles are stimulated with ulnar nerve stimulation?
adductor pollicis
flexor pollicis brevis
Label
What type of neuromuscular blockade produces this response?
Non-depolarizing or Phase II block
What type of neuromuscular blockade produces this response?
depolarizing
What anatomical positions are suitable for monitoring?
Ulnar Nerve innervating Adductor pollicis and Flexor Pollicis Brevis
Facial Nerve innervating Frontalis and Orbicularis Oculi
Posterior Tibial innervating Flexor Hallucis Brevis
What 2 things should you not do during anode/cathode placement?
Do not place anode (red) between the cathode (black) and the muscle bed being observed.
Do not place the electrodes directly over muscle
Anodal current threshold is approx. ____% more than cathodal.
25
What movement is expected with ulnar nerve stimulation?
thumb adduction, 5th digit movement
What movement is expected with posterior tibial nerve stimulation?
Plantar flexion of the big toe
What movement is expected with peroneal nerve stimulation?
Foot dorsiflexion
What movement is expected with facial nerve stimulation?
orbicularis oculi contraction
What movement is expected with mandibular nerve (V3) stimulation?
jaw closure
A maximal dose of rocuronium has a faster onset time than a submaximal dose.
However, what can we say about the maximal effect with respect to time with a maximal and submax dose?
Both maximal and submaximal doses have a maximal effect at 4 minutes.
Onset for neuromuscular blockade is faster for _____ potent drugs. Name the 2 common ones.
less
Sux, Roc
Note: More potent Vec and Cis take longer.
When the adductor pollicis is maximumally blocked 98% +/- 1, how much are the laryngeal adductors blocked?
77% +/-5
Label the recovery from NMB curves:
Should nerve stimulation be monophasic or biphasic?
monophasic
The evoked tension of the muscle varies with the stimulating current and forms a ________ curve.
sigmoidal
Note: As current increases, the number of nerves reaching threshold increases until all are responding. After all nerves have reached threshold, further increases in current fail to increase motor response.
What initial threshold in mA is needed for stimulation?
What is the mA needed for supramaximal stimulus?
15 mA
32 mA
Stimulation at 10mA will produce same fade response at 60mA. True or false?
True
Takeaway: We want to use the min. current to assess required stimulation.
If you have a depolarizing block and initiate a post-tetanic stimulation, what response do you expect?
None
If you have a non-depolarizing block, and initiate a post-tetanic stimulus, what response do you expect?
A stronger response than initial response
What type of response is depicted?
Post-tetanic non-depolarizing block
What type of response is depicted?
Post-tetanic depolarizing block
Note: The amplitude does not change after post-tetanic stimulus.
What should the current output for a nerve stimulator be adjustable to?
from 10 - 80 mA
As pulse duration becomes greater than ____ msec, muscle stimulation becomes more likely.
0.2 msec
What % receptors are blocked for 4 TOFc, sustained tetany at 50Hz?
70%
What % of receptors are blocked for 4 TOFc, onset of fade at 100Hz?
50%
Note: Measuring at 100Hz rather than 50Hz provides a 20% margin of safety when determining extent of NMB.
There is no discernible decrease in the amplitude of the evoked neuromuscular response until at least _____% of receptors are blocked.
70
How many post-tetanic twitches = 1 TOFc?
10
When reversing the pt with no twitches, what chance of reversal do we have with a post-tetanic count of:
0
5-10
>10 count
0: little chance of reversal
5 – 10 count: possible reversal
>10 count: reversal very likely
The higher the count the more likely the reversal.
If the TOF ratio = 0.7 - 0.75, what would be the correlating signs and symptoms?
- Diplopia
- Decreased grip strength
- Inability to maintain apposition of the incisor teeth
- Tongue depressor test negative
- Inability to sit up without help
- Severe facial weakness
- Speaking is difficult
- Overall weakness/tiredness
What are unreliable tests for post-op neuromuscular recovery? (6)
- Sustained eye opening
- Protrusion of the tongue
- Arm lift to the opposite shoulder
- Normal tidal volume
- Normal or early normal vital capacity
- Max. inspiratory pressure less than 40-50 cmH2O
What are the most reliable test of post-op neuromuscular recovery? (4)
- Sustained head lift for 5 sec
- Sustained leg lift for 5 sec
- Sustained handgrip “ “
- Max inspiratory pressure 40-50 cm H2O or greater
If a pt is able to sustain a 5 sec head lift, what is the approximate TOF ratio?
0.6-0.7
What are conditions associated with upregulation of ACh receptors? (7)
- Spinal cord injury
- Stroke
- Burns
- Prolonged immobility
- Prolonged exposure to NMB
- MS
- Guillain-Barre syndrome
What kind of response do you expect for those that have upregulated ACh receptors to nondepolarizing relaxants?
resistance to nondepolarizers
sensitivity to depolarizers
What situations are associated with downregulation of ACh receptors?
myasthenia gravis
organophosphate poisoning
anticholinesterase poisoning
What type of response do you expect with those that have downregulated ACh receptors?
very sensitive to NMDB
Blocking agents should be avoided.
Note: Chronic elevations of ACh observed with organophosphorus poisoning or chronic use of reversible cholinesterase inhibitors results in down-regulation of AChRs.
What drugs potentiate the action of non-depolarizers?
Antibiotics (aminoglycosides) like gentamicin, tobramycin, amikacin
Lidocaine or other locals
Ca channel blockers
Beta blockers
Diuretics
What inhalational agents produce the most–> least motor blockade?
Least soluble produce greatest blockade
Des>sevo>iso>halo > TIVA
Hyper/hypo-thermia significantly prolongs the onset and duration of NMB.
hypothermia
Stimulation electrodes should not take up a contact area greater than ___-____ mm.
7-11 mm
The fading common after non-depolarizing relaxants is not observed when:
the direct stimulation of the muscle is occurring
additionally weak contractions continue even during deep motor blockade
Reversal of NMB causes what 6 things?
BLUDS (BBLUDS)
Bradycardia
Bronchospasm
Lacrimation
Urination
Defecation
Salivation
What is a neostigmine block?
Too much ACh results in the motor end plate to remain depolarized thus increasing block.
Thus reduce the dose of agent if recovery is almost complete.
