NMBA monitoring Flashcards
Explain neuromuscular transmission
Impulse arrives at motor end plate causing release of ACh from vesicles (Calcium causes exocytosis), ACh diffuses across synapse - binds to receptors on sarcolemma, binding of ACh causes sodium to enter cell and cause depolarization, then sarcolemma repolarizes by potassium leaving and sodium/potassium pump restoring polarity- ACh is broken down by AChE
NMBA action (general)
Prevents ACh to bind to receptors which prevents neurally-mediated muscle membrane depolarization & subsequent muscle contraction
How many ACh-receptors need to be activated to cause depolarization
Only about 20% (which means 80% can be blocked and can’t tell the different in contraction)
Supramaximal stimulus - defined & how much
Stimulating curent to peripheral nerve that is sufficient to cause all NMJ of that nerve to release ACh, in adults usually 30-50 mA
What happens with the nerve stimulus above supramaximal?
Will not get any more muscle contraction
Tetanic stimulation
sustained- whole hand contracts and relaxes after ACh has run out
Post-tetanic count stimulation
50 Hz tetanic stim for 5 sec, wait 3 sec than supramaximal stimulus at 1 Hz - this stimulates more ACh (see twitches when you normally wouldn’t)- if 5-7 responses are detectable after tetanic stimulation - return of TOF response is imminent
Train of Four stimulation defined
4 supramaximal neural stimuli at 2 hertz causing 4 sequential muscular contraction (a little less ACh is released with each stimulus)
How many receptors are blocked with loss of 4th response in TOF?
75-80%
How many receptors are blocked with all 4 twitches in TOF monitoring?
No more than 20%
How many receptors are blocked with loss of 3rd response in TOF?
85%
How many receptors are blocked with loss of 2nd response in TOF?
90%
How many receptors are blocked with loss of 1st response in TOF?
98-100%
What is TOF ratio?
Amplitude of 4th twitch divided by amplitude of 1st twitch. If >70-80%, no more than 20% receptors should be blocked
Double Burst Stimulation
2 sequential bursts of 3 impulses and then 2 impulses at 50 Hz with an interval of 750 msec, a fade of the 2nd impulse compared with first correlates with incomplete NMBA recovery with TOF ratio <0.6
6 measures of muscle response to nerve stimulation
Electromyography (depolarization), mechanomyography (contraction), acceleromyography (contraction), kinemyography (contraction), phonomyography (contraction), & visual/tactile assessments (contraction).
Electromyography - what it is
Based on measurement of muscle compound action potential that occurs with muscle membrane depolarization (electrical*)
EMG amplitude
about 20 mV, does not change with repeated stimulation– give stimulus & stimulus is then measured
What is mechanomyography
Based on isometric measurement of muscle force (no change in length)
How to use mechanomyography
Use ulnar nerve to stimulate adductor pollicus. *Used in research
What is acceleromyography
Based on isotonic measurement of acceleration of thumb (the muscle force is proportional to muscle acceleration - a transducer -piezoelectric- placed over muscle innervated- measures acceleration). *This can only be used on adductor pollicus and hand must be able to move freely, also force changes with repeated stimulation (stair-stepping)
What is kinemyography?
Measurement of thumb movement in response to nerve stimulation
What is phonomygraphy?
Contracting muscle evokes sounds of 4-5 Hz, use microphone over thenar region or first dorsal interosseus muscle in research
Visual/tactile evaluation of TOF ratio
Clinicians not able to detect TOF fade >0.4, only know if paralytic is on or none at all
Visual/tactile evaluation of tetanic fade
Not able to detect fade if TOF ratio >0.4, if fade is present, residual paralysis is likely - if fade is absent, it does not prove paralytic is absent
Non-nerve stimulation techniques for NMBA
Sustained head lift (5 sec) - able to be complete with partial paralytic (if patient cannot sustain head lift, residual paralysis is likely, but if they can it does not mean paralysis is absent). Tongue depressor - if patient cannot keep between teeth residual paralysis is likely, if can does not prove paralysis is absent
Ulnar nerve innervation
Stimulation of ulnar does not produce movement of only the thumb but also every other finger- easy to underestimate neuromuscular blockade because adductor pollicus is most sensitive DO NOT FOLLOW OTHER HAND MUSCLES - WILL GIVE TOO MUCH
Corrugator supercilii monitoring NMBA
Patches at lateral eyebrow, will see motion on medial half of superciliary arch– more resistant to muscle relaxants
Orbicularis oris monitoring NMBA
Place electrodes lateral to the orbit - motion will be on lateral half of upper eyelid- more like adductor policus
What should your TOF ratio be to determine paralytic is effectively worn off?
0.9 - less than that are associated with functional impairment of muscles of pharynx and upper esophagus= aspiration, can also have critical respiratory events. Should be at least 0.8!
NMBA reversal efficacy
Neostigmine is limited- with high levels of paralytic 100% inhibition of acetylcholinesterase may still not be sufficient to compete with paralytic from acetycholine receptor.
Max acetylcholinesterase inhibition neostigmine dose
50-70 mcg/kg
How long will it take for neostigmine to work if only 1 detectable response from TOF
20 minutes to restore TOF to 0.8
How long will it take for neostigmine to work if 2 detectable responses from TOF
15 minutes
When can prompt (<10 minutes) reversal of paralytics occur?
4 responses to TOF
