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
