Download Neuromuscular junction monitoring

Neuromuscular
junction monitoring
Electrodes
Stimulation is achieved by passing two electrodes along a nerve and passing a current through them
It can be carried out either transcutaneously using surface electrodes or percutaneously wih needle electrodes
TYPES
A- Surface ElectrodesCan be those used for measuring ecg
Electrode skin resistance decreases with large conducting area, as do skin burns and pain
Large conducting area makes it difficult to obtain supramaximal stimulation
Moreover it can stimulate multiple nerves, so it may be better to use pediatric electrodes
Skin should be properly cleaned end rubbed with abrasive
Electodes for peripheral n. stimulation have different thicknessthan ecg electrodes and have chemical buffers to maintainskin surface ph
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METAL ELECTRODES
Two metal plates or balls spaced 1 inch
apart,which attach directly to stimulator
--convenient to use
--no good contact
--burns have been reported with their use
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NEEDLE ELECTRODES
Useful for providing supramaximal stimulus
--useful when skin is thickened,cold,edematous and in
obese,
Also useful in hypothyroid,diabetic and renal failure pts
Other complictions—
Broken needles,infections burns ,nerve damage
There is alo a greater chance of direct muscle
stimulation
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POLARITYStimulators produce direct current by using one
negative and one positive electrodes
Usually positive electrode is red and negative is black
Maximal effect is achieved when negative electrode is
placed just over nerve to be stimulated
Positive electrode should be placed along the course of
the nerve usually proximally to avoid direct muscle
stimulation
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METHODS for evaluating evoked responses
A--VISUALObserver should be at an angle of 90 deg. To the motion
Used to count—
No of responses present in TOFstimulus, determine PTC,detect
presence of fade with TOFor DBS
POST TETANIC FACILITATION CAN ALSO BE
ASSESSED
TOFR is difficult to determine
Visually assessing fade with 100hz tetanic stimulation is fairly
accurate for analyzing residual paralysis
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B--- TACTILE
Accomplished by placing the evaluators fingertips
lightly over ms to be stimulated and feeling the strength
of contraction
More sensitive for assessing NMB using TOF.
It can be used to evaluate the presence or absence of
responses and/or fade with train of four,double
burst,and tetanic stimulation
PTC can be determined
TOFR CAN BE DETERMINED if there is response
to all fourstimuli with TOF
Mechanomyography MMG
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Utilizes force displacement transducer, such as a strain
gauge,attached to fingeror other part of body that can be
restrained by a preload and will move when stimulated
The transducer converts the contrctile force into electrical
signal,which is amplified and displaced on monitor screen or
recorded on chart
Can measure single twitch height,response to tetanic stimulation
and TOFR ACCURATELY
Cumbersome, difficult to setup
For accurate results maintenance of muscle temperature within
limits is required
Gold standard of scientific measurements of NM system
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ACCELEROMYOGRAPHY(ACG,AMG)
Thin piezoelectric transducer is fixed to a moving part.
When the part moves voltage is proportional to
acceleration of the moving part
Method requires unrestricted movement of the muscle
being stimulated
Easy and convenient to use, relative inexpensive and
can be interfaced with computer
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KINEMYOGRAPHY (KMG)
Utilizes bending sensor placed between thumb
and forefinger
Core of sensor is piezoelectric material
Movement is determined by change in the shape
of material when it is bent by adductor pollicis
muscle contraction
KMG has been compared with MMG except for
determining recovery from NMB
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PIEZOELECTRIC FILM
Uses disposable piezoelectric film. This is placed
so that it spans a movable joint and muscle
movement causes the bending of the film which
generates voltage which is proportional to the
amount of bending
Not as accurate as MMG
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ELECTROMYOGRAPHY(EMG)
Process of recording electrical activity of muscle
When motor n is stimulated , a biphasic action potential is
generated in each of the muscle cells it supplies unless some
degree of NMB exists. The sum of these action potentials can
be sensed by using electrodes placed overmuscle being
stimulated
Total 5 electrodes are used
2 stimulating electrodes on the nerve to be stimulated
3electrodes –2 receiving ,and one ground are used for recording
Best results are seen when electrodes have been in contact with
skin for 15 min before calliberation
Carefull skin preparation helps to give good results
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EMG of larynx can also be done
EMG machine automatically determines the
supramaximal stimulus, establishes a control
response stimulates at selected intervals ,
measures response and compares it with control
.
With nondepolarizing NMB , the action
potential amplitude is decreased and there is
fade with TOF
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Advantages of EMG over MMG
A-less immobilization is required
B-hand or arm need not to be extended or put
on board .
C – can be used to monitor laryngeal or
diaphragmatic muscles
D– can be used to assess motor nerve blocks
induced by regional anaesthesia
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Disadvantages—
Sensitive to electrical interference
Response varies according to ms used
Expensive
Response amplitude inc. with dec. temperature
Since site is not immobilized, changes in relative
position of recording electrodes cause variation
in EMG response
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PHONOGRAPHY
Aka acoustic myography
When ms contrcts ,sounds are emitted. These acoustic
waves propagate through skin, generating waves which
can be recorded by small piezoelectric microphone
Easy to use and can be used on no of different muscles.
Provides stable baseline with little disturbances from
artifacts
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MONITORING SITES
1– ULNAR N--Most commonly used and adductor pollicis is most commonly
monitored
Can be stimulated at elbow , wrist or hand
Wrist– thumb adduction and finger flexion
Elbow– hand adduction + above
Wrist—2 electrodes placed along medial aspect of distal
forearm, 2 cm proximal toproximal wrist skin crease with
negative electrode distal
Elbow---over sulcus of medial epicondyle of the humerus
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EMG monitoring of ulnar nerve
Recording electrodes—hypothenar , thenar , dorsal interosseous
ms. For dorsal inter. Ms , active receiving electrode is placed in
the web between the index finger and the thumb and the other
electrode at the base of second finger
Hypothenar eminence--both electrodes are placed on palmar side over or the
active electrode is placed over hypothenar eminence and the
other below the second line on the ring finger or at the base of
the dorsum of 5th finger
MEDIAN NERVE—
 Wrist-place the electrodes medial to where it would
have been for ulnar n
 Elbow- adjacent to brachial art.
 --stimulation causes thumb adduction
TIBIAL NERVE
Popliteal fossa—gastroecnemius ms stimulated—causes
significant leg movements
Sensing electrodes over lateral head of gastroecnemius ms
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POSTERIOR TIBIAL NERVE
Electrodes placed behind the medial malleolus and
anterior to achillis tendon at the ankle
Stimulation causes plantar flexion of the foot and big
toe
Especially useful in children, when it is difficult to find
room on the arms; or when hand is inaccessible
There is a lag time with slower onset of relaxation than
with ulnar n.
PERONEAL NERVE
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electrodes on lateral aspect of of knee
 Stimulation causes dorsiflexion of foot
FACIAL NERVE
Most useful in detecting the onset of relaxation in ms of jaw, larynx ,diaphragm.
ACG can be used with facial nerve
Negative electrode—ant. To inferior part of ear lobe
Positive---just posterior or inferior of the lobe
This configuration is more
specific
corrugated supercilli ms should be observed . With ACG ,the transducer should be placed
in the middle of supercilliary arch
The facial n should not be used to assess recovery fromNMB becoz responses may show
complete recovery while significant NMB is stii present
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RECURRENT LARYNGEAL N
Innervates most of the intrinsic ms of larynx
It can be stimulated percutaneously by using two
electrodes betweenthe notch between the thyroid and
cricoid cartilage
Response can b measured by placing tracheal tube cuff
and measuring pressure changes within cuff
EMG in larynx can also be accomplished
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USES
Before induction----dry ,clean electrodes should be connected to
stimulator and placed over selected nerves
Skin should be thoroughly cleaned
Electrodes should be checked to see if the gel is moist
Piece of tape should be placed over electrodes to
prevent displacement
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INDUCTION
Stimulator can be used to determine-onset time of
NMB, detect unusual sensitivity to relaxants and to
determine whether the pt is sufficiently relaxed for
intubation
Stimulator should be turned on after induction but
before giving ms relaxants
Output of stimulator should be inc. until the response
does not increase with increasing current, then inc. 1020%
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INTUBATION
Onset of NMB will be faster in centrally located ms like diaphragm, facial ,
laryngeal and jaw ms than peripheral ms
Monitoring the response of eye ms will reflect the time of onset and level of
NMB at airway musculature more closely than monitoring peripheral ms
which will underestimate the rate of onset of NMBin airway muscles and may
overestimate the degree of block
In majority of pts dissapearence of adductor pollicis response is ass. With
good intubating conditions
In EMG monitoring hypothenar eminence may be preferable
Single twitchat 0.1hz is used and clinician wait until the response is barely
perceptible before attempting intubation
double burst has been used as an indicator of optimal conditions for tracheal
intubation
MAINTAINENCE
 During maintenance stimulator can be used to titrate relaxant dosage to the
needs of the operative procedure so both over and underdosages are avoided
 It is important to correlate the reaction to nerve stimulation with pts clinical
condition becoz there may discrepancy between degree of relaxation of the
monitored site and that of ms at the site of surgery
 TOF is considered the most important pattern for monitoring NMB during
anaesthesia
 Supramaximal currents are generally used
 GOAL– maintain at least one response to TOF stimulation
--- no response—further administration of relaxants is not indicated
-----2 responses—abd. Relaxation adequate during balanced anaesthesis
---- 3 responses—adequate relaxation if volatile agent is used
one twitch is added to above recommendation if facial ms are used
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RECOVERY AND REVERSAL
Nerve stimulator can detect residual NMB
As recovery progresses TOF responses gradually inc.
It is best to use a peripheral ms to monitor recovery becoz its complete recovery
would indicate residual ms weakness contributing to problems with airway
patency are unlikely
In past TOFR—0.7 WAS CONSIDERED ADEQUATE
Now TOFR-- >90% at adductor pollicis before extubation by MMG
IF EMG monitoring is used, residual anaesthetic effects usually prevent the
return of T1 to preanaesthetic reference levels ,but TOFR should exceed 90%
Residual NMB cannot be reliably detected using TOF if visual/ tactile
monitoring is used
Detection is somewhat better with TOF
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Hazards—
Burns most commonly with needle electrodes
Nerve damage—thumb paraesthesias in MMG
due to intramural placement of needle
electrodes
Comlications with needle electrodes--Pain
Electrical interference