Download NEUROMUSCULAR MONITORING

NEUROMUSCULAR
MONITORING
Moderator: Dr.Dara Singh Negi
Presented by: Dr. Arun K Sharma
Objectives of NM Monitoring
• Onset of NM Blockade.
• To determine level of muscle
relaxation during surgery.
• Assessing patients recovery from
blockade to minimize risk of residual
paralysis.
Why do we Monitor?
Residual post-op NM Blockade
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Functional impairment of pharyngeal and
upper esophageal muscles
Impaired ability to maintain the airway
Increased risk for post-op pulmonary
complications
Difficult to exclude clinically significant
residual curarization by clinical evaluation
Who should be Monitored ?
• Patients with severe renal, liver disease
• Neuromuscular disorders like myasthenia
gravis, myopathies, UMN and LMN lesions
• Patients with severe pulmonary disease or
marked obesity
• Continuous infusion of NMBs or long acting
NMBs
• Long surgeries or surgeries requiring
elimination of sudden movement
Principles of Peripheral Nerve
Stimulation
• Each muscle fiber to a stimulus follows an allor-none pattern
• Response of the whole muscle depends on the
number of muscle fibers activated
• Response of the muscle decreases in parallel
with the numbers of fibers blocked
• Reduction in response during constant
stimulation reflects degree of NM Blockade
• For this reason stimulus is supramaximal
Essential features of equipment:
• Square-wave impulse,
0.1- 0.5 msec duration.
• Constant current variable voltage
Battery powered.
• Multiple patterns of stimulation
(single twitch,train-of-four, doubleburst, post-tetanic count).
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Key features of exogenous nerve
stimulation:
Nerve stimulator: A battery powered device that delivers depolarizing
current via the electrodes.
Stimulus strength: It is the depolarizing intensity of stimulating current. It
depends on duration (pulse width) of the stimulus and on the current
intensity that reaches the current nerve fibers.
Pulse width: It is the duration of the individual impulse delivered by the
nerve stimulator . The impulse should be <0.5 msec³ and 0.1 msec in
duration to elicit nerve firing at a readily attainable current. Pulse width
>0.5 msec extends beyond the refractory period of the nerve resulting in
repetitive firing. The stimulus should produce mono-phasic and rectangular
waveform.
Current intensity : It is the amperage (mA) of the current delivered by the
nerve stimulator(0-80 mA). The intensity reaching the nerve is determined
by the voltage generated by the stimulator and resistance and impedance of
the electrodes, skin and underlying tissues.
Nerve stimulators are constant current and variable voltage delivery
devices.
Reduction of temperature increases the tissue resistance (increased
impedance) and may cause reduction in the current delivered to fall below
the supramaximal level
• Threshold current : It is the lowest current required to
depolarize the most sensitive fibres in a given nerve bundle
to elicit a detectable muscle response.
• Supramaximal current :
It is approximately10-20% higher intensity than the current
required to depolarize all fibres in a particular nerve bundle.
This is generally attained at current intensity 2-3 times
higher than threshold current.
• Submaximal current : A current intensity that induces
firing of only a fraction fibres in a given nerve bundle. A
potential advantage of submaximal current is that it is less
painful than supramaximal current.
• Stimulus frequency : The rate (Hz) at which each impulse
is repeated in cycles per second (Hz).
Electrodes
• Surface electrodes
• Pregelled silver chloride surface electrodes for
transmission of impulses to the nerves through the
skin
• Transcutaneous impedance reduced by rubbing
• Conducting area should be small(7-11mm)
• Needle electrodes
• Subcutaneous needles deliver impulse near the
nerve
METAL BALL ELECTRODES
 Two metal balls or
plates spaced about 1
inch apart, which
attach directly to the
stimulator
 convenient to use but
no good contact
 Burns
POLARITY
 Stimulators produce a direct current by using
one negative and one positive electrode
 Should be indicated on the stimulator
 Maximal effect is achieved when the negative
electrode is placed directly over the most
superficial part of the nerve being stimulated
 The positive electrode should be placed along
the course of the nerve, usually proximally to
avoid direct muscle stimulation
Electrode placement:
• Ulnar nerve: place
negative electrode
(black) on wrist in
line with the smallest
digit 1-2cm below
skin crease
• positive electrode (red)
2-3cms proximal to the
negative electrode
• • Response: Adductor
pollicis muscle – thumb
adduction
• Facial nerve: place
negative electrode
(black) by ear lobe
and the positive (red)
2cms from the
eyebrow (along facial
nerve inferior and
lateral to eye)
• • Response: Orbicularis
occuli muscle – eyelid
twitching
• Posterior tibial nerve:
place the negative
electrode (black) over
inferolateral aspect of
medial malleolus (palpate
posterior tibial pulse and
place electrode there) and
positive electrode (red) 23cm proximal to the
negative electrode
• • Response: Fexor hallucis
brevis muscle – planter
flexion of big toe
Patterns of Stimulation
• Single-Twitch Stimulation
• Train-of-Four Stimulation
• Tetanic Stimulation
• Post-Tetanic Count Stimulation
• Double-Burst Stimulation
Single-Twitch Stimulation
• Single supramaximal stimuli applied to a nerve
at frequencies from 1.0Hz-0.1Hz
• Height of response depends on the number of
unblocked junctions
• Prerelaxant control value is needed
• Does not detect receptor block of <70%
• Used to assess potency of drugs
• Stimulation dependent onset time
Single-Twitch Stimulation
Train-of-Four Stimulation
• Four supramaximal stimuli are given every 0.5
sec
• “Fade” in the response provides the basis for
evaluation
• The ratio of the height of the 4th response(T4) to
the 1st response(T1) is TOF ratio
• In partial non- depolarizing block T4/T1 ratio is
inversely proportional to degree of blockade
• In Depolarizing block, no fade occurs in TOF ratio
• Fade, in depolarizing block signifies the development of
phase II block
Train-of-Four Stimulation
Tetanic Stimulation
• Tetanic Stimulation is 50-Hz stimulation given for 5 sec
• During tetanus, progressive depletionof acetylcholine output is
balanced by increased synthesis and transfer of transmitter from it’s
mobilization stores.
• NDMR reduces the margin of safety by reducing the number of free
cholinergic receptors and also by impairing the mobilization of
acetylcholine within the nerve terminal there by contributing to the
fade in the response to tetanic and TOF stimulation.
• A frequency of 50Hz is physiological as it is similar to that generated
during maximal voluntary effort.
• During normal NM transmission and pure depolarizing block the
response is sustained
• During non- depolarizing block & phase II block the response fades
• During partial non- depolarizing block, tetanic stimulation is followed
by post-tetanic facilitation
Tetanic Stimulation
Post-Tetanic Count Stimulation
• Mobilization and enhanced synthesis of acetylcholine
continue during and after cessation of tetanic stimulation.
• Used to assess degree of NM Blockade when there is no
reaction single-twitch or TOF
• Number of post-tetanic twitch correlates inversely with
time for spontaneous recovery
• Tetanic stimulation(50Hz for 5sec.) and observing posttetanic response to single twitch stimulation at 1Hz,3sec
after end of tetanic stimulation
• Used during surgery where sudden movement must be
eliminated(e.g., ophthalmic surgery)
• Return of 1st response to TOF related to PTC
Post-Tetanic Count Stimulation
Double-Burst Stimulation
• DBS consist of two train of three impulses at
50Hz tetanic stimulation separated by 750msec
• Duration of each impulse is 0.2msec
• DBS allow manual detection of residual blockade
under clinical conditions
• Tactile evaluation of fade in DBS 3,3 is superior to
TOF as human senses DBS fade better.
• However, absence of fade by tactile evaluation to
DBS does not exclude residual NM Blockade
Double-Burst Stimulation
Non-depolarizing blockade
• Intense NM Blockade
• This phase is called “Period of no response”
• Deep NM Blockade
• Deep block characterized by absence of TOF
response but presence of post-tetanic twitches
• Surgical blockade
• Begins when the 1st response to TOF stimulation
appears
• Presence of 1 or 2 responses to TOF indicates
sufficient relaxation
Contd…
• Recovery
• Return of 4th response to TOF heralds recovery phase
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presence of spontaneous respiration is not a sign of
adequate neuromuscular recovery.
• T4/T1 ratio > 0.9 exclude clinically important residual
NM Blockade
• Antagonism of NM Blockade should not be initiated
before at least two TOF responses are observed
Depolarizing NM Blockade
• Phase I block
• Response to TOF or tetanic stimulation does not
fade, and no post-tetanic facilitation
• Phase II block
• “Fade” in response to TOF in depolarizing NM
Blockade indicates phase II block
• Occurs in pts with abnormal cholinesterase activity
and prolonged infusion of succinylcholine
Visual or tactile:
Not sensitive enough to exclude
possibility of residual neuromuscular
blockade. Fade is usually undetected until
TOF ratio values are <0.5.
Recording devices for measuring
NM Function
• Compound muscle action potential: It
is the cumulative electrical signal
generated by the individual action
potentials of the individual muscle fibres.
Electromyogram (EMG)
• It records the compound MAP via recording electrodes placed near
the mid portion or motor point of the muscle and a slightly remote
indifferent side.
• The latency of the compound MAP is the interval between stimulus
artifact and evolved muscle response.
• The amplitude of the compound MAP is proportional to the
number of muscle units that generate a MAP within the designated
time interval (epoch) and this correlates with the evoked
mechanical responses.
• For experimental studies
 The best signal is usually obtained by placing the active receiving
electrode over the belly of the muscle with the reference electrode
over the tendon insertion site
 The ground electrode is placed between the stimulating and
recording electrodes.
Mechanomyographic device
(isometric)
(Adductor pollicis force translation monitor)
• Quantifies the force of isometric contraction
• The force  electrical signal  pressure monitor and recorded.
• Key features :
a.
Alignment of the direction of thumb movement with that of the pressure
transducer.
b.
Application of consistent amount of baseline muscle tension (preload
200-300 gms)
c.
Transducer and monitor with adequate monitoring range and zeroing of
the monitor before stimulation.
DISADV:
 These devices are difficult to set up for stable and accurate
measurements
 Proper transducer orientation, isometric conditions, and application of a
stable preload are required
 Maintenance of muscle temperature within limits is important
Accelerography
(non isometric)
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This technique uses a miniature piezoelectric transducer to determine the
rate of angular acceleration.
Newton’s second law, F=m*a
Muscle must be able to move freely.
The piezoelectric crystal is distorted by the movement of the crystal inlaid
transducer which is applied to the finger and an electric current is
produced with an output voltage proportional to the deformation of the
crystal.
This is a non-isometric measurement and there are less stringent
requirements for immobilization of arm, fingers and thumb and also no
preload is necessary.
TOFguard,
TOF–watch (Organon Teknika),
Para Graph Neuromuscular Blockade Monitor (Vital signs),
Part of Datex AS/3 monitoring system (M-NMT)
KINEMYOGRAPHY
Clinical tests of Postoperative
Neuromuscular Recovery
Reliable
Unreliable
Sustained head lift for 5 sec
Sustained eye opening
Sustained leg lift for 5 sec
Protrusion of tongue
Sustained handgrip for 5 sec
Arm lifted to the opposite shoulder
Sustained “tongue depressor test”
Normal tidal volume
Maximum inspiratory pressure 40
to 50 cm H2O or greater
Normal or nearly normal vital
capacity
Maximum inspiratory pressure less
than 40 to 50 cm H2O
Limitations of NM Monitoring
• Neuromuscular responses may appear normal
despite persistence of receptor occupancy by
NMBs.
• T4:T1 ratios is one even when 40-50% receptors
are occupied
• Patients may have weakness even at TOF ratio
as high as 0.8 to 0.9
• Adequate recovery do not guarantee
ventilatory function or airway protection
• Hypothermia limits interpretation of responses
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