Neuromuscular monitoring

NEUROMUSCULAR
MONITORING
Presented By:
Siddhanta Choudhury
1st yr PG
Dept. of Anesthesiology
Guided By:
Dr. C.R. Panigrahi
Asst. Professor
Dept. of Anesthesiology

INTRODUCTION
■ Neuromuscular blockers (NMBs) are widely used in anesthesia practice.
Simple quantitative method to monitor their effects is desirable.
Neuromuscular junction (NMJ) monitors have proven to be useful
adjuncts in clinical anesthesiology practice.
■ Traditionally, anesthesiologists evaluated the degree of neuromuscular
block during and after anesthesia using clinical criteria alone. But the
recommendation for application of neuromuscular monitoring to
patients receiving NMBs is based on two important issues:
– first, on the variable individual response to muscle relaxants and
– second, because of the narrow therapeutic window.
■ There is no detectable block until 75 to 85% of receptors are occupied
and paralysis is complete at 90 to 95% receptor occupancy.Therefore
adequate muscle relaxation corresponds to a narrow range of 85 to 90%
receptor occupancy.

■ Neuromuscular monitoring permits administration of NMBs such that
optimal surgical relaxation is achieved and yet the block reverses
spontaneously or reversed reliably and quickly with antagonists.
■ It has been shown that when monitoring of NMJ function is not
performed and clinical criteria alone are used, up to 42% of the patients
are inadequately reversed upon arrival to the recovery room.
■ Residual neuromuscular block is a major risk factor for many critical
events in the immediate postoperative period such as ventilatory
insufficiency, hypoxemia and pulmonary infections.
■ The use of short acting NMBs and wide spread use of perioperative NMJ
monitoring was found to be helpful in reducing these complications.
■ The most satisfactory method for reliably monitoring neuromuscular
function is the stimulation of an appropriate nerve using a peripheral
nerve stimulator and observation of evoked response in the muscle
supplied.
■ In 1958, Christie and Churchill-Davidson described how nerve
stimulators could be used to assess neuromuscular function objectively
during anesthesia.

Principles of Peripheral
Nerve Stimulation
■ The reaction of a single muscle fiber to a stimulus
follows an all-or-none pattern.
■ In contrast, the response of the whole muscle depends
on the number of muscle fibers activated.
■ The stimulus must be truly maximal throughout the
period of monitoring; therefore, the electrical stimulus
applied is usually at least 20% to 25% above that
necessary for a maximal response.

Features of Neurostimulation
■ The key features of exogenous nerve stimulation are:
– Nerve stimulator: A battery powered device that
delivers depolarizing current via the electrodes
– Constant current and variable voltage
– Stimulus strength: The depolarizing intensity of
stimulating current.
– depends on:
1. duration (pulse width) of the stimulus
2. current intensity

– Pulse width: duration of the individual impulse
delivered by the nerve stimulator.
– should be <0.5 msec and >0.1 msec
– Pulse width >0.5 msec extends beyond the refractory
period of the nerve resulting in repetitive firing.
– Current intensity: Ranges from 0-80 mA
– The intensity reaching the nerve is determined by:
1. the voltage generated
2. resistance and impedance of the electrodes, skin
and underlying tissues.

– Threshold current : The lowest current required to
depolarize the most sensitive fibers in a given nerve
bundle to elicit a detectable muscle response
– Supramaximal current : Approximately 10-20%
higher intensity than the current required to
depolarize all fibres in a particular nerve bundle.
– 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).
– Single twitch is commonly repeated at 10 second
intervals i.e. 0.1 Hz and tetanic stimulation commonly
consists of 50 impulses/sec, i.e. 50 Hz.

Types of Peripheral Nerve
Stimulation
Two types of stimulation can be used: electrical and magnetic.
■ Magnetic nerve stimulation is less painful and does not
require physical contact with the body.
■ However, the equipment required is bulky and heavy
■ It cannot be used for train-of-four (TOF) stimulation, and
it is difficult to achieve supramaximal stimulation with this
method.

The Nerve Stimulator
■ A number of contemporary monitors are available commercially.The desirable
features of a nerve stimulator are listed below:
■ Essential features
– Square-wave impulse, < 0.5 msec,> 0.1 msec duration.
– Constant current variable voltage.
– Battery powered
– Multiple patterns of stimulation (single twitch, train-of-four, double-burst,
post-tetanic count).
■ Optional Features
– Rheostat for adjustable current output.
– Polarity output indicator.
– Ability to calculate and display fade ratio and percentage depression of
single twitch.
– High output (80-100 mA) and low output (<5 mA) sockets.
– Audible signal with each stimulus.
– Alarm for excessive impedance, lead disconnect, low battery.
– Battery charge indicator.

The Stimulating Electrodes
■ Electrical impulses are transmitted from stimulator to
nerve by means of surface or needle electrodes, the
former being the more commonly used in clinical
anesthesia.
■ Normally, disposable pregelled silver or silver
chloride surface electrodes are used.The actual
conducting area should be small, approximately 7 to
11 mm in diameter

Sites of Nerve Stimulation
■ In principle, any superficially located peripheral motor
nerve may be stimulated.
■ In clinical anesthesia, the ulnar nerve is the most popular
site.
■ The median, posterior tibial, common peroneal, and
facial nerves are also sometimes used.
■ For stimulation of the ulnar nerve, the electrodes are best
applied to the volar side of the wrist

■ When the temporal branch of the facial nerve is
stimulated, the negative electrode should be placed over
the nerve, and the positive electrode should be placed
somewhere else over the forehead.

 The posterior
tibial nerve may
be stimulated as it
comes behind the
medial malleolus,
caused plantar
flexion of the
great toe and foot.
 The peroneal
nerve and lateral
popliteal nerve
elicit dorsi flexion
of the foot

■ The diaphragm is among the most resistant of all muscles to both
depolarizing and nondepolarizing neuromuscular blocking drugs.
■ requires 1.4 to 2.0 times as much muscle relaxant as the adductor
pollicis muscle for an identical degree of blockade .
■ Also of clinical significance is that onset time is normally shorter
for the diaphragm than for the adductor pollicis muscle and the
diaphragm recovers from paralysis more quickly than the
peripheral muscles do .
■ The other respiratory muscles are less resistant than the
diaphragm, as are the larynx and the corrugator supercilii
muscles.

■ Most sensitive are the abdominal muscles, the orbicularis
oculi muscle, the peripheral muscles of the limbs, and the
geniohyoid, masseter, and upper airway muscles.
■ From a practical clinical point of view, it is worth noting that
– the response of the corrugator supercilii to facial nerve
stimulation reflects the extent of neuromuscular blockade
of the laryngeal adductor muscles and abdominal muscles
better than the response of the adductor pollicis to ulnar
nerve stimulation does
– the upper airway muscles seem to be more sensitive than
the peripheral muscles.

Patterns of Nerve
Stimulation ■ Single-
twitch
■ TOF
■ Tetanic
■ Post-
tetanic
count (PTC)
■ Double-
burst
stimulation
(DBS).

PostTetanic Facilitation
■ During partial nondepolarizing blockade, tetanic nerve
stimulation is followed by a post-tetanic increase in twitch
tension (i.e., post-tetanic facilitation of transmission).
■ This event occurs because the increase in mobilization and
synthesis of acetylcholine caused by tetanic stimulation
continues for some time after discontinuation of stimulation.
■ The degree and duration of post-tetanic facilitation depend
on the degree of neuromuscular blockade, with post-tetanic
facilitation usually disappearing within 60 seconds of
tetanic stimulation.

Post-Tetanic Count
Stimulation

■ The PTC method is mainly used to assess the degree
of neuromuscular blockade when there is no
reaction to single-twitch orTOF nerve stimulation,
as may be the case after injection of a large dose of a
nondepolarizing neuromuscular blocking drug.
■ However, PTC can also be used whenever sudden
movements must be eliminated (e.g., during
ophthalmic surgery).

■ The necessary level of blockade of the adductor pollicis
muscle to ensure paralysis of the diaphragm depends on the
type of anesthesia and, in the intensive care unit, on the level
of sedation.
■ To ensure elimination of any bucking or coughing in response
to trachea-bronchial stimulation, neuromuscular blockade of
the peripheral muscles must be so intense that no response
to post-tetanic twitch stimulation can be elicited (PTC 0)
■ The response to PTC stimulation depends primarily on the
degree of neuromuscular blockade.

■ It also depends on the :-
1. frequency and duration of tetanic stimulation,
2. the length of time between the end of tetanic stimulation and
the first post-tetanic stimulus,
3. the frequency of the single-twitch stimulation,
4. the duration of single-twitch stimulation before tetanic
stimulation.
■ When the PTC method is used, these variables should be kept
constant.
■ In addition, because of possible antagonism of neuromuscular
blockade in the hand, tetanic stimulation should not be
performed more often than every 6 minutes.

Adductor pollicis: Advantages vs
Disadvantages
ADVANTAGES DISADVANTAGES
The risk of overdosing the patient
decreases if the response of a
relatively sensitive muscle is used as a
guide to the administration of muscle
relaxants during surgery
Even total elimination of
the response to single-
twitch andTOF
stimulation does not
exclude the possibility of
movement of the
diaphragm, such as
hiccupping and coughing
During recovery, when the adductor
pollicis has recovered sufficiently, it
can be assumed that no residual
neuromuscular blockade exists in the
diaphragm or in other resistant
muscles

Recording of Evoked Responses
■ Five methods are available:
1. Measurement of the evoked mechanical response of the muscle
(mechanomyography [MMG]),
2. Measurement of the evoked electrical response of the muscle
(electromyography [EMG]),
3. Measurement of acceleration of the muscle response
(acceleromyography [AMG]),
4. Measurement of the evoked electrical response in a
piezoelectric film sensor attached to the muscle (piezoelectric
neuromuscular monitor [PZEMG]
5. Phonomyography [PMG]).

Mechanomyography
■ The mechanomyogram (MMG) is the mechanical signal
observable from the surface of a muscle when the muscle is
contracted.
■ At the onset of muscle contraction, gross changes in the
muscle shape cause a large peak in the MMG.
■ Subsequent vibrations are due to oscillations of the muscle
fibres at the resonance frequency of the muscle.
■ A requirement for correct and reproducible measurement of
evoked tension is that the muscle contraction be isometric.

■ In clinical anesthesia, this condition is most easily achieved by
measuring thumb movement after the application of a resting
tension of 200 to 300 g (a preload) to the thumb.
■ When the ulnar nerve is stimulated, the thumb (the adductor pollicis
muscle) acts on a force-displacement transducer.
■ The force of contraction is then converted into an electrical signal,
which is amplified, displayed, and recorded.
■ The arm and hand should be rigidly fixed, and care should be
taken to prevent overloading of the transducer.
■ In addition, the transducer should be placed in correct relation to
the thumb (i.e., the thumb should always apply tension precisely
along the length of the transducer).

Electromyography
■ EMG is a technique for evaluating and recording the
electrical activity produced by skeletal muscles.
■ Evoked EMG records the compound action
potentials produced by stimulation of a peripheral
nerve.

■ The evoked EMG response is most often obtained from muscles
innervated by the ulnar or the median nerves.
■ Most often, the evoked EMG response is obtained from the thenar
or hypothenar eminence of the hand or from the first dorsal
interosseous muscle of the hand, preferably with the active
electrode over the motor point of the muscle .
■ The signal picked up by the analyzer is processed by an amplifier, a
rectifier, and an electronic integrator. The results are displayed
either as a percentage of control or as aTOF ratio.
■ Evoked electrical and mechanical responses represent different
physiologic events. Evoked EMG records changes in the electrical
activity of one or more muscles, whereas evoked MMG records
changes associated with excitation-contraction coupling and
contraction of the muscle as well.

ADVANTAGES DISADVANTAGES
Equipment for measuring evoked EMG
responses is easier to set up
Although high-quality recordings are possible
in most patients, the results are not always
reliable.
Improper placement of electrodes may result
in inadequate pickup of the compound EMG
signal.
The response reflects only factors
influencing neuromuscular transmission
Direct muscle stimulation sometimes occurs.
If muscles close to the stimulating electrodes
are stimulated directly, the recording
electrodes may pick up an electrical signal
even though neuromuscular transmission is
completely blocked.
The response can be obtained from
muscles not accessible to mechanical
recording.
EMG response often does not return to the
control value.
Very sensitive to electrical interference,
such as that caused by diathermy.

Acceleromyography
■ A piezoelectric myograph is used to measure the force
produced by a muscle after it has undergone nerve stimulation.
■ Measure muscle activity using a miniature piezoelectric
transducer that is attached to the stimulated muscle.
■ A voltage is created when the muscle accelerates and that
acceleration is proportion to force of contraction.
■ More costly than the more common twitch monitors, but have
been shown to better alleviate residual blockade and
associated symptoms of muscle weakness, and to improve
overall quality of recovery.

■ When an accelerometer is fixed
to the thumb and the ulnar
nerve is stimulated, an electrical
signal is produced whenever the
thumb moves.
■ This signal can be analyzed in a
specially designed analyzer.
■ Transducer is fastened to the
thumb and the stimulating
electrodes.
■ On the display, the train-of-four
(TOF) ratio is given in
percentage.

■ When AMG is used with a free-moving thumb, as originally
suggested, wide limits of agreements in twitch height (T1)
andTOF ratio and differences in the onset and recovery
course of blockade between AMG and MMG have been
found.
■ Moreover, the AMG controlTOF ratio is consistently higher
than when measured with a force-displacement transducer.
■ In accordance with this, several studies have indicated that
when using AMG, theTOF ratio indicative of sufficient
postoperative neuromuscular recovery is 1.0 rather than 0.9
as when measured by MMG or EMG in the adductor pollicis
muscle.

■ Originally claimed advantages of the method, that fixation
of the hand could be reduced to a minimum as long as the
thumb could move freely.
■ In daily clinical practice it is often not possible to ensure that
the thumb can move freely and that the position of the
hand does not change during a surgical procedure.
■ The evoked response may therefore vary considerably.
■ Several solutions have been proposed, and on-going clinical
research indicates that the use of an elastic preload on the
thumb may improve the agreement between results
obtained with AMG and MMG.

■ Hand adaptor (elastic
preload) for theTOF-
Watch transducer

Piezoelectric Neuromuscular
Monitors
■ The technique of the
piezoelectric monitor is
based on the principle
that stretching or
bending a flexible
piezoelectric film (e.g.,
one attached to the
thumb) in response to
nerve stimulation
generates a voltage
that is proportional to
the amount of
stretching or bending.

Phonomyography
■ Contraction of skeletal muscles
generates intrinsic low-
frequency sounds, which can be
recorded with special
microphones.
■ What does make PMG
interesting, however, is that in
theory the method can be
applied not only to the adductor
pollicis muscle but also to other
muscles of interest such as the
diaphragm, larynx, and eye
muscles.
■ In addition, the ease of
application is attractive.

Evaluation of Recorded
Evoked Responses
■ Nerve stimulation in clinical anesthesia is usually
synonymous with TOF nerve stimulation.
■ Therefore, the recorded response to this form of
stimulation is used to explain how to evaluate the
degree of neuromuscular blockade during clinical
anesthesia.

Nondepolarizing
Neuromuscular Blockade
■ After injection of a nondepolarizing neuromuscular
blocking drug in a dose sufficient for smooth tracheal
intubation,TOF recording demonstrates four phases or
levels of neuromuscular blockade:
1. Intense blockade,
2. Deep blockade,
3. Moderate or surgical blockade,
4. Recovery

■ In clinical anesthesia, aTOF ratio of 0.70 to 0.75, or even 0.50, has been
thought to reflect adequate recovery of neuromuscular function.
■ However, theTOF ratio, whether recorded mechanically or by EMG,
must exceed 0.80 or even 0.90 to exclude clinically important residual
neuromuscular blockade.
■ Moderate degrees of neuromuscular blockade decrease chemoreceptor
sensitivity to hypoxia and thereby lead to insufficient response to a
decrease in oxygen tension in blood.
■ Moreover, residual blockade (TOF < 0.90) is associated with functional
impairment of the pharyngeal and upper esophageal muscles, which
most probably predisposes to regurgitation and aspiration of gastric
contents.

■ Accordingly, residual blockade (TOF < 0.70) caused by the
long-acting muscle relaxant pancuronium is a significant risk
factor for the development of postoperative pulmonary
complications .
■ Even in volunteers without sedation or impaired
consciousness, aTOF ratio of 0.9 or less may impair the
ability to maintain the airway.
■ Adequate recovery of neuromuscular function requires
return of an MMG or EMGTOF ratio to 0.90 or greater,
which cannot be guaranteed without objective
neuromuscular monitoring

Correlation with receptor occupancy

Depolarizing Neuromuscular
Blockade (Phase I and II Blocks)
PHASE I BLOCK
■ Patients with normal plasma cholinesterase activity who are given a
moderate dose of succinylcholine (0.5 to 1.5 mg/kg) undergo a typical
depolarizing neuromuscular block
■ The response to TOF or tetanic stimulation does not fade, and no post-
tetanic facilitation of transmission occurs).
PHASE II BLOCK
■ In contrast, some patients with genetically determined abnormal
plasma cholinesterase activity who are given the same dose of
succinylcholine undergo a nondepolarizing-like block characterized by
fade in the response toTOF and tetanic stimulation and the occurrence
of post-tetanic facilitation of transmission
■ In addition, phase II blocks sometimes occur in genetically normal
patients after repetitive bolus doses or a prolonged infusion of
succinylcholine.

■ In normal patients, a phase II block can be antagonized by administering a
cholinesterase inhibitor a few minutes after discontinuation of
succinylcholine.
■ In patients with abnormal genotypes, however, the effect of intravenous
injection of an acetylcholinesterase inhibitor (e.g., neostigmine) is
unpredictable.
■ For example, neostigmine can
I. Potentiate the block dramatically,
II. Temporarily improve neuromuscular transmission, and then potentiate
the block
III. Partially reverse the block,
■ All depending on the time elapsed since administration of succinylcholine
and the dose of neostigmine given.
■ Therefore, unless the cholinesterase genotype is known to be normal,
antagonism of a phase II block with a cholinesterase inhibitor should be
undertaken with extreme caution. Even if neuromuscular function improves
promptly, patient surveillance should continue for at least 1 hour.

Use of Nerve Stimulators
Without Recording
Equipment■ First, for supramaximal stimulation, careful cleansing of the
skin and proper placement and fixation of electrodes are
essential.
■ Second, every effort should be taken to prevent central
cooling, as well as cooling of the extremity being
evaluated. Both central and local surface cooling of the
adductor pollicis muscle may reduce twitch tension and the
TOF ratio.

■ Peripheral cooling may affect
1. Nerve conduction,
2. Decrease the rate of release of acetylcholine and muscle
contractility,
3. Increase skin impedance, and
4. Reduce blood flow to muscles, thus decreasing the rate of
removal of muscle relaxant from the neuromuscular junction.
■ Third, when possible, the response to nerve stimulation should be
evaluated by feel and not by eye, and the response of the thumb
(rather than response of the fifth finger) should be evaluated.
■ Finally, the different sensitivities of various muscle groups to
neuromuscular blocking agents should always be kept in mind.

Use of a Peripheral Nerve Stimulator
During Induction of Anesthesia
■ The nerve stimulator should be attached to the patient before
induction of anesthesia but should not be turned on until after the
patient is unconscious.
■ Single-twitch stimulation at 1 Hz may be used initially when
seeking supramaximal stimulation.
■ However, after supramaximal stimulation has been ensured and
before muscle relaxant is injected, the mode of stimulation should
be changed toTOF or 0.1Hz twitch stimulation.
■ Then, after the response to this stimulation has been observed (the
control response), the neuromuscular blocking agent is injected.
■ Although the trachea is often intubated when the response toTOF
stimulation disappears, postponement of this procedure for 30 to
90 seconds, depending on the muscle relaxant used, usually
produces better conditions.

Use of a Peripheral Nerve
Stimulator During Surgery
■ If tracheal intubation is facilitated by the administration of
succinylcholine, no more muscle relaxant should be given
until the response to nerve stimulation reappears or the
patient shows other signs of returning neuromuscular
function.
■ If plasma cholinesterase activity is normal, the muscle
response toTOF nerve stimulation reappears within 4 to 8
minutes.
■ When a nondepolarizing neuromuscular drug is used for
tracheal intubation, a longer-lasting period of intense
blockade usually follows.
■ During this period of no response toTOF and single-twitch
stimulation, the time until return of response toTOF
stimulation may be evaluated by PTC.

■ For most surgical procedures requiring muscle relaxation, twitch
depression of approximately 90% will be sufficient, provided that the
patient is adequately anesthetized.
■ If a nondepolarizing relaxant is used, one or two of the responses toTOF
stimulation can be felt.
■ Because the respiratory muscles (including the diaphragm) are less
sensitive to neuromuscular blocking agents than the peripheral muscles
are, the patient may breathe, hiccup, or even cough at this depth of
blockade.
■ To ensure paralysis of the diaphragm, neuromuscular blockade of the
peripheral muscles must be so intense that the PTC is zero in the thumb.
■ An added advantage of keeping the neuromuscular blockade at a level of
one or two responses toTOF stimulation is that antagonism of the block
is facilitated at the end of surgery.

Use Of A Peripheral Nerve Stimulator During
Reversal Of Neuromuscular Blockade
■ Antagonism of nondepolarizing neuromuscular blockade with a
cholinesterase inhibitor such as neostigmine should probably not be
initiated before at least two responses toTOF stimulation are present
or before obvious clinical signs of returning neuromuscular function are
seen.
■ Reversal of neuromuscular blockade will not be hastened and may
possibly be delayed by giving neostigmine when no response to
peripheral nerve stimulation is present.
■ Conversely, to achieve rapid reversal (within 10 minutes) to aTOF ratio of
0.7 in more than 90% of patients, three and preferably four responses
should be present at the time of neostigmine injection.
■ During recovery of neuromuscular function, when all four responses to
TOF stimulation can be felt, an estimation of theTOF ratio may be
attempted.
■ Greater sensitivity is achieved with DBS3,3, but even absence of manual
fade in the DBS3,3 response does not exclude clinically significant residual
blockade.

ClinicalTests of
Postoperative
Neuromuscular RecoveryReliable 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

Tongue DepressorTest
■ Its a sensitive and useful bedside test to asses the adequate recovery
of neuromuscular function.
■ At a TOF ratio of 0.70 most volunteers cannot retain a wooden tongue
depressor between their incisor teeth against even minimal effort to
remove it.
■ In general, full return of masseter strength does not occur until the
TOF ratio exceeds 0.80.
■ The practical implication of this is that, if at the end of a case it is
difficult or impossible to remove a patient’s bite block, it is highly
likely that adequate neuromuscular recovery has already taken place.

When to Use a Peripheral
Nerve Stimulator
■ Good evidence-based practice dictates that clinicians
should always quantify the extent of neuromuscular
recovery by objective monitoring.
■ At a minimum, the TOF ratio should be measured
during recovery whenever a nondepolarizing
neuromuscular block is not antagonized.

Which patients should be monitored?
■ Monitoring is advisable particularly in conditions where the
pharmacokinetics and pharmacodynamics of NMBs are
altered significantly as listed below:
1. Severe renal, liver disease
2. Neuromuscular disorders such as myasthenia gravis,
myopathies, and upper and lower motor neuron lesions
3. Patients with severe pulmonary disease or marked obesity
to ensure adequate recovery of skeletal muscle function
4. Neuromuscular blockade achieved with continuous
infusion of NMBs
5. Patients receiving long-acting NMBs
6. Patients undergoing lengthy surgical procedures

How then to evaluate and, as far as
possible, exclude a clinically
significant postoperative block?
■ First, long-acting neuromuscular blocking agents should not
be used.
■ Second, the tactile response toTOF nerve stimulation
should be evaluated during surgery.
■ Third, if possible, total twitch suppression should be avoided.
The block should be managed so that there is always one or
two tactileTOF responses.

■ Fourth, the block should be antagonized at the end of
the procedure, but reversal should not be initiated before
at least two and preferably three or four responses to
TOF stimulation are present.
■ Fifth, during recovery, tactile evaluation of the
response to DBS is preferable to tactile evaluation of the
response toTOF stimulation because it is easier to feel
fade in the DBS than in theTOF response.
■ Sixth, the clinician should recognize that absence of
tactile fade in both theTOF and DBS responses does not
exclude significant residual blockade. !!!
■ Finally, reliable clinical signs and symptoms of residual
blockade should be considered in relation to the
response to nerve stimulation.

LIMITATIONS OF NEUROMUSCULAR
MONITORING
■ Despite the important role of NMJ monitoring in anesthesia
practice, it is necessary to use a multifactorial approach for the
following reasons:
1. Neuromuscular responses may appear normal despite
persistence of receptor occupancy by NMBs.T4:T1 ratio is
one even when 40-50% of the receptors are occupied.
2. Because of wide individual variability in evoked responses,
some patients may exhibit weakness atTOF ratio as high as
0.8 to 0.9.
3. The established cut-off values for adequate recovery do not
guarantee adequate ventilatory function or airway
protection.
4. Increased skin impedance resulting from perioperative
hypothermia limits the appropriate interpretation of evoked
responses.

CONCLUSION
■ Many anesthesiologists do not agree with
extensive use of NMJ monitors and argue that
patients can be managed satisfactorily without
the devices.
■ Although not included under the standards for
basic anesthetic monitoring by the American
Society of Anesthesiologists, the real value of
such monitors lies in the fact that they guide
the optimal management of patients receiving
NMBs.

REFERENCES
■ Millers Anesthesia 8th Edition
■ Dr. D. Padmaja, Dr. Srinivas Mantha.
Monitoring of Neuromuscular Junction.
IJA.2002;46(4) : 279-288
■ Internet Sources

Neuromuscular monitoring

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