2. 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.
3. Why do we Monitor?
Residual post-op NM Blockade
– 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
4. 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
• Surgeries requiring profound NM blockade
5. Various ways of nerve
stimulation
• Electrical: Most commonly used in
clinical practice.
• Magnetic: Less painful and does not
require physical contact with body.
6. Principles of Peripheral Nerve
Stimulation
• Each muscle fiber to a stimulus follows an all-or-
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
7. Essential features of PNS
• Shape of stimulus should be monophasic and
rectangular i.e Square-wave stimulus.
• 0.2- 0.3 msec duration so it falls within absolute
refractory period of motor unit in the nerve.
• Constant current variable voltage
• Battery powered.
• Digital display of delivered current.
• Audible signal on delivery of stimulus.
• Audible alarm for poor electrode contact.
• Multiple patterns of stimulation (single
twitch,train-of-four, double-burst, post-tetanic
count).
8. • 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
9. • 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.
• Maximal current:current which generate response in
all muscle fibre
• Supramaximal current :
• It is approximately 25% 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).
10. 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
• Require less current
11. 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
12. VARIOUS SITE USED FOR NM MONITORING
• Ulnar nerve: MOST COMMON
SITE
• 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
13. • 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
14. • 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) 2-
3cm proximal to the
negative electrode
• • Response: Flexor hallucis
brevis muscle – plantar
flexion of big toe
16. 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 response is noted &
compared with subsequent responses
• Response will only be depressed when NM
blocker occupies 75% receptor
17. • Used to assess potency of drugs
• Useful before induction to determine level at
which supramaximal stimulus obtained
• Useful to determine onset of NM block
• In both depolarising & non depolarising blocks
there is progressive decrease in twitch height
• So can not differentiate between depolarising &
non depolarising NM blocker
• Major limitation is need to measure control
twitch before NM blocker i.e. prerelaxant
control response is necessary
19. 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 so
equal depression in twitch height
• Fade, in depolarizing block signifies the development of
phase II block
21. 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
23. 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 post-tetanic
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
25. 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
27. 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
28. Contd…
• Recovery
• Return of 4th response to TOF heralds recovery phase
• 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
29.
30. 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
31. Visual or tactile:
Not sensitive enough to exclude
possibility of residual neuromuscular
blockade. Fade is usually undetected until
TOF ratio values are <0.5.
32. 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.
33. 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.
34.
35. 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
36. Accelerography
(non isometric)
• 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)
37.
38. 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
39.
40.
41. 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
