2. • MUSCLE RELAXANTS ARE EMPLOYED IN anesthesia
to provide muscle relaxation and/or abolish patient
movement.
• Neuromuscular block (NMB) depth should be
monitored whenever muscle relaxants are used to
avoid overdosage or underdosage during surgery
and residual NMB during recovery.
3. Equipment
• Monitoring NMB is accomplished by delivering an
electrical stimulus near a motor nerve and
evaluating the evoked muscular response
• Stimulator:Most are battery operated with a
means to check the battery status. A stimulator
may be in a module in a multiparameter monitor.
Th e ability to deliver information to an automated
record should be considered when choosing a
stimulator.
4. Essential features of PNS
• Square-wave impulse, < 0.5 msec,> 0.1 msec
duration.
• Constant current variable voltage(upto 80 mA)
• Battery powered.
• Multiple patterns of stimulation (single twitch,
train-of-four, double-burst,)
5.
6. Current
• Current, not voltage, is the determining factor in
nerve stimulation. Because skin resistance may
change, only a stimulator that automatically adjusts
its output to maintain a constant current can
ensure constant stimulation with changes in skin
resistance.
• If a motor nerve is stimulated with sufficient
current, all of the muscle fibers supplied by that
nerve will contract. Th e current required for this is
called the maximal current
7. • The reaction of a single muscle fiber to a stimulus follows an
all-or-none pattern
• In contrast, the response (the force of contraction) of the
whole muscle depends on the number of muscle fibers
activated.
• If a nerve is stimulated with sufficient intensity, all fibers
supplied by the nerve will react, and the maximum response
will be triggered.
• After administration of a neuromuscular blocking drug, the
response of the muscle decreases in parallel with the number
of fibers blocked. The reduction in response during constant
stimulation reflects the degree of neuromuscular block
8. • the stimulus must be truly maximal throughout the
whole period of monitoring; therefore, the
electrical stimulus applied is usually at least 15% to
20% greater than that necessary for a maximal
response.
• For this reason, the stimulus is said to be
supramaximal. This compensates for potential
changes in skin resistance intraoperatively and
assures constant maximal stimulation throughout
the procedure.
9. • The most frequently assessed nerve-muscle unit is
the ulnar nerve and the adductor pollicis muscle.
• A 30-mA current will produce a supramaximal
response in most patients when the ulnar nerve is
stimulated.
• Higher currents are needed with the posterior
tibial nerve.
• Patient discomfort increases with increasing
stimulating current, so a submaximal current may
be better for awake patients or those recovering
from anesthesia
10. Frequency
• Stimulus frequency is usually expressed in hertz
(Hz), which is cycles/second. One Hz is 1
cycle/second, and 0.1 Hz is equal to 1 stimulus
every 10 seconds.
11. • Waveform
• The stimulus waveform should be rectangular and
monophasic. Biphasic waves may produce
repetitive stimulation, which can underestimate
NMB depth
• Duration
• The duration should be 300 milliseconds or less. If
the pulse duration is more than 0.5 milliseconds, a
second action potential may be trigg
12. Patterns of Nerve Stimulation
• SINGLE-TWITCH STIMULATION
• In the single-twitch mode of stimulation, single
electrical stimuli are applied to a peripheral motor
nerve at frequencies ranging from 1.0 Hz (once
every second) to 0.1 Hz (once every 10 seconds.
• the subsequent muscle response is evaluated. The
response to single-twitch stimulation depends on
the frequency at which the individual stimuli are
applied
13. • There are several disadvantages associated with
single-twitch simulation.
There needs to be a control.
It cannot distinguish between a depolarizing block
and a nondepolarizing block.
Not useful to assess reversa
14.
15. TRAIN-OF-FOUR STIMULATION
• TOF stimulation consists of four supramaximal
stimuli given every 0.5 seconds (2 Hz; and each
stimulus in the train causes the muscle to contract.
• Without prior administration of a muscle relaxant,
all four responses are normally the same: the TOF
ratio is 1.0.
• During a partial nondepolarizing block, the TOF
ratio decreases (fades) and is inversely proportional
to the degree of block.
16. • With increasing degrees of block, the twitches in
train of four progressively fade starting with the
fourth T4 and one by one eventually disappear.
• Whileon recovery first to appear is T1
• The ratio of the height of the fourth response to
the first has been defined as the train of four ratio
17.
18. • During depolarizing neuromuscular blockade the
train of four does not fade significantly.
• The height of all the four twitches decreases
simultaneously
• Fade in depolarising block signifies phase II block.
19. • train-of-four ratio ( TOFR)
• is the ratio of the amplitude of the fourth response to
that of the fi rst, expressed as a percentage or a
fraction. It provides an estimation of the degree of
nondepolarizing NMB.
• In the absence of nondepolarizing block, the TOFR is
approximately 1 (100%).The deeper the block, the
lower the TOFR . Since determining the TOFR requires
that four twitches be present, it cannot be used to
monitor a deep block
20.
21. • TOF has several advantages.
• It is a more sensitive indicator of residual NMB than a
single twitch.
• A control is not necessary.
• It can distinguish between a depolarizing block and a
nondepolarizing block and is valuable in detecting
and following the development of a phase II block
following succinylcholine administration.
•
22. TETANIC STIMULATION
• Tetanic stimulation consists of high-frequency
delivery of electrical stimuli (e.g., 50-100 Hz).
• The most commonly used pattern in clinical
practice is 50-Hz stimulation given for 5 seconds,
• In normal neuromuscular transmission, the
observer detects one strong, sustained muscle
contraction, and fade after tetanic stimulation is
the basis for evaluation of nondepolarizing block.
23. • After administration of non depolarising drug
muscle will show signs of fade depending on
degree of block
• That is stimulated muscle unable to sustain
contraction
• Because at the start of tetanic stimulation, large
amounts of acetylcholine are released from
immediately available stores in the presynaptic
nerve terminal.
24. • the rate of acetylcholine release decreases until
equilibrium between mobilization and synthesis of
acetylcholine is achieved.
• When postsynapticreceptor is occupiedwith NDMR
fading occurs with decrease in amplitude following
repetitive stimulation.
25.
26. • Posttetanic facilitation (potentiation, PTF) is a
temporary increase in response to stimulation
following a tetanic stimulus.
• It is seen with a nondepolarizing but not a
depolarizing block.
• It is maximal at around 3 seconds and lasts up to 2
minutes
27. Post- tetanic count (PTC)
• Tetanus at 50 Hz for five seconds is applied
followed 3 sec later by single twitch stimulation at 1
Hz.
• The number of twitches after post tetatic
stimulation detected is called the post tetanic count
(PTC)
• Following the end of tetanus, there is an increase in
the immediately available store of acetylcholine
and the quantal content.
•
28. • Thus after tetanus, there is an increase in the
amount of transmitter released in response to
nerve stimulation and a single twitch evoked after
cessation of tetanus may be stronger than the
pretetanic control.
• Post tetanic count is a prejunctional event, the
response can vary with the nondepolarising muscle
relaxant used.
• A PTC of 8-9 suggest imminent return of TOF
29.
30. • The main application of PTC is evaluating the
degree of neuromuscular blockade when there is
no reaction to single twitch or TOF as after
administration of large dose of nondepolarizing
muscle relaxant.
• PTC is useful in predicting an appropriate time to
attempt to reversal of nondepolarising blockade
31. DOUBLE-BURST STIMULATION
• DBS consists of two short bursts of 50-Hz tetanic
stimulation separated by 750 ms, with a 0.2-ms
duration of each square wave impulse in the burst.
• The number of impulses in each burst can vary: in
the DBS3,3 mode, there are three impulses in each
of the two bursts, whereas in the DBS3,2 mode, the
first burst had three impulses and the second burst
consisted of only two impulse
32. • In nonparalyzed muscle, both muscle contractions
are of equal strength.
• In a partially paralyzed muscle, the second
response is weaker than the first and corresponds
to the typical TOFfade
• Advantage:detection of residual nondepolarizing
block under clinical conditions
33. DEPOLARIZING NEUROMUSCULAR BLOCK (PHASE I
AND II BLOCKS
• It is important to realize that during depolarizing
neuromuscular phase I block, neither fade nor
posttetanic facilitation occurred.
• After TOF stimulation, all four responses are
reduced at the same degree, no fade occurred, and
all four disappear simultaneously. Thus,
independently of the degree of depolarizing
neuromuscular block, the TOF-ratio remains 1 and
the TOF-count is either 4 or 0.phase I block;
34. • In abnormal plasma cholinesterase activity who are
given the same dose of succinylcholine undergo a
nondepolarizing-like block characterized by fade in the
response to TOF and tetanic stimulation and the
occurrence of posttetanic facilitation of transmission .
• This type of block is called a phase II block (dual,
mixed, or desensitizing block).
• In addition, phase II blocks sometimes occur in
genetically normal patients after repetitive bolus doses
or a prolonged infusion of succinylcholine.
35. Electrodes
• Stimulation is achieved by placing two electrodes
along a nerve and passing a current through them.
• Stimulation can be carried out either
transcutaneously with surface electrodes or
percutaneously with needle electrodes.
36. • 1.Surface (gel, patch, pad) electrodes have adhesive
surrounding a gelled foam pad in contact with a
metal disc, with an attachment for the electrical lead.
• They are readily available, easily applied, disposable,
self-adhering, and comfortable.
• The electrodes can be used to monitor the
electrocardiographic (ECG) tracing.
• The electrode–skin resistance decreases with a large
conducting area, as do skin burns and pain.
37. • 2.Needle Electrodes: Metal-hub needles can
also be used. Th ese electrodes run the risk that the
needle may penetrate the nerve. They are not well
accepted by awake patients.
• Disadvantages include local irritation, infection,
nerve damage especially if placed intraneurally,
diathermy burns and delivery of excessive amounts
that may induce repetative nerve firing or direct
muscle stimulation.
38. • Polarity
• Stimulators produce a direct current by using a
negative electrode and a positive electrode.
• Usually, the positive electrode is red and the negative is
black.
• 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.
39. Methods to Evaluate Evoked Responses
• Visual
• Visual assessment can be made to count the
number of responses present with a TOF stimulus,
to determine the PTC, and to detect fade with TOF
or DBS
40. • Tactile
• Tactile evaluation is accomplished by placing the
evaluator’s fingertips over the stimulated muscle
and feeling the contraction strength.
• It is more sensitive than visual monitoring for
assessing NMB by using TOF. It can be used to
evaluate the presence or absence of responses
and/or fade with TOF, double-burst, and tetanic
stimulation.
41. mechanomyography): This device objectively
quantifies the force of isometric contraction of
muscle in response to nerve stimulation.
• The force is translated into an electrical signal.
• This condition is most easily achieved by measuring
thumb movement after application of resting
tension of 200-300 g
42. • (electromyography): It records the compound
muscle action potential (MAP) (it is cumulative
electrical signal generated by individual APs of
individual muscle fibers).
43. • (acceleromyography): It uses miniature
piezoelectric transducer to determine the rate of
angular acceleration. The piezoelectric crystal is
distorted by the movement and is translated into
an electrical signal.
44. • kinemyography: 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.
45. • (phonomyography): Contraction of skeletal muscle
generates intrinsic low frequency sounds which can
be recorded with special microphones.
46. Choice of Monitoring Site
In principle, any superficially located peripheral motor
nerve can be stimulated and the response to
corresponding muscle measured.
Choosing the site of neuromuscular monitoring
depends on several factors: the site should be easily
accessible during surgery, it should allow quantitative
monitoring and finally, direct muscle stimulation should
be avoided.
Direct muscle stimulation is characterized by weak
contractions without fade persisting even at a deep
level of neuromuscular blockade.
47. • ulnar nerve is most commonly used, and the
adductor pollicis (thumb) muscle is most commonly
monitored. Because this muscle is on the side of
the arm opposite the site of stimulation, there is
little direct muscle stimula
• Stimulation at the wrist will produce thumb
adduction and fi nger flexion. Stimulation at the
elbow also produces hand adduction
48.
49.
50. • Median Nerve
• Th e median nerve is larger than the ulnar but less
superfi cial.
• It can be stimulated at the wrist by placing the
electrodes medial to where the electrodes would
be placed for ulnar nerve stimulation or at the
elbow adjacent to the brachial artery.
• This results in thumb adduction.
51. • Tibial Nerve
• To stimulate the tibial nerve at the popliteal fossa,
two stimulating electrodes are placed along the
lateral side of the popliteal fossa.
• Th e gastrocnemius muscle is stimulated.
• Using this muscle may cause significant leg
movement, which may distract the surgeon.
52. • Posterior Tibial Nerve
• To stimulate the posterior tibial nerve, electrodes
are placed behind the medial maleolus and anterior
to the Achilles tendon at the ankle
• Stimulation causes plantar flexion at the foot and
the big toe.
53. • The posterior tibial nerve off ers many advantages.
• It is especially useful in children (in whom it may
be difficult to find room on the arm because of
other monitors or invasive lines) and when the
hand is inaccessible or for other reasons such as
amputation, burns, infection, or head and neck
procedures
54.
55. • Peroneal Nerve
• To stimulate the peroneal (lateral popliteal) nerve,
electrodes are placed on the lateral aspect of the
knee
• . Stimulation causes the foot to dorsiflex
56.
57. • Facial Nerve
• The facial nerve enervates the muscles around the
eye.
• It is most useful for detecting the onset of
relaxation in the muscles of the jaw, larynx, and
diaphragm
58. • negative electrode is placed just anterior to the
inferior part of the ear lobe, and the other
electrode is placed just posterior or inferior to the
lobe .
• Stimulation at these sites will make it more likely
that muscle contractions are the result of nerve
stimulation rather than direct muscle stimulation.
59.
60. • Another way the facial nerve can be stimulated is
to place one electrode lateral to and below the
lateral canthus of the eye and the other electrode
anterior to the earlobe or 2 cm lateral to and above
the lateral canthus.
• Th is placement may result in direct muscle
stimulation
61. • When stimulating the facial nerve, low currents (20
to 30 mA) should be used. The corrugator supercilii
muscle should be observed.
• With ACG, the transducer should be placed in the
middle of the superciliary arch.
• The facial muscles are relatively resistant to NMB
drugs. Therefore, managing NMB by stimulating the
facial nerve will result in greater relaxation than
that from a limb nerve if equivalent responses are
used.
62. Using the Nerve Stimulator to Monitor
Neuromuscular Block
• Before Induction
• 1. Prior to induction, the stimulator should be
connected to electrodes that are positioned over
the selected nerve.
• 2. Electrode sites should be dry and free of
excessive hair or scar tissue or other lesions. Th e
skin should be thoroughly cleansed with a solvent
such as alcohol and then completely dried and
rubbed briskly with a gauze pad until a slight
redness is visible.
63. Induction
• 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.
• After induction but before administering any
muscle relaxants, the stimulator should be turned
ON and set to deliver single-twitch stimuli at 0.1 Hz.
64. • Applying stimulation more frequently will make it
appear that the NMB onset time is shorter.
• Th e stimulator output should be increased until
the response does not increase with increasing
current and then increased 10% to 20%.
• If maximal stimulation is not achieved with a
current of 50 to 70 mA, the electrodes should be
checked for proper placement
65. Intubation
• Complete relaxation of the jaw, laryngeal and
pharyngeal muscles, and diaphragm is needed for
optimal intubating conditions and to reduce the
risk of trauma.
• It should be kept in mind that the response to
intubation is a function of both muscular block and
the level of anesthesia.
• It is possible to intubate a patient with less than
complete paralysis if suffi cient anesthetic depth is
present.
66. • onset of NMB is faster in centrally located muscles
such as the diaphragm, facial, laryngeal, and jaw
muscles than peripheral muscles such as the
adductor pollicis.
• diaphragm, eye muscles, and most laryngeal
muscles are more resistant to nondepolarizing
relaxants than peripheral muscles.
67. • The diaphragm is resistant to succinylcholine,
though the laryngeal muscles are sensitive to it.
• The masseter muscle is relatively sensitive to both
nondepolarizing and depolarizing relaxants. It often
reacts with increased tone instead of relaxation to
succinylcholine, particularly in children
68. • Monitoring the eye muscle response will refl ect
the time of onset and the level of NMB at the
airway musculature more closely than monitoring
peripheral muscles
69. Maintenance
• During maintenance, the stimulator can be used to
titrate the relaxant dosage to the needs of the
operative procedure, so both under- and
overdosage are avoided.
• Too deep an NMB may make it diffi cult to reverse
the relaxant at the termination of the anesthetic.
• Underdosage may result in inadequate relaxation
or undesirable patient movem
70. • TOF is commonly regarded as the most useful pattern
for monitoring NMB during maintenance.
• If no response is present, further administration of
relaxants is not indicated.
• If two responses are present, abdominal relaxation
may be adequate using balanced anesthesia
• Presence of three twitches is usually associated with
adequate relaxation if a volatile anesthetic agent is
used
71. Recovery and Reversal
• Antagonism with neostigmine should not be
initiated before at least all four responses to TOF
stimulation are present.
• With a large dose of neostigmine (e.g., 5 mg/70 kg),
the median time to achieve a TOF ratio of 0.90 is 15
to 20 minutes, and
• it will take approximately 90 to 120 minutes to
achieve a TOF ratio of 0.90 in 95% of the patients
after an intermediate-acting neuromuscular
blocking drug (e.g., rocuronium)
72. • Three different doses of sugammadex are
recommended according to the level of block.
• A large dose (16 mg/kg) is given during intense
block (no response to PTC stimulation),
• a medium dose (4 mg/ kg) during deep block (at
least one response to PTC),
• and a low dose (2 mg/kg) during moderate block
(two or more responses to TOF stimulation)
73. • all levels of neuromuscular block are reversed
within 2 to 5 minutes
• Only a TOF ratio of 0.90 to 1.00 measured by
objective monitoring ensures a low risk of clinically
significant residual block
