Neuro muscular monitoring

1. Neuro muscularMonitoring
Dr. Anup Kumar Harichandan PG 2nd
yr

2. Objectives of NMMonitoring
• 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. • Neuromuscular monitoring permit optimal
surgical relaxation and reverses the block
spontaneously or revesed quickly with
antagonists.
• There is no detectable block until 75 to 85% of
Ach receptors are occupied and paralysis is
complete at 90 to 95% Ach receptor
occupancy.

4. Need of Monitoring
 To prevent residual post-op NM blockade
• Decrease chemo receptor sensitivity to
hypoxia
• Functional impairment of pharyngeal and
upper esophageal muscles
• Impaired ability to maintain the airway
• Increased risk for post-op pulmonary
complications

5. Difficult to exclude clinically significant
residual paralysis by clinical evaluation
Absence of tactile fade to TOF , tetanic
stimulation, DBS does not exclude
significant residual blockade
Variable individual response to muscle
relaxants
Narrow therapeutic window

6. Principles of Peripheral Nerve
Stimulation
• Each muscle fiber to a stimulus follows an all-or-
none pattern
• In contrast, 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. Features of Neurostimulation
• Nerve stimulator- device that delivers
depolarizing current via electrodes
• Essential Features
• Monophasic, Square-wave impulse, 0.1-0.5msec
• Constant current variable voltage
• Battery powered
• Multiple patterns of stimulation

8. • Stimulus strength- it is the depolarizing intensity of
stimulating current
• Pulse width-duration of the individual impulse
delivered by nerve stimulator
• Threshold current –lowest current required to
depolarize a nerve fiber
• Supramaximal current-it is 10 -20% higher
intensity than the current required to depolarize all
fibers in a nerve bundle
• Stimulus Frequency- rate at which each impulse is
repeated in cycles per sec(Hz)

9. Electrodes
• Surface electrodes
• More commonly used than needle 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

10. Patterns of nerve stimulation
For evaluation of neuromuscular function,
the most
commonly used patterns of electrical nerve
stimulation are
•Single-twitch stimulation
•Train-of-Fourstimulation (TOF)
•Tetanic stimulation
•Post-tetanic count stimulation (PTC)

11. Single-twitch stimulation
• This is the simplest form of neuro
stimulation,in which single supra-maximal
electrical stimuli are applied to a
peripheral motor nerve at frequencies
ranging from 1.0 Hz to 0.1 Hz
• Height of response depends on the
number of unblocked junctions
• Does not detect receptor block of <70%
• Used to assess potency of drugs

12. • Pattern of electrical stimulation and evoked muscle responses to single-twitch nerve
stimulation (at frequencies of 0.1 to 1.0 Hz) after injection of nondepolarizing (Non-
dep.) and depolarizing (Dep.) neuromuscular blocking drugs (arrows).
Pattern of electrical stimulation and evoked muscle
responses to single-twitch nerve stimulation

13. Train-of-Fourstimulation (TOF)
• This is a popular mode of stimulation for
clinical monitoring of neuromuscular junction
first described by Ali et al.
• Four supra maximal stimuli are given every
0.5 sec (2 Hz)
• When used continuously, each set (train) of
stimuli is normally repeated every 10th to 20th
second.
• “Fade” in the response provides the basis for

14. • The ratio of the height of the 4th
response(T4) to
the 1st
response(T1) is TOF ratio
• In partial non- depolarizing block TOF ratio
(T4/T1) is inversely proportional to degree of
blockade
• In partial depolarizing block, no fade occurs in
TOF ratio ,ideally it is approx. one.
• Fade, in depolarizing block signifies the
development of phase II block .

15. Pattern of electrical stimulation and evoked muscle responses to
TOF nerve stimulation

16. ADVANTAGES OFTOFSTIMULATION
• This pattern of stimulation can be applied at
anytime during the neuromuscular block and
can provide quantification of depth of block
without the need for control measurement
before relaxant administration.
• It is more sensitive to lesser degree of receptor
occupancy than single twitch.

17. The relatively low frequency allows response to be
evaluated manually or visibly.
There is no post tetanic facilitation therefore can be
repeated every 10 to 12 sec.
It may be delivered at sub maximal current which is
less painful and is associated with same degree of
fade.

18. Tetanic stimulation
• Tetanic stimulation consists of very rapid (e.g.,
30-, 50-, or 100-Hz) delivery of electrical
stimuli.
• The most commonly used pattern in cinical
practice is 50-Hz stimulation given for 5 sec
• During normal NM transmission and pure
depolarizing block the response is sustained
• During non- depolarizing block & phase II
block the response fades

19. During tetanus, progressive depletion of
acetylcholine output is balanced by increased
synthesis and transfer of transmitter from its
mobilization stores.
High frequency stimulation (50Hz or more)
results in sustained or tetanic contraction of
the muscle during normal neuromuscular
transmission despite decrement in
acetylcholine release.

20. • During partial non- depolarizing block, tetanic
stimulation is followed by post-tetanic facilitation
• It 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

21. The presence of nondepolarizing muscle relaxants
reducing the number of free cholinergic receptors and
also by impairing the mobilization of acetylcholine
within the nerve terminal contributes 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. Fade
is first noted at 70% receptor occupancy.

22. Pattern of stimulation and evoked muscle responses to tetanic (50-Hz)
nerve stimulation for 5 seconds (Te) and post-tetanic twitch
stimulation (1.0-Hz)

23. DISADVANTAGES
• The post tetanic facilitation depends on frequency
and duration of block
• It is very painful and therefore not suitable for un
anaesthetised patients.

24. Post-tetanic count stimulation
(PTC)
Tetanus at 50 Hz for five seconds is applied
followed 3 sec later by single twitch stimulation at
1 Hz.
The number of evoked post-tetanic twitches
detected is called the post-tetanic count (PTC).
PTC is a prejunctional event, the response can
vary with the nondepolarising muscle relaxant
used.
A PTC of 8 to 9 indicated imminent return of
TOF.

25. Pattern of electrical stimulation and evoked muscle responses to train-of-
four (TOF) nerve stimulation, 50-Hz tetanic nerve stimulation for 5
seconds (TE), and 1.0-Hz post-tetanic twitch stimulation (PTS) during four
different levels of nondepolarizing neuromuscular blockade

26. • 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
• Return of 1st
response to TOF related to PTC

27. APPLICATION OFPTC
• The PTC method is mainly used to assess the
degree of neuromuscular blockade when there
is no reaction to single-twitch or TOF nerve
stimulation, as may be the case after injection
of a large dose of a nondepolarizing
neuromuscular blocking drug.
• Used during surgery where sudden movement
must be eliminated(e.g., ophthalmic surgery)

28. Double-burst stimulation
(DBS)
• TOF ratio of less than 0.2 to 0.3 is difficult to
detect even by trained observers.
• To improve the detection rate, a new mode of
stimulation which consist of two short tetani,
separated by a interval long enough to allow
relaxation, evaluating the ratio of second to first
response has been proposed.
• DBS consist of two train of three impulses at
50Hz tetanic stimulation separated by 750msec

29. • 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
• However, absence of fade by tactile evaluation
to DBS does not exclude residual NM
Blockade

30. Pattern of electrical stimulation and evoked muscle responses to train-of-
four (TOF) nerve stimulation and double-burst nerve stimulation

32. Sites of nerve stimulation
• Ulnar nerve is most commonly used for NM
monitoring
• Adductor pollicis muscle is a useful clinical tool
because of its accessibility for visual, tactile &
mechanographic assessment is very good.
• Diaphragm is most resistant of all muscles &
requires 1.4-2times as much MR as adductor pollicis
• Other sites
• Facial nerve - orbicularis oculi
• Posterior tibial nerve - flexion of great toe

33. Relative sensitivities of muscle groups
to non depolarizing muscle relaxants

34. • In clinical anesthesia, the ulnar
nerve is the most popular site
• The distal electrode should be
placed about 1 cm proximal to the
point at which the proximal flexion
crease of the wrist crosses the
radial side of the tendon to the
flexor carpi ulnaris muscle.
• The proximal electrode should
preferably be placed so that the
distance between the centers of the
two electrodes is 3 to 6 cm

35. Electrode placement for
stimulation of the ulnar nerve
and for recording of the
compound action potential
from three sites of the hand.
A, Abductor digiti minimi
muscle (in the hypothenar
eminence).
B, Adductor pollicis muscle
(in the thenar eminence).
C, First dorsal interosseus
muscle

36. Recording of Evoked Responses
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]).

37. 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
• A preload of 200-300gm can be used to
align contractile elements

39. Electromyography
• It records the compound muscle action
potential (it is cumulative electrical signal
generated by individual APs of individual
muscle fibers)
• EMG records the compound MAP via
recording electrodes
• The amplitude of compound MAP is
proportional to number of muscle units that
generate MAP

40. Electrosensors

41. 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
• This is a nonisometric measurement & no
preload is necessary

42. 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

43. Piezoelectric Neuromuscular Monitors

44. Phonomyography
• Contraction of skeletal muscle generates
intrinsic low frequency sounds
• This low frequency sounds can be recorded
with special microphones
• Good correlation exists between PMG &
EMG,MMG,AMG

45. Evaluation of recorded evoked
responses
• Non-depolarizing NM Blockade
• Intense NM Blockade
• Deep NM Blockade
• Moderate or Surgical blockade
• Recovery
• Depolarizing NM Blockade
• Phase I blockade
• Phase II blockade

46. Levels of block after a normal intubating dose of a nondepolarizing
neuromuscular blocking agent (NMBA) as classified by post-tetanic count
(PTC) and train-of-four (TOF) stimulation.

47. Non-depolarising blockade
• Intense NM Blockade
• Intense neuromuscular blockade occurs within 3 to
6 minutes of injection of an intubating dose of a
non depolarizing muscle relaxant, depending on
the drug and the dose given.
• 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
•

48. • Surgical blockade
• Begins when the 1st
response to TOF stimulation
appears
• Presence of 1 or 2 responses to TOF indicates
sufficient relaxation
• This phase is characterized by a gradual return of
the four responses to TOF stimulation
• The presence of one or two responses in the TOF
pattern normally indicates sufficient relaxation for
most surgical procedures.

49. • When only one response is detectable, the degree
of neuromuscular blockade is 90% to 95%.
• When the fourth response reappears,
neuromuscular blockade is usually 60% to 85%
• Antagonism of neuromuscular blockade with a
cholinesterase inhibitor should not normally be
attempted when the blockade is intense or deep
because reversal will often be inadequate,
regardless of the dose of antagonist administered

50. • Recovery
• Return of 4th
response to TOF heralds recovery
phase
• 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

51. • When the TOF ratio is 0.4 or less, the patient
is generally unable to lift the head or arm.Tidal
volume may be normal, but vital capacity and
inspiratory force will be reduced.
• When the ratio is 0.6, most patients are able to
lift their head for 3 seconds, open their eyes
widely, and stick out their tongue, but vital
capacity and inspiratory force are often still
reduced.

52. • At a TOF ratio of 0.7 to 0.75, the patient can
normally cough sufficiently and lift the head for at
least 5 seconds, but grip and higher, vital capacity
and inspiratory force are normal.The patient may,
however, still have diplopia and facial weakness
• In clinical anesthesia, the TOF ratio, whether
recorded mechanically or by EMG, must exceed 0.80
or even 0.90 to exclude clinically important residual
neuromuscular blockade.

53. Depolarising NMblockade
• 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

54. Difference between
depolarising and non
depolarising block
DEPOLARISING BLOCK NON-DEPOLARISING BLOCK
Fasiculation No fasiculation
No tetanic fade Tetanic fade
No post-tetanic potentiation Post-tetanic facilitation
Potentiated by anticholinesterases Antagonised by anticholinesterases
Antagonism by non-depolarisers Potentiation by non-depolarisers
Potentiation by other depolarisers Antagonism by other depolarisers
May develop Phase 2 block No change in character of block

55. Clinical Vs TOFevoked
stimulation

56. Clinical vs TOFevoked stimulation

57. Clinical tests of Postoperative Neuromuscular
Recovery

58. Clinical application
To differentiate depolarising block and Non-depolarising
block
To see efficacy of depolarising block after administration
of drug and to judge whether the patient is fully relaxed
To see whether the pt is out of effect of block of
depolarising muscle relaxed
As a guide to administer first dose of non-depolarising
muscle relaxant
As a guide to see whether completeness of non-
depolarising neuromuscular block

59. As a guide to for starting of reversal of non-depolarising
block
To see a completeness of recovery
As a guide for incremental doses administration of non-
depolarising muscle relaxant
To differentiate respiratory paralysis i.e. central or
peripheral due to neuro muscular block
To diagnose overdose of sedatives cerebral depressants or
muscle relaxants

60. To diagnose phase II block after suxamethonium
To diagnose various neuromuscular disorders
To diagnose site of nerve injury
To diagnose electrolyte imbalance or disturbances
affecting NM Transmission
As a guide in diagnosis of prolonged apnea or recovery
after balanced anaesthesia

61. 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

62. Limitations of NMMonitoring
• 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

63. References
1. Millers text book of anesthesia,7th
ed.
2. Morgan`s principles of anesthesia