This document discusses neuromuscular monitoring during anesthesia. It introduces the history and objectives of neuromuscular monitoring, and describes different techniques used including train of four (TOF), single twitch, tetanic and post-tetanic count stimulation. Sites for nerve stimulation like the ulnar nerve are outlined. Factors influencing neuromuscular blockade like prolonged infusions are discussed. The document emphasizes the importance of monitoring to avoid residual paralysis.

1. NEUROMUSCULAR
MONITORING
DR T. MASIYIWA

2. INTRODUCTION
• In the mid 1950s inadequate recovery of neuromuscular function at
the end of surgery was a common occurrence
• In 1958 Christie and Churchill-Davison described how nerve
stimulators could be used to assess neuromuscular function
objectively during anesthesia and how diagnosis of prolonged apnea
could be made after the use of neuromuscular blockers.
• In 1965 Churchill Davison stated that “the only satisfactory method of
determining the degree of neuromuscular block is to evaluate motor
nerve with an electric current and observe the contraction of the
muscles innervated by that nerve”

3. INTRODUCTION
• In awake patients muscle power can be evaluated through tests of
voluntary muscle strength.
• During anesthesia and recovery from anesthesia this is not possible.
Instead the clinician uses clinical tests to assess muscle power directly
and to estimate neuromuscular function indirectly (muscle tone , the
feel of anesthesia bag, an indirect measure of pulmonary compliance,
tidal volume and inspiratory force).
• Whenever precise information regarding the status of neuromuscular
functioning is desired the response of muscle to nerve stimulation
should be assessed.

4. OBJECTIVES OF NEUROMUSCULAR
MONITORING
• TO DETERMINE THE ONSET OF NEUROMUSCULAR BLOCKADE
• TO DETERMINE LEVEL OF MUSCLE RELAXATION DURING SURGERY
• TO ASSESS PATIENTS RECOVERY FROM BLOCKADE TO MINIMIZE RISK
OF RESIDUAL PARALYSIS

5. WHY DO WE MONITOR
RESIDUAL POSP-OP NEUROMUSCULAR BLOCKADE
• Functional impairment of pharyngeal and upper esophageal muscles
• Impaired ability to maintain the airway
• Increased risk for post op pulmonary complications
• Decreased chemoreceptor sensitivity to hypoxia
• Difficult to exclude clinically significant residual curazation by clinical
evaluation

6. THE DIAPHRAGM
• The diaphragm is among the most resistant of all muscles to both
depolarizing and non depolarizing neuromuscular blocking drugs.
• It 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.

7. THE DIAPHRAGM

8. CONDITIONS WHERE NEUROMUSCULAR
MONITORING IS ESSENTIAL
• after prolonged infusions of neuromuscular blocking drugs or when long acting
drugs are used.
• When surgery or anesthesia is prolonged
• When inadequate reversal may have devastating effects, for example severe
respiratory disease, morbid obesity.
• In conditions where administration of a reversal agent may cause harm e.g.
tachyarrhythmias, cardiac failure
• Liver or renal dysfunction when pharmacokinetics of muscular relaxants may be
altered
• Neuromuscular disorders such as myasthenia gravis or Eaton-Lambert syndrome
• Surgeries requiring profound neuromuscular blockade e.g. neurosurgery, vascular
surgery in vital areas like thoracic cavity

9. TYPES OF PERIPHERAL NERVE STIMULATION
• Neuromuscular function is monitored by evaluating the muscular
response to supramaximal stimulation of a peripheral motor nerve
• Two types of stimulation can be used –electrical (most commonly
used) and magnetic
• Magnetic nerve stimulation has several advantages over electrical
stimulation. It 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 stimulation and it is difficult to achieve
supramaximal stimulation with this method

10. PRINCIPLES OF PERIPHERAL NERVE
STIMULATION
• The reaction of a single muscle fiber to a stimulus follows an all or
none pattern
• Response 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 agent the response
of the muscle decreases in parallel with the number of fibers blocked
• Reduction in response during constant stimulation reflects degree of
NM blockade.

11. ESSENTIAL FEATURES OF ELECTRICAL IMPULSE
• square waveform-The impulse should be monophasic and rectangular i.e.
it should be a square waveform because a biphasic impulse may cause
repetitive firing (a burst of action potentials in the nerve) thus increasing
the response to the stimulation.
• Nerve stimulators are constant and variable voltage delivery devices. They
are battery powered and have digital display of delivered current. They also
have audible signal on delivery of stimulus and have audible alarm for poor
electrode contact.
• Nerve stimulation should have many patterns of stimulation
• duration of impulse-optimal duration is 0.2 to 0.3 msec. A pulse exceeding
0.5msec may stimulate the muscle directly or cause repetitive firing

12. ESSENTIAL FEATURES OF ELECTRICAL IMPULSE
• Threshold stimulus-It is the current amplitude in milliamperes
required to depolarize the most sensitive fibers in a given bundle to
elicit a detectable muscle response
• Maximal stimulus-current which generate response in all fibers
• Supramaximal stimulus-it is approximately 20-25% higher intensity
than the current required to depolarize all fibers in a particular nerve
bundle. This is generally attained at current intensity 2-3 times higher
than threshold current.
• Submaximal stimulus-a current intensity that induces firing of only a
fraction fibers in a given nerve bundle. A potential advantage of
submaximal is that it is less painful than supramaximal current

13. ESSENTIAL FEATURES OF ELECTRICAL IMPULSE
• Stimulus frequency-the rate(Hz) at which each impulse is repeated in
cycles per second
• Current intensity-it is the amperage of the current delivered by the
nerve stimulator.(0-80mA). The intensity reaching the nerve is
determined by the voltage generated by the stimulator and
impedance of the electrode, skin and underlying tissues.
• Reduction of temperature increases the tissue resistance(increased
impedance) and may cause reduction in the current delivered to fall
below the supramaximal level.

14. EQUIPMENT
•The neuromuscular monitoring equipment consists of:
A)NERVE STIMULATOR
B)STIMULATING ELECTRODES

15. The ideal nerve stimulator should have other
features as well:
• The polarity of the electrodes should be indicated and the apparatus
should be capable of delivering the following modes of stimulation:
✓TOF (as both a single train and in a repetitive mode, with TOF
stimulation being given every 10 to 20 seconds)
✓Single twitch stimulation
✓Tetanic stimulation at 50Hz
✓Post tetanic count
✓If the nerve stimulator does not allow objective measurement of the
response to TOF stimulation, at least one DBS mode should be
available preferably DBS3.3

16. TYPES OF ELECTRODES
SURFACE ELECTRODES
• Pre-gelled 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)
• With careful skin preparation the threshold for twitch is generally
<15mA

17. TYPES OF ELECTRODES
NEEDLE ELECTRODES
• Subcutaneous needles deliver impulse near the nerve
• Require less current
• Useful when supramaximal stimulation cannot be achieved using
surface electrodes which usually occurs when the skin is thickened,
cold, or edematous and in obese, hypothyroid, diabetic or renal
failure patients.
• They are effective because they bypass the tissue impedance

18. POLARITY
• stimulators produce a direct current by using one negative and one
positive electrode
• Should be indicated on the stimulator
• Maximal effects 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 muscle stimulation

19. SITES USED FOR NEUROMUSCULAR
MONITORING
ULNAR NERVE(MOST COMMON SITE)
• Place negative electrode (black) on wrist line with the smallest digit 1-
2cm below skin crease.
• Positive electrode (red) 2-3cm proximal to the negative electrode
• RESPONSE-Adductor pollicis muscle
thumb adduction

20. SITES USED FOR NEUROMUSCULAR
MONITORING
FACIAL NERVE
Place negative electrode (black) by ear lobe and the positive (red) 2cms
from the eyebrow (along facial nerve inferior and lateral to the eye)
Response-Orbucularis occuli muscle (eye lid twitching)

21. SITES USED FOR NEUROMUSCULAR
MONITORING
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)

22. PATTERNS OF NERVE STIMULATION
• SINGLE TWITCH STIMULATION
• TOF (TRAIN OF FOUR)
• TETANIC STIMULATION
• POST TETANIC COUNT (PTC)
• DOUBLE BURST STIMULATION(DBS)

23. SINGLE TWITCH STIMULATION
• A Single supramaximal electrical stimuli is applied to a peripheral
motor nerve at frequencies ranging from 1.0Hz (once every second)
to 0.1 Hz (once every 10 seconds)
• Height of response depends on the number of unblocked junctions.
• the response to single twitch stimulation depends on the frequency
at which the individual stimuli are applied
• Because 1 Hz stimulation shortens the time necessary to determine
supramaximal stimulation this frequent is sometimes used during
induction of anesthesia

24. SINGLE TWITCH STIMULATION
• Pre relaxant control response is noted and compared with
subsequent responses
• Responses will only be depressed when NM blocker occupies 75% of
receptors
• Used to assess potency of drugs and is also useful to determine onset
of NM block
• In both depolarizing and non depolarizing blocks there is progressive
decrease in twitch height so cant differentiate between the two.

25. SINGLE TWITCH STIMULATION

26. INTERPRETATION

27. SINGLE TWITCH STIMULATION
ADVANTAGES
• Useful in establishing a supramaximal stimulus and for identifying when
conditions satisfactory for intubation have been achieved
• Can be used in conjunction with tetanic stimulus to monitor deep levels of
Neuromuscular blockade.
DISADVANTAGES
• Cannot differentiate depolarizing and non depolarizing neuromuscular
blockade
• Requires standardization and calibration of the ST amplitude
• The response’s return to control level does not guarantee that full recovery
from neuromuscular blockade occurred

28. TRAIN OF FOUR
• Train of four nerve stimulation was introduced by Ali and Associates
during the early 1970s
• It consists of four supramaximal stimuli being given every 0.5 seconds
(2Hz)
• When used continuously each set (train) of stimuli is normally
repeated every 10th and 20th second
• Each stimulus in the train causes the muscle to contract and fade in
response and provides the basis for evaluation
• The Train Of Four ratio (TOFR) is the ratio of the amplitude of the
fourth to that of the first, expressed as percentage or fraction.(T4/T1)

29. TRAIN OF FOUR
• In the control response( the response obtained before the
administration of a muscle relaxant, all four responses are ideally the
same: the TOF ratio is 1.0
• During a partial nondepolarizing block the T4/T1 ratio
decreases(fades) and is inversely proportional to the degree of block
• During a partial depolarizing block, reduction in twitch height occurs,
ideally the TOF ratio is approximately 1.0
• Fade, in the TOF response after injection of succinylcholine signifies
development of phase II block.

30. TRAIN OF FOUR

31. TRAIN OF FOUR

32. TRAIN OF FOUR

33. TRAIN OF FOUR

34. TRAIN OF FOUR COUNT
• The TOF count is defined as the number as the number of evoked
responses that can be detected.
• It permits quantitative assessment of
non depolarizing block
• With recovery or reversal of a non
depolarizing block, the train of four count
increase until there are four responses,
then fade increases

35. TRAIN OF FOUR COUNT AND PHYSIOLOGICAL
CORRELATION
% OF MUSCLE BLOCKADE

36. TRAIN OF FOUR ADVANTAGES
• 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.
• Can distinguish between depolarizing and non depolarizing block
• Is it of value in detecting and following of a phase II block after
succinylcholine administration
• It is less painful and unlike tetanic stimulation does not generally influence
subsequent monitoring of the degree of neuromuscular block

37. TRAIN OF FOUR DISADVANTAGES
• Poor performance at both extremes of NMB, deep relaxation or near
complete recovery
• Tactile observation or visual observation of TOFR is of little value above a ratio
of 0.4-0.5

38. TETANIC STIMULATION
• Tetanic stimulation consists of very rapid (e.g. 30,50 or 100Hz)
delivery of electrical stimuli
• The most commonly used pattern in clinical practice is 50Hz
stimulation given for 5 seconds although some investigators have
advocated the use of 50, 100 and 200 Hz stimulation for 1 second
• During normal neuromuscular transmission and a pure depolarizing
block, the muscle response to 50 Hz tetanic stimulation for 5 seconds
is sustained .

39. TETANIC STIMULATION
• during a non depolarizing block and a phase ii block after the
injection of succinylcholine the response will not be sustained (i.e
fade occurs)
• fade in response to tetanic stimulation is normally considered a
presynaptic event, the traditional explanation is that at the start of
tetanic stimulation, large amounts of acetylcholine are released from
immediately available stores in the nerve terminal
• as these stores become depleted the rate of acetylcholine release
decreases until equilibrium between mobilization and synthesis of
acetylcholine is achieved

40. TETANIC STIMULATION
• when the “margin of safety” at the postsynaptic membrane (the
number of free cholinergic receptors) is reduced by non depolarizing
neuromuscular blocking drugs, a typical reduction in twitch is seen
with a fade during, for instance, repetitive stimulation
• In addition to this postsynaptic block, non depolarizing
neuromuscular blocking drugs may also block presynaptic neuronal-
type acetylcholine receptors thereby leading to impaired mobilization
of acetylcholine within the nerve terminal. This effect substantially
contributes to the fade in the response to tetanic (and TOF)
stimulation.

41. TETANIC STIMULATION

42. TETANIC 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
• This is because the increase in mobilization and synthesis of Ach
continues for sometime after discontinuation of the stimulus
• Tetanic stimulation is extremely painful which limits its use in
unanesthetized patients and it is visually and tactically unpredictable.

43. POST TETANIC COUNT STIMULATION
• During intense block no response to TOF and single twitch stimulation
occurs
• Therefore these modes of stimulation cannot be used to determine
the degree of blockade
• It is possible however to quantify intense neuromuscular blockade of
the peripheral muscles by applying tetanic stimulation (50Hz for 5
seconds) and observing the post-tetanic response to single twitch
stimulation given at 1Hz starting 3 seconds after the end of tetanic
stimulation.

44. POST TETANIC COUNT STIMULATION
• As the intense block dissipates, more and more responses to
POSTTETANIC TWITCH STIMULATION appear.
• For a given neuromuscular blocking drug, the time until return of the
first response to TOF stimulation is related to the number of post-
tetanic twitch responses present at a given time (i.e., POST TETANIC
COUNT).

45. POST TETANIC COUNT STIMULATION

46. DOUBLE-BURST STIMULATION
• Double burst stimulation has been introduced as an alternative to
TOF stimulation in an attempt to improve the ability to detect residual
neuromuscular blockade by subjective means
• DBS consists of two short bursts of 50Hz tetanic stimulation
separated by 750msec
• The duration of each square wave impulse in the burst is 0.2 msec
• The two commonly used patterns are DBS3,3 and DBS 3,2

47. DOUBLE-BURST STIMULATION
• The pattern DBS3,3 consists of a mini tetanic sequence of three
stimuli at 50Hz followed 750msec later by an identical sequence
• The pattern DBS3,2 consists of brief three 50Hz stimuli, followed
750msec later by two short 50Hz stimuli
• In non paralyzed muscle, the response to DBS3,3 is two short
contractions of equal strength
• In a partly paralyzed muscle the second response is weaker than the
first i.e. the response fades

48. DOUBLE-BURST STIMULATION

49. NON DEPOLARIZING BLOCKADE
• Intense NM blockade-this phase is called “period of no response”
• Deep NM blockade-deep blockade 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

50. NON DEPOLARIZING BLOCKADE
• Recovery- return of 4th response on TOF heralds recovery phase
• NB PRESENCE OF SPONTANEOUS RESPIRATION IS NOT A SIGN OF
RECOVERY
• Adequate neuromuscular recovery- TOFR >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. METHODS FOR EVALUATING EVOKED
RESPONSES
A) VISUAL ASSESSMENT
• Can be used to count number of responses present with a TOF
stimulus to determine the PTC and to detect the presence of fade
with TOF or DBS
• The observer should be at an angle of 90 degrees to the motion
• It is difficult to determine the TOFR or to compare a single twitch
height to its control visually
• Visually assessing fade with tetanic stimulus or DBS appears to be
fairly accurate

52. TACTILE ASSESSMENT
• Accomplished by placing the evaluators fingertips lightly over the
muscle to be stimulated and feeling the strength of contraction
• More sensitive than visual assessment
• Can be used to evaluate the presence or absence of responses and/or
fade with TOF, DBS, Tetanic stimulation
• However it is difficult for trained observers to detect TOF fade
manually unless the TOFR is below 40%

54. •OBJECTIVE ASSESSMENT

55. ACCELEROMYOGRAPH (NON ISOMETRIC)
• This technique uses a miniature piezoelectric transducer to determine the
rate of angular acceleration.
• Newton’s second law F=ma
• 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
introduced with an output voltage proportional to the deformation of the
crystal.
• This is an isometric measurement and there are less stringent
requirements for immobilization of the arm, fingers and thumb and also
preload is necessary

56. ACCELEROMYOGRAPH (NON ISOMETRIC)

57. 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 mechanomyogram MMG
• 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.

59. 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 compound action potential is a high speed event that for many
years could be picked up only by means of a preamplifier and a
storage oscilloscope
• The evoked EMG response is most often obtained from muscles
innervated by the ulnar or median nerves.

61. USES OF NERVE STIMULATORS IN DAILY
CLINICAL PRACTICE
• During induction
• During Surgery
• During reversal of Neuromuscular Block
• Postoperative period
• Long term muscle relaxant infusions
• Nerve location

62. COMPLICATIONS OF NEUROMUSCULAR
MONITORING
• Underestimating the extent of blockade
• Unable to elicit a twitch by electrical stimulation
• Chemical burn from electrolysis caused by direct current via surface
electrodes
• Burn with needle electrodes
• Pacemaker suppression with a nerve stimulator

63. CLINICAL TESTS OF POSTOPERATIVE
NEUROMUSCULAR RECOVERY
MOST REALIABLE
• Sustained head lift for 5 seconds
• Sustained leg lift for 5 seconds
• Sustained handgrip for 5 seconds
• Sustained “tongue depressor test”
• Maximum inspiratory pressure 40 to 50 cm H20 or greater

64. CLINICAL TESTS OF POSTOPERATIVE
NEUROMUSCULAR RECOVERY
UNRELIABLE
• Sustained eye opening
• Protrusion of the tongue
• Arm lift of the opposite shoulder
• Normal tidal volume
• Normal or nearly normal vital capacity
• Maximum inspiratory pressure less than 40 to 50 cm H20

65. References
• Morgan and Mikhail’s Clinical Anaesthesiology Sixth Edition
• Oxford Handbook Of Anaesthesia Third Edition
• Lake CL, Hines RL, Blitt CD. Clinical monitoring: Practical implications
for anesthesia and critical care 2011
• Stoelting RK, Miller RD. Basics of anesthesia Fourth Edition

66. •THANK YOU