Neuromuscular monitoring

1. Neuromuscular monitoring
Dr Sumanth Gutta, Consultant Anaesthetist, Yashoda Hospitals, Hitech

2. Why?
1. Exclude clinically significant residual neuromuscular block after
administration of reversal
2. To monitor depth of neuromuscular block - complete relaxation
in robotic surgeries (Diaphragm and laryngeal adductors most
resistant)
3. Neuromuscular blocking drug, Reversal - appropriate dosing
• Risks of residual neuromuscular blockade
• Functional impairment of pharyngeal and upper esophageal
muscles. Most sensitive
• As a result, inability to maintain upper airway
• Hypoxemic events, Blurry vision, Patient distress

3. Why?

4. Why?

5. Guidelines

6. Guidelines

7. Guidelines

9. Levels of block

10. How to monitor
1. Clinical
• Tongue protrusion
• Head lift 5 seconds
• Hand grip
• Tidal volumes
2. Objective – quantification with a value

11. Objective Monitoring

12. Monitoring sites
• Ulnar nerve most common site
• Pulse oximeter to be measured from
different arm / leg
• AV fitula is no contraindication
• Motor neuron lesions will give false
readings

13. Monitoring sites

14. Monitoring sites

15. Electrodes
• Placed along a nerve transcutaneously
with surface electrodes
• Large conducting area makes difficult to
obtain supramaximal stimulation
• Polarity - Positive white/red, Negative
black
• Negative electrode over most superficial
part of the nerve being stimulated
• Positive electrode along course of the
nerve proximally

16. Equipment
• Current
• Current, not voltage. Change of
current with regard to skin
resistance
• Supramaximal stimulus. ~50mA.
Higher in those with edema
• Frequency
• One Hz is 1 stimulus per second
• Duration
• In milliseconds

17. Methods of detection
• Visual
• Tactile

18. Methods of recording
• Mechanomyography - Measures muscle contraction using a force transducer
• Kinemyography - Assesses APM contraction by measuring the degree of bending
of a sensor placed between the thumb and the first finger
• Electromyography - Detects compound muscle action potentials at the
neuromuscular junction
• Acceleromyography - Based on Newton’s Second Law of Motion (i.e., force = mass
x acceleration). AMG utilizes a piezoelectric sensor to measure tissue acceleration
with muscle contraction

19. Methods of recording

20. Methods of recording
• Electromyography Mechanomyography

21. Nerve Stimulation Patterns
• Single twitch
• Delivered at a frequency of 0.1 or 1 Hz. Control response strength is noted
• Strengths of subsequent twitches are then compared with the control and
expressed as a percentage of the control
• With both a nondepolarizing block and a depolarizing block, there will be a
progressively depressed response as the block develops

22. 1. Single twitch
• Single twitch stimulus is useful to establish a supramaximal stimulus and to
identify whether conditions satisfactory for intubation have been achieved
• It can be used (in conjunction with PTC) to monitor deep levels of NMB
• Disadvantages
• Control needed
• Cannot distinguish between depolarizing and nondepolarizing block
• Lower body temperature will cause a reduced response

23. 2. Train of Four

24. 2. Train of Four

25. 2. Train of Four
• Four single pulses of equal intensity delivered at intervals of 0.5 seconds
• TOF should not be repeated more frequently than every 12 seconds
• Before any relaxant has been given, all four responses are the same
• Pattern with depolarizing block differs from non-depolarizing block
• Nondepolarizing block - Progressive depression of height with each twitch (fade)
• As the block is deepened - the fourth twitch will be eliminated, then the third…

26. 2. Train of Four

27. 2. Train of Four

28. 2. Train of Four

29. 3. Tetanus
• Rapidly repeated (50 or 100 Hz) stimulus.
More the frequency, more sensitive
• No NMB - causes sustained stimulated muscle
contraction
• Depolarizing block - response will be
depressed in amplitude
• Nondepolarizing block – response is
depressed in amplitude, contraction not
sustained (fade)

30. 3. Tetanus
• Duration is important because it affects fade. Standard is 5 seconds
• Should not be repeated more often than every 5 minutes
• Tetanic stimulation is very painful. Avoided in conscious patient

31. 4. PTC
• Post-tetanic facilitation (potentiation, PTF) - temporary
increase in response to stimulation following a tetanic
stimulus. Seen with nondepolarizing block
• When NMB is deep (no response in TOF) - possible to
estimate NMB by using PTC
• PTC - Tetanic stimulus of 50 Hz for 5 seconds. 3-second
pause. Single-twitch stimuli at 1 Hz. Number of post-
tetanic responses is counted
• PTC of 12–15 suggests that the return of a TOF twitch is
imminent
Suggamadex 2mg/kg can be
administered at PTC of 1-2

32. 4. PTC

33. Rocuronium recovery chart

34. 5. Double-Burst Stimulation
• Two short bursts of 50-Hz separated by 0.75 seconds. Interval 12 seconds
• 90 seconds gap needed when switching between DBS and TOF stimulation
• DBS used to detect residual NMB
• Also used to assess deep block since the first twitch in double burst can be
detected at deeper block levels than the first twitch in TOF
• DBS causes more discomfort than TOF stimulation but less than tetanic
stimulation

35. 5. Double-Burst Stimulation

36. Problems
• Patient discomfort – Tetanic, DBS
• Electrical interference – ECG trace, Pacemaker
• Low batteries going unchecked

37. Best Used

38. Suggested Evidence-Based Practices
• Use muscle relaxants only when necessary
• Minimum degree of recovery should be a TOF Count of 4 prior to
anticholinesterase reversal
• Use of anticholinesterases in fully recovered patients may induce weakness of
airway muscles
• If TOF ratio is <0.40, use reversal
• If TOF ratio is between 0.40 and 0.90, consider low-dose reversal (50%)
• If TOF ratio is >0.90, no reversal is recommended

40. Practical Conditions where NMM is essential
• Infusions of neuromuscular blocking drugs, Long-acting drugs are used, Surgery is
prolonged
• Inadequate reversal may have devastating effects - severe respiratory disease,
morbid obesity
• Liver or renal dysfunction, when pharmacokinetics are altered
• Myasthenia gravis or Eaton–Lambert syndrome

41. Is it needed?

42. Further Reading

43. Thank You