Basics of Neuromuscular monitoring during anaesthesia.

1. Neuromuscular Monitoring
DR. LIAQAT ALI
DR. S. A. FATIMA

2. Goals
 Principles
 Types of neuromuscular monitoring
 Definitions
 Sites of nerve stimulation and responses
 Patterns
 Clinical practice

3. PRINCIPLES
 Supra-maximal stimulation: the electrical stimulus required to block all the
muscle fibers of a muscle which are supplied by a single nerve,is the maximum
stimulus. Supra-maximal stimulus is 15 to 20 percent greater than the maximal
stimulus.
 Calibration: It adjusts the gain f the device to ensure that the observed response is
within the measurement window of the device and is closest to 100% of control
response.
 Impedance: is the resistance offered by the skin to the passage of current. Value =
5 kilo ohms.
 Safety margins: neuromuscular block is evident only once 70% of the receptors
are blocked. So, this should be kept in mind 70 % of the receptors may still be
blocked and not detectable on the nerve stimulator.

4. Types of peripheral nerve stimulation
 Electrical
 Commonly used in clinical practice
 Easy to use
 painful
 Magnetic
 Not used clinically
 Bulky apparatus
 Not painful

5. Site of nerve stimulation selection
 The site should be easily accessible.
 Allow quantitative monitoring.
 Direct muscle stimulation should be avoided.
 Happens when electrodes are directly placed on the muscle being tested.
 To prevent this, the nerve-muscle unit should be chosen so that the site of nerve and site
of responding muscle are anatomically distinct.

6. Nerve-Muscle Units
 Ulnar nerve--adductor pollicis muscle.
 Easily accessible
 When arms are abducted and patient is supine.
 Nerve and muscle are topographically distinct.
 Adduction of the thumb.
 Facial Nerve--orbicularis oculi; Facial Nerve—Corrugator supercilli
 When arms are tucked under drapes.
 Risk of direct muscle stimulation is significant.
 Can be elicited with lower current i.e 23 to 30 mA.
 winking of eye and wrinkling of the brow respectively.

7. Nerve-Muscle Units
 Posterior Tibial Nerve—Flexor halluces brevis
 Easily accessible
 When hands are inaccessible.
 Nerve and muscle are topographically distinct.
 Flexion of big toe.

8. Electrodes and assembly
 Two types of electrodes are used:
needle
surface
 Surface electrode:
 pre-gelled silver or silver chloride
 Conduction area should be 7 to 11 mm
 Negative terminal is placed on nerve
 Positive terminal is placed proximally
 Space between the centre of two electrodes should be 3 to 6cm.

9. Electrodes and assembly contt.
 Needle electrodes
 Used when skin electrodes cannot be applied
 When the selected current cannot be delivered with surface electrodes
 Specially coated needles or ordinary injection needles can be used
 Sterile technique is mendatory
 Needle is placed subcutaneously to avoid direct injury to the nerve.

10. Patterns of Nerve Stimulation
 Single Twitch
 Train Of Four
 Train Of Four Ratio
 Double Burst
 Tetanic Stimulation
 Post-tetanic Count Stimulation

11. Single Twitch Stimulation
 Stimulation Pattern
 Single electrical stimulus is applied to the peripheral motor nerve.
 Frequency 1hz (once every sec) to 0.1Hz (one every 10 seconds).
 Clinical application
 Only pattern used to assess the neuromuscular block with depolarizing NMBA
succinylcholine.
 As a component of PTC stimulation.
 As 0.1 Hz single twitch stimulation, sometimes used in the clinical trials to see the onset
of neuromuscular blockade.

12. Single Twitch Stimulation

13. Train Of Four Stimulation
 Stimulation Pattern
 Consists of four supra-maximal stimuli given every 0.5sec (2Hz); and each stimulus in TOF
causes the muscle to contract.
 The response evaluation is based upon either of two:
 TOF Count: No. of discernible responses after TOF simulation i.e TOF Count.
 TOF Ratio: Fade in TOF responses i.e dividing the amplitude of fourth response to that of 1st
response.
1. Without NMBA: all four responses are same---TOF ratio is 1.
2. With Non-dep NMBA:TOF ratio decrease---fade occurs.
3. With Dep NMBA:No Fade occurs---TOF Ratio is 1. Phase 1 block.
4. Fade with dep NMBA: phase II block has occurred.

14. Train Of Four Stimulation

15. Train Of Four Stimulation
 Clinical Application
 TOF count:
 Onset of neuromuscular blockade
 Moderate block
 TOF Ratio
 Onset
 Surgical relaxation (maintenance).
 Recovery.
 Reversal.
 Extubation.
 Post-op residual neuromuscular blockade.

16. Train Of Four Stimulation
Advantages:
 Most frequently used.
 Less painful than DBS and PTC.
 Reliable for all phases of anesthesia(onset of neuromuscular blockade till recovery).
Limitations:
 Subjective assessment overestimates the neuromuscular recovery i,.e. TOF ratio 0.4 to 0.9 fade
cannot be detected either visually or tactically.
 TOF ratio does not allow the clinician to quantify intense and deep levelsof neuromuscular
blockade.
 Does not allow monitoring of depolarizing neuromuscular blockade.

17. Double-Burst Stimulation
 Stimulation Pattern:
 Two short burst of 50 Hz of tetanic stimulation separated by 750ms, with a 0.2 ms
duration of each square wave impulse in the burst.
 Modes of DBS: depend upon the no. of impulses in each burst.
 DBS 3,3 Mode: three impulses in each burst
 DBS3,2 Mode: 1st burst has 3impulses and second burst has 2 impulses.
 Each impulse is of 0.2 second regardless ofDBS mode.

18. Double-Burst Stimulation

19. Double-Burst Stimulation
 Response:
 The individual twitches in each burst are blended and felt to be single amplified muscle
contraction.
 The response is two short muscle contractions and fade in second burst compared to the
first burst is the basis for evaluation.

20. Double-Burst Stimulation
Clinical application
 Manual (tactile or visual) detection of block.
 Recovery
 Post-op residual block.
Advantages vs disadvantages:
 Better visal assessment cpmpared to TOF count.
 Objective monitoring is superior to DBS.
 DBS is painful as compared to TOF.

21. Tetanic Stimulation
 Stimulation Pattern
 High frequency delivery of electrical stimuli i.e. 50 Hz for 5 seconds or 100 Hz to 200 Hz
given for 1second.
 Response
 Without any NMBD: fade does not occur.
 With non-dep NMBD: fade occurs.
 With Dep NMBD: no fade.
 Fade with Dep NMBD: phase II block.

22. Tetanic Stimulation

23. Tetanic Stimulation
 Clinical Application:
 Used as a component of PTC.
 Limited use sue to being very painful.

24. Post Tetanic Count Stimulation
 Stimulation Pattern
 A composite stimulation pattern consisting of tetanic stimulation of 50 Hz for 5 seconds
followed by 10 t 15 single twitches given at 1 Hz starting at 3 seconds past the tetanic
stimulation.
 Clinical application
 When dense neuromuscular paralysis is required.
 Onset (deep paralysis—less than 3 post tetanic count.
 Surgical paralysis
 Recovery( although painful but ideal).

25. Post Tetanic Count Stimulation

26. Subjective monitor
 Peripheral nerve stimulator: only allows the stimulation of the target nerve;
subsequent muscular response is evaluated subjectively (tactilely or visually).

27. Objective Monitors
 Mechanomyography:
 Evoked mechanical response of the muscle.
 gold standard technique.
 Electromyography:
 Evoked electrical response of the muscle
 Oldest method
 Acceleromyography:
 Acceleration of musv;le response
 Based on newton’s second law i.e. Force= Mass X acceleration.
 Kinemyography:
 Evoked electrical response in a flexible piezoelectric film sensor attatched to the muscle.
 Cuff pressure modality:
 Measurement of pressure changes in BP Cuff after contaction of upper arm muscles.
 Compressomyography:
 measurement of a spherical balloon after hand contraction

28. Mechanomyography

29. Acceleromyography

30. Acceleromygraphy

31. Electromyography

32. Evaluation Of Recorded Evoked Responses with Non-
Depolarizing NMBA
 Intense Block
 Onset: within 3 to 6 minutes of intubating dose.
 Also called ‘period of no response’.
 Can only be antagonized by sugammadex high dose 16mg/kg.
 Deep block
 Intense block is followed by deep block.
 Absence of response to TOF but with 1 PTC.
 Assured by PTC less than and equal to 3 in laparoscopic surgeries.
 Can only be reversed by sugammadex moderate dose 4mg/kg.

33. Evaluation Of Recorded Evoked Responses with
Non-Depolarizing NMBA
 Moderate block
 Begins with first response to TOF and gradual return of four stiuli of TOF.
 When Ist TOF response reappears, degree of block is 90 to 95 %
 When fouryth response to TOF reappears, degree of block is 60 to 85%.
 Reversed with sugammadex low dose 2mg/kg.
 Or by neostigmine if TOF ratio 0.7 or above.
 Recovery from block
 Return of fourth response to TOF
 TOF ratio should be 0.9 with MMG or EMG and 1.0 with AMG to exclude residual blockade.

34. Evaluation Of Recorded Evoked Responses
with Depolarizing NMBA
 Phase I block
 Occurs in patients given succinylcholine once or with normal plasma pseudocholinesterase levels and
genetics.
 No fade
 No post tetanic facilitation
 TOF ratio 1.0
 TOF count is either 4 or 0.
 Phase II block
 Occures with repeated doses or continuous infusion of succinylcholinein patients with normal
pseudocholinesterase levels and normal genetics or patients with abormal plama pseudocholinesterase
levels or abnormal genetics.
 Fade occurs
 TOF ratio is utilized to differentiate the phase I and phase II blockade.

35. THANK YOU