neuromuscular monitoring by dr. ahmed mostafa assist. prof. of anesthesia and i.c.u

Neuromuscula

r monitoringBy

Dr. Ahmed MostafaAssist. prof. of anesthesia and

I.C.U.

Value of neuromuscular blocking drugs

- Facilitate endotracheal intubation. - Provide optimum surgical conditions for a

variety of procedures.- Significantly reduces the concentration of

volatile anesthetics required to provide adequate analgesia and amnesia with rapid postoperative recovery.

Value of monitoring neuromuscular blockade

Titration of NMBD doses to the desired level of paralysis.

Detection of unusual sensitivity, resistance, or altered

clearance of a relaxant in the course of the anesthetic.

Evaluation of whether neuromuscular blockade can be

pharmacologically reversed.

Assessment of the adequacy of reversal to assure that residual

neuro-muscular blockade is not present.

Clinical monitoring

Ability to cough and swallow.

Sustained eye opening for at least 5 seconds

without diplopia.

Sustained head or leg left for at least 5 seconds

without support.

Sustained protrusion of the tongue without fade.

Sustained forceful hand grip without fade.

Clinical monitoring

Ability to resist removal of a tongue blade from

clenched teeth.

Tests assessed In unconscious patients:

- Inspiratory force to produce 25 Cm H2O.

- Vital capacity.

- Tidal volume.

Peripheral nerve stimulation

Standard electrical pulse:

Current amplitude: Supra maximal stimulus (50 mA) is applied:

The strength of the stimulus is increased until the response no longer

increases. Then it is increased by further 25%. This is to ensure

consistent excitation of all muscle fibers.

Stimulus shape: Monophasic and rectangular (Square wave pattern)

Stimulus duration: 0.2 msec.


Patterns of Stimulation:

1. Single-twitch stimulus:

Frequency: 0.1 Hz.

(one stimulus every10 s).



2. TOF (Train of four) stimulation:




- It is the most commonly used stimulus. Each train consists of four stimuli

at 2 Hz (four stimuli in 2 seconds) that are again repeated every 10

seconds.

- In the absence of neuromuscular blockade, the TOF will evoke four

twitches of equal strength ( TOF ratio = 1).

- In depolarizing neuromuscular blockade, the TOF will evoke four twitches

of equal strength but decreased in height ( TOF ratio = 1).




- In non-depolarizing neuromuscular blockade: fade

o First, with the onset of neuromuscular blockade, the amplitude of the

fourth twitch (T4) will decrease with successive stimuli.

o Second, within each TOF, there is a clear decrement between T4and T1.

The T4/T1 ratio can be easily compared if objectively measured.




In clinical practice, when the strength of the first twitch is

reduced to 75% of the maximal height, only three twitches

will be demonstrable. With increased neuromuscular

blockade to a T1of 20%, two twitches will be observed. At

90% suppression of T1; only one twitch will be perceptible.




These patterns are reversed as muscle activity returns.

Initial studies demonstrated that at T4/T1 = 0.75,

awake patients can sustain a 5-second head lift,

generate a vital capacity of 15–20 mL/kg with an

inspiratory force of –25 cm H2O,and cough effectively.



3. Tetanic stimulation:

• 50 Hz for 5 s produces detectable fade in muscle contraction,

the extent of which is related to neuromuscular block.

• It is intolerable and painful in awake patients so, it is used

only in anesthetized patients.



3. Tetanic stimulation:



4. Post-tetanic facilitation:

Tetanic stimulation for 5 s. Subsequent 1 Hz twitch

stimulation can overcome the high concentrations of

NMBAs. The number of twitches generated (i.e. the post-

tetanic count) reflects the degree of neuromuscular

blockade.



4. Post-tetanic facilitation:



5. Double-burst stimulation (DBS):

- consists of two short bursts of three stimuli at 50 Hz

separated by 750 msec.

- The responses to each burst are close enough to be palpated

as a strong single muscle contraction.




- Any fade that is manifested with a partial blockade may be easier to

detect between the sets of stimuli with DBS than with TOF.

- In the absence of fade to DBS, there is a 90% chance that TOF is

≥0.6 and a 75% chance that TOF is <0.6 when fade is present.

Methods used to quantify muscle responses

Visual observation and palpation:

The easiest but least accurate

Electromyography:

uses electrodes to record the compound muscle

potential stimulated by the PNS.

The ulnar nerve is used.


Acceleromyography:

Acceleration of a distal digit is directly proportional to

the force of muscle contraction and therefore inversely

proportional to the degree of neuromuscular block.

The transducer uses a piezoelectric crystal secured to

the distal part of the digit measured and the PNS

provides the electrical stimulus.


Mechanomyography:

Uses a strain gauge to measure the tension generated

in a muscle.

The tension produced on PNS stimulation is

converted into an electrical signal.

Mechanomyography is generally used for research.

Thank youDr.

Ahmed Mostafa

neuromuscular monitoring by dr. ahmed mostafa assist. prof. of anesthesia and i.c.u

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