Neuromuscular monitoring By Dr. Ahmed Mostafa Assist. 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 H 2 O. -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.

Peripheral nerve stimulation Patterns of Stimulation: 1.Single-twitch stimulus: Frequency: 0.1 Hz. (one stimulus every10 s).

Peripheral nerve stimulation Patterns of Stimulation: 2. TOF (Train of four) stimulation:

Peripheral nerve stimulation Patterns of Stimulation: 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).

Peripheral nerve stimulation Patterns of Stimulation: 2. TOF (Train of four) stimulation: -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.

Peripheral nerve stimulation Patterns of Stimulation: 2. TOF (Train of four) stimulation: 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.

Peripheral nerve stimulation Patterns of Stimulation: 2. TOF (Train of four) stimulation: 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.

Peripheral nerve stimulation Patterns of Stimulation: 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.

Peripheral nerve stimulation Patterns of Stimulation: 3. Tetanic stimulation:

Peripheral nerve stimulation Patterns of 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.

Peripheral nerve stimulation Patterns of Stimulation: 4. Post-tetanic facilitation:

Peripheral nerve stimulation Patterns of Stimulation: 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.

Peripheral nerve stimulation Patterns of Stimulation: 5. Double-burst stimulation (DBS): -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.

Peripheral nerve stimulation Patterns of Stimulation: 5. Double-burst stimulation (DBS):

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.

Methods used to quantify muscle responses  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.

Methods used to quantify muscle responses  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.

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Thank you Dr. Ahmed Mostafa