Monitoring Neuromuscular Blockade

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Monitoring Neuromuscular Blockade
2
Peripheral Nerve Stimulation

• All patients receiving neuromuscular relaxants
  should have neuromuscular function monitored
  during surgery.

3
Patterns of Stimulation
4
Characteristics of Stimulus

• Monophasic (square) impulse
• Duration lt 0.5 MSEC

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Single Twitch (0.1 Hz - 1.0 Hz)

• Least precise
• Need baseline
• First indication 75-80 block
• Twitch disappears 90-95 block
• Also increases blood flow to area

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Tetanic Stimulation

• Repetitive high-frequency (30-100 Hz)
  stimulation
• Persistent muscle contraction
• Fade when NDMRs are used
• inhalation agents augment fade
• Posttetanic facilitation

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Train of Four Stimulation

• 4 impulses at 2Hz
• Most common use of stimulator
• Does not require baseline
• compares 4th twitch to 1st twitch
• T4/T1 ratio indicates fade

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Train of 4 Stimulation (Contd)

• Loss of twitches
• T4 70 - 75 block
• T3 85 block
• T2 85 - 90 block
• T1 90 - 95 block

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What are the Characteristics of

• Depolarizing block
• normal
• overdose
• Nondepolarizing block
• normal
• overdose

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Posttetanic Count

• Used when no twitches are present
• Technique
• 5 sec. 50 Hz tetanus
• pause 3 sec
• stimulate at 1 Hz
• count twitches

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Postetanic Count

• Number of twitches present is inversely related
  to the time of return of train of four

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Sites of Stimulation

• Adductor pollicis
• most common site
• 1 lead over ulnar nerve proximal to the wrist
• 2nd lead proximal to 1st or in olecranon groove
• look only at the thumb

13
Site of Stimulation

• Orbicularis oculi
• stimulate facial nerve
• electrodes near tragus
• may directly stimulate muscle
• not quantifiable

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Hints for Relaxant Use

• Check batteries prior to case
• use only recommended batteries
• Properly position electrodes
• Cords are usually ready for intubation before Tof
  is flat

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Hints for Relaxant Use (Contd)

• Document return of twitch following sux before
  giving a NDMR
• After patient is intubated, reduce loading dose
  of NDMR

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Hints for Relaxant Use (Contd)

• Titrate relaxant to twitch
• Do not reverse until at least 1 twitch has
  returned
• Document sustained tetanus after reversal