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Nerve Stimulators -Peripheral (Train of Four)

Testing the Ulnar Nerve
  1. Wash hands.
  2. Extend the patient's arm, palm up, in a relaxed position.
  3. Apply two pre-gelled electrodes over the path of the ulnar nerve. Place the distal electrode on the skin at the flexor crease on the ulnar surface of the wrist, as close to the nerve as possible. Place the second electrode approximately 1 to 2 cm proximal to the first, parallel to the flexor carpi ulnaris tendon.
  4. Use caution in selecting the site of the electrode placement to avoid direct stimulation of the muscle, rather than the nerve.
  5. Plug in the lead wires to the nerve stimulator, matching the negative (black) and positive (red) leads to the black and red connection sites.
  6. Attach the lead wires to the electrodes. Connect the negative (black) lead to the distal electrode over the crease in the palmer aspect of the wrist. Connect the positive (red) lead to the proximal electrode.
  7. Turn on the PNS, and select a low current (10 to 20 mA is typical).
  8. Depress the TOF key, and through visual and tactile assessment, determine twitching of the thumb, and count the number of twitches. Do not count finger movements, only movements of the thumb.
  9. Maintain a consistent current with each stimulation.
  10. Discard used supplies, and wash hands.
Testing the Facial Nerve
  1. Place one electrode on the face at the outer canthus of the eye and the second electrode approximately 2 cm below, parallel with the tragus of the ear.
  2. Plug the lead wires into the nerve stimulator, matching the black and red leads to the black and red connection sites.
  3. Attach the lead wires to the electrodes. Connect the negative (black) lead to the distal electrode at the tragus of the ear. Connect the positive (red) lead to the proximal electrode at the outer canthus of the eye.
  4. Turn on the PNS, and select a low current (10 to 20 mA is typical).
  5. Depress the TOF key, and through visual and tactile assessment, determine twitching of the muscle above the eyebrow, and count the number of twitches.
  6. Discard used supplies, and wash hands.
 
Testing the Posterior Tibial Nerve
  1. Place one electrode approximately 2 cm posterior to the medial malleolus in the foot.
  2. Place the second electrode approximately 2 cm above the first.
  3. Plug the lead wires into the nerve stimulator, matching the black and red leads to the black and red connection sites.
  4. Attach the lead wires to the electrodes. Connect the negative (black) lead to the distal electrode 2 cm posterior to the medial malleolus in the foot. Connect the positive (red) lead to the proximal electrode 2 cm above the medial malleolus.
  5. Turn on the PNS, and select a low current (10 to 20 mA is typical).
  6. Depress the TOF key, and while observing the plantar flexion of the great toe, count the number of twitches.
  7. Discard used supplies, and wash hands.
  8. Determine the Supramaximal Stimulation (SMS)
  9. Increase the current in increments of 10 mA until four twitches are observed.
  10. Note the amount of current that corresponds to four vigorous twitches. Administer one to two more TOF stimuli.
 
Determine the TOF Response During NMBA Infusion
  1. Retest the TOF response 10 to 15 minutes after a bolus dose and/or continuous infusion of NMBA is given, initiated, or changed.
  2. If more than one or two twitches occur and neuromuscular blockade is unsatisfactory for clinical goals, increase the infusion rate as prescribed or according to hospital protocol, and retest in 10 to 15 minutes.
  3. Retest every 4 to 8 hours after the patient's condition has become clinically stable and a satisfactory level of blockade has been achieved.
 
Troubleshooting When There Are Zero Twitches
 
  1. Change the electrodes, and ensure that the patient's skin is clean and dry and without significant edema.
  2. Check the lead connections and the PNS for mechanical failure, and change the battery, if necessary.
  3. Increase the stimulating current.
  4. Retest another nerve (the other ulnar nerve or a facial or posterior tibial nerve).
  5. If there are no other explanations for a zero response, check the NMBA infusion for the rate, dose, and concentration. Reduce the infusion rate of the NMBA as prescribed or according to hospital protocol.

 

  

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