Test 2: Peripheral Nerve Stimulator Flashcards
When should you check twitches to determine paralysis?
-Before intubation, but after sedation (baseline)
-Prior to maintenance dosing
-Monitoring continuous infusions
-Determine reversal ability
What is peripheral nerve stimulation?
The delivery of a monophasic current to a peripheral nerve.
-Variable frequency and amplitude
-Uses ECG electrodes (Positive lead should ALWAYS be proximal)
-Helps prevent over/under dosing and residual paralysis in PACU
-Repeat doses of MR should be guided by PNS and clinical signs.
-Clinical signs may precede twitch response b/c of differing sensitivities to MRs between muscle groups or PNS malfunction.
What is the preferred PNS site for emergence?
Adductor Pollicis (Ulnar Nerve)
What is the preferred PNS site for intubation?
Orbicularis Oculi (Facial Nerve)
Why is the Adductor Pollicis the preferred site for emergence?
-Closely mimics upper airway musculature.
-If you have recovery at the AP, you have recovery at the diaphragm.
-Black electrode (negative) closest to the wrist (distal).
-Stimulation causes adduction of the thumb.
Describe proper placement of the PNS for monitoring of the Facial Nerve?
-One should be external to the eye (directly in line with the eye). Outer canthus, right in front of the hair line. Other should be in front of the tragus.
-Black electrode should be closest to the ear.
-Red should always be proximal (in relation to the heart).
-Want to see eyebrow moving. Jaw motion is too low, can cause injury to the tongue
-Goal is unilateral eyebrow twitch.
Why is the Facial placement preferred for intubation?
-Best predictor of vocal cords
What is important to know regarding PNS monitoring of the Tibial Nerve?
-Least reliable
-Stimulation causes dorsiflexion of the Flexor Hallicus (toe should move)
-Black electrode to the heel, below the internal malleolus
-Only utilized during maintenance phase. If bed is turned 180 deg away from you.
Describe the Single twitch Pattern
-1 stimuli for 0.2 sec at 0.1 0 1 Hz
-Gets 1 twitch
-Qualitative. Can establish baseline prior to drug admin
-Limited clinical usefulness (!)
-Can be repeated in about 10 sec (won’t deplete Ach at NMJ)
Describe Train-Of-Four
-4 stimuli at 2 Hz given over 2 seconds (0.5 sec apart)
-Gets 4 twitches (normally)
-As relaxation increases, twitches fade
-Not entirely sensitive. Reflects blockade from 70-100%. Qualitative data.
-Useful during onset, maintenance, and emergence.
-Can be repeated in 12-15 sec
Describe Double Burst
-6 stimuli total at 50 Hz over 0.8 sec.
-3 short, 50 Hz bursts over 20 microsec, followed by another 3 bursts 750 microsec later
-More sensitive than TOF for the clinical evaluation of fade.
-Can be repeated in 12-15 seconds
Describe Tetany (twitch pattern)
-250 stimuli at 50 or 100 Hz delivered over 5 seconds
-Sustained contraction for 5 seconds indicates adequate, but not necessarily complete, reversal
-Painful, use sparingly. Not on awake people
-Detects residual block
-Have to wait 2 minutes to be repeated (for more Ach to become available).
What is Post-Tetanic Potentiation?
1) Elicit a single twitch for baseline
2) Hit tetany button for 5 seconds at 50 Hz
3) Hit TOF after tetany and will see fade. However, the first twitch after tetany is much larger than the control twitch was.
Only seen with Non-depolarizing blocks.
Describe post-tetanic potentiation in a depolarizing block.
-No potentiation occurs
-Decreased amplitude across the board
-Control twitch is the same as post-tetanic twitches.
Describe post-tetanic potentiation in a Non-depolarizing block.
-Control twitch will be of reduced amplitude
-Fade occurs with tetany
-Positive potentiation of first post-tetanic twitch (stronger than control twitch)
-Fade occurs with post-tetanic TOF.
What is the effect of Single Twitch on a Phase I Block?
Decreased contraction
