TwitchView® User Guide
TwitchView utilizes clinically-validated electromyography (EMG) to quantitatively monitor the patient's level of neuromuscular blockade. EMG measures the evoked action potential or the electrical response of the muscle. Unlike other quantitative monitoring modalities, EMG does not require motion and can be utilized when the patient's arms are tucked.
Tip: Monitor performance is dependent on proper placement of the electrode. For tips on electrode placement, watch the brief instructional video below.
Hand Placement:
- Locate the ulnar groove and place the stimulating electrodes directly over the ulnar nerve just proximal to the wrist crease.
- Wrap EMG electrodes 1 & 2 around the inside base of the thumb and press the curve down into the web space.
- Push 1 & 2 down onto the AP & FDI and affix G to the index.
Foot Placement:
- Locate the medial malleolus and place the stimulating electrodes over the posterior tibial nerve next to the bony projection.
- Affix 1 & 2 within the foot arch around the flexor hallucis brevis and affix G distally to the ball of the foot or big toe.
Tip: After connecting the electrode to the patient cable, place a 4x4 under the connection and tape in place.
For longer cases with tucked arms, reinforce the electrode with tape or coban to mitigate accidental electrode removal.
Train-of-Four (TOF): The measured response to four stimulation pulses.
–TOF Count (TOFC): The number of responses elicited, 0 to 4
–TOF Ratio (TOFR): The degree of fade or comparison of the 4th to the 1st twitch, when 4 twitches are present; T4/T1
Post-Tetanic Count (PTC): The measured response to 5-sec 50 Hz tetanic stimulation, when the TOFC = 0.
–PTC: The number of single twitch responses from 0 to 15 with lower numbers indicating deeper blockade
–Tip: PTC >10 typically indicates T1 will return within ~10 minutes
Note: To support continuous monitoring, TwitchView utilizes AutoPTCTM. When AutoPTC mode is on, TwitchView will automatically transition between TOF, the default mode, and PTC based on your patient’s real-time presentation.
How does AutoPTC work? Before every PTC, a TOF is performed. If a response is elicited, the monitor cancels PTC and resumes TOF monitoring.
Starting a Case
- Reset the monitor between every case. Menu → New Session → OK
- Connect the electrode to the patient cable. The Play button will turn green if the electrode check is passed, and red if the electrode is not inserted or if there is poor contact.
- Press play, after the patient is anesthetized but before administering NMBA to optimize settings and confirm electrode placement.
- After Start-up, TwitchView initiates TOF measurements @ 20-second intervals.
- The first time the TOFC = 0, AutoPTC is triggered.
Tip: Pre-paralytic start-up is recommended to confirm correct electrode placement and to allow the monitor to select the electrode with the largest EMG signal and set the optimal stimulating current. However, TwitchView can be utilized post-paralytic with default settings.
Confirming Electrode Placement
Typical Pre-paralytic EMG:
- Waveform is sinusoidal and large in amplitude
- TOFR ~100%.
Atypical Pre-paralytic EMG:
- Waveform is relatively flat
- Monitor indicates poor signal with a TOFR in parenthesis
Tip: If the EMG signal is poor or the monitor sets a high stimulating current (≥70mA), reposition the stimulation leads, start a New Session on the TwitchView and redo quickstart.
Watch the video below for an overview of TwitchView monitor function.
Managing Neuromuscular Blockade
Every time TwitchView takes a measurement, a data point is plotted on the trend plot. The trend plot enables you to visualize how neuromuscular blocking agents affect each patient differently. Using the trend plot, you can proactively manage the patient's level of blockade intraoperatively—redosing NMBA according to the individual patient's response and the required surgical conditions.
Tip: To view the trend plot, touch the box in the bottom left corner of the TwitchView display. The most recent data point will always be to the right of the plot near 0. You can adjust the trend plot timescale by pressing 15m, 30m, 1hr, 2hr or 8hr and scroll back by pressing the blue arrow.
The level of neuromuscular blockade increases from the top to the bottom of the plot.
- A dot in green indicates a TOFR of >90%
- A dot in black indicates TOFR <90%
- A dot in light gray indicates a TOFC
- The trend plot pictured indicates periods to expect relative muscle recovery rates.
Reversal
Many institutions implement literature-based reversal guides to use the information provided by TwitchView to 1) select the appropriate reversal drug and 2) dose the selected reversal in accordance with the patient's real-time need.
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Clinical Expectations
Patient response to NMBA is variable.
- A typical dose of rocuronium (0.6 mg/kg) has a median clinical duration of 31 minutes in adults, but the duration can vary substantially from patient to patient and range from 15 to 85 minutes.3
Facial assessments are susceptible to direct muscle stimulation, and facial muscles recover quickly.
- A TOFC 4 on the face may be accompanied by a TOFC 1 or PTC at the hand.1
It’s common for patients to breathe spontaneously in PTC.
- Normal end-tidal CO2 and tidal volumes are also common during profound neuromuscular blockade
Recovery of the Adductor Pollicis aligns with the recovery of the upper airway.1
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The clinical standard for “adequate recovery” is a TOFR ≥0.9 measured at the adductor pollicis muscle.
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