20 Monitoring NMT
294
CAUTION
NMT monitoring is intended as an adjunct in patient assessment and must be used in conjunction with
observation of clinical signs and symptoms.
NMT stimulation can be painful to a non-sedated patient. It is recommended not to stimulate before
the patient is adequately sedated.
Use only electrodes suitable for nerve stimulation deemed appropriate by the attending physician. Pay
special attention to current densities exceeding 2 mA r.m.s/cm
2
for any electrodes.
Stimulation Modes
The NMT module provides four stimulation modes:
•Train-Of-Four (
TOF)
•Single Twitch (
Twitch)
• Post-Tetanic Count (
PTC)
• Double-Burst Stimulation (
DBS)
Train-Of-Four (TOF)
In this mode four stimuli are applied every 500 milliseconds (2 Hz). Each stimulation of the train
causes the muscle to contract. The fade in the individual response to each single stimulation provides a
basis for evaluation. The NMT Module then calculates a TOF ratio (
TOFrat) value in % using the ratio
between the fourth and the first twitch. When fewer than four twitches are detected, the monitor
displays a TOF count (
TOFcnt) value instead, this represents the number of responses to the four
TOF stimulation pulses.
Post-Tetanic Count (PTC)
The Post-Tetanic Count stimulation pattern starts with a sequence of four current pulses, delivered
every 500 milliseconds (2 Hz). If a muscle response is detected, the PTC sequence is stopped and the
responses are reported as TOF measurement. If there is no muscle response, the sequence continues
with a five seconds long tetanic stimulation of current pulses delivered at 50 Hz, followed by a pause
of 3 seconds, followed by 20 single current pulses delivered every second (1 Hz). Muscle response
detection is active only during the first 4 single pulses and the last 20 single pulses. During the last 20
pulses, the
PTC value is incremented with each detected muscle response.
Single Twitch (Twitch)
If this mode is configured the NMT Module measures the response to single electrical stimuli applied
to peripheral motor nerves. The module sends a single pulse and measures the strength of the resulting
twitch, the module then calculates a Twitch Ratio (
Twitch) value in %. If the displayed numeric is 80,
the strength of the measured twitch was 80% of that of the reference twitch, see “Calibrating the NMT
Measurement” on page 296.
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