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Neuromuscular transmission
ElectroSensor and electromyography (EMG)
Measurement with ElectroSensor is based on electromyography. Three electrodes are
placed on the muscle, and the innervating nerve is stimulated. The recorded electrical
activity of the muscle is inversely proportional to the degree of block.
Stimulation modes
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Train of four, TOF: Recommended for most cases. It is also the default setting.
●
Double burst stimulation, DBS: Useful when using the MechanoSensor. It enables
better visual observation of the fading in responses.
●
Post tetanic count, PTC: Used for estimating the relaxation level with tetanic
stimulation.
●
Single twitch, ST: Single twitch mode is practical when using depolarizing relaxants:
in these cases, TOF% does not give any additional information about the patient
status.
How to interpret the NMT values
When neuromuscular block deepens, different stimulation modes may be needed to
assess the relaxation status. The following table describes the depth of relaxation.
100 TOF% 20
4
Count 0 10 PTC 0
Light
RELAXATION METER Deep
Train of four (TOF) mode
In TOF stimulus mode, four stimulation pulses are generated at 0.5 second intervals.
The response is measured after each stimulus and the ratio of the fourth to the first
response of the TOF sequence is calculated, resulting in TOF%.
With the ElectroSensor, T1% is displayed. If the reference is successfully found, a scale
is also included. Scale markers represent 0%, 25%, 50%, 75% and 100% reference
values. When no reference is available, no T1% value is displayed and the bars are
not scaled.
When relaxation deepens, the TOF% declines until the fourth response disappears and
no TOF% is available. The degree of neuromuscular block is then estimated from the
number of responses, the count, which represents the number of responses detected
to the four stimuli. The fewer the responses, the deeper the relaxation.
Number of responses, count Neuromuscular block Muscle power (% of control)
1 95% 5%
2 90% 10%
3 85% 15%
4 75% 25%
Double burst stimulation (DBS) mode
DBS consists of two separate bursts. Each burst consists of three consecutive pulses
at a 50 Hz frequency. The response ratio of the second to the first burst is calculated,
resulting in DBS% (equivalent to TOF%).
2062971-001 CARESCAPE Modular Monitors 369