PATTERNS OF NERVE STIMULATION
For evaluation of neuromuscular function the most commonly used
patterns of electrical nerve stimulation are single-twitch, train-of-four (TOF),
tetanic, post-tetanic count (PTC), and double- burst stimulation (DBS).
Single-Twitch Stimulation
In the single-twitch mode of stimulation, single supramaximal
electrical stimuli are applied to a peripheral motor nerve at frequencies ranging
from 1.0 Hz (once every second) to 0.1 Hz (once every 10 seconds) ( Fig.
39-1
). The
Figure 39-1
Pattern of electrical stimulation and evoked muscle responses
to single-twitch nerve stimulation (at frequencies of 0.1 to 1.0 Hz) after injection
of nondepolarizing (Non-dep) and depolarizing (Dep) neuromuscular blocking drugs
(arrows). Note that except for the difference in
time factors, no differences in the strength of the evoked responses exist between
the two types of block.
response to single-twitch stimulation depends on the frequency with which the individual
stimuli are applied. If the rate of delivery is increased to more than 0.15 Hz,
the evoked response will gradually decrease and settle at a lower level. As a result,
a frequency of 0.1 Hz is generally used. Because 1-Hz stimulation shortens the time
necessary to determine supramaximal stimulation, this frequency is sometimes employed
during induction of anesthesia; however, the apparent time of onset and length of
neuromuscular blockade depend on the pattern and duration of stimulation. Therefore,
results obtained using 1-Hz single-twitch stimulation cannot be compared with results
obtained by using, for instance, 0.1-Hz single-twitch stimulation or TOF stimulation.
[13]
