3.2
Cable connections (subjective monitoring)
When the acceleration transducer is not connected to the TOF-Watch, the instrument can be
used as a peripheral nerve stimulator.
When surface electrodes are used, the instrument automatically uses stimulation pulses of
200 µs (300 µs) at 0 - 60 mA (0 - 12/18 µC).
Instead of the patient response, the TOF-Watch automatically shows only the stimulation
strength in mA (µC) and stimulation mode.
The pre-defined default stimulation strength is set at 50 mA. Attach the stimulation cable to
the surface electrodes placed on the ulnar nerve (see above), and connect to the designated
color-coded outlet on the TOF-Watch (insertion of the cable in the wrong outlet is not possible
because of a mechanical barrier).
3.3
Cable connections (loco-regional anesthesia)
When the special cable for a needle electrode is used, the TOF-Watch can be used for nerve
location in loco-regional anesthesia.
The TOF-Watch will automatically revert to the loco-regional anesthesia mode, enabling
stimulation with a pulse width of 40 µs and a current ranging between 0 and 6.0 mA.
The total charge delivered varies between 0 and 0.24 µC. In the set-up menu, display of the
strength of the stimulation can be switched from µC (pre-installed) to mA.
The pre-defined default setting is 0 µC. Patient responses are not shown on the display.
Attach the special cable to a needle electrode and a surface electrode, and connect to the
designated color-coded outlet on the TOF-Watch (insertion of the cable in the wrong outlet is
not possible because of a mechanical barrier).
3.4
Electrodes
When monitoring neuromuscular transmission, the TOF-Watch should always be used with
round surface electrodes with snap connection. Small (pediatric) electrodes are advisable to
obtain a sufficient current density. In order to ensure a steady quality of the test, be sure only
to use CE marked electrodes.
3.5
Electrode placement
Acceleromyography can take place by stimulating the facial nerve and monitoring the response
of the orbicularis oculi muscle or by stimulating the posterior tibial nerve and monitoring the
response of the flexor hallucis brevis muscle. However, stimulation of the ulnar nerve and
acceleration measurements at the adductor pollicis is preferred for routine monitoring.
The electrodes are placed over the ulnar nerve on the volar side of the wrist. The distal electrode
is positioned where the proximal bending line crosses the radial side of the flexor carpi ulnaris
muscle. The proximal electrode can be placed either 2 to 3 cm proximal of the distal electrode
or over the ulnar nerve at the elbow.
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Correct positioning of the electrodes is important. Small displacements may result in
considerable changes in stimulation current requirements. Furthermore, the electrodes must
be positioned in such a way to avoid direct stimulation of the muscle.
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Place the electrodes on each side of the expected position of the ulnar nerve. In this way,
the effect of any minor misjudgment of the actual nerve position is minimized.
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It has been found that slight pressure on the electrodes may improve the stimulation
considerably. Therefore, taping the electrodes to the skin may be advisable.
8
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TOF-Watch S
Operator manual 33.516/A
