Atrotech Atrostim PNS Anwenderhandbuch Seite 23

Surgical procedure Atrostim PNS
5 PRECLOSURE TESTING / CHECKING OF THRESHOLD CURRENTS
Prior to closure, the threshold currents of each electrode combination are checked
one combination at a time. For the test set-up see Appendix 1, page 19. The threshold
current is increased gradually (in 0.3 mA steps) until first diaphragmatic twitches are
observed (by visual checking, fluoroscopy, ultrasound, or acceleration meter) (Glenn,
Sairenji 1985). Because during this testing only one combination is active the pulse
interval is four times as long as indicated on the programming module. This causes
vibration, which helps to differ threshold movements from other unintended muscle
twitches. At suprathreshold current a vibrating strong diaphragm contraction should
occur. Now current is decreased in smaller steps (0.1 mA) until the threshold level is
reached again. First twitches should occur at the same time when the first stimulus
pulses are heard. The threshold current value is recorded (see Form 1 - Patient
Forms).
Repeat the procedure with the other three combinations, and at the other side. The
unipolar threshold current values should be in the range of 0.5 to 2.0 mA. The
difference between the lowest and highest threshold current should not exceed 1 mA.
If the difference is larger, slight re-positioning of the corresponding strip will change
the difference to an appropriate level. Once the above mentioned values are achieved
the electrodes have been placed correctly and symmetrically.
If a programming module switch fails, it may cause wrong programming of the
stimulus controller. Therefore, the operator of the programming module must
observe closely the effect of any change he/she makes in the module parameters, and
watch for any discontinuity or nonlinear functionality.
6 IMPLANT STIMULATOR PLACEMENT
The site for the implant stimulators has to be chosen individually for each patient. In
adult patients, a firm ground should be chosen, over the anterior lower rib cage or
below the clavicle as for heart pace-makers (Wetstein 1987). However, for the latter
location it should be kept in mind that the energy transfer coil needs a flat surface.
The anterior lower rib cage, on the other hand, may interfere with chest
physiotherapy. But these places are more safe in prevention of implant stimulator
displacement, which may cause troubles when the patient gains weight (Baer et
al.1989). The medial borders of the implant stimulators should be at least 15 cm
apart from each other to avoid cross talk of transfer coils and stimulators.
In pediatric patients and in slim adult patients placement of the implant stimulators to
anterior abdominal wall should be avoided because of linear growth of the patient or
because of body movement, which may cause excessive mechanical stress on the
electrode or the extension lead.
14
April 2008