Cochlear SPrint Sound Processor Informações Técnicas descarregar pdf (Página 52)

SECTION ONE | CLINICAL GUIDANCE

• Alternating stimulus polarity will effectively reduce the stimulus artefact.

However, there may be a disadvantage if the evoked brainstem responses

from negative and positive leading stimulus pulses have different

response latencies. This can be reduced by using narrow pulse widths, for

example, 25 μs.

(Absence of an EABR does not mean that the implant is not working or that

the individual will not stimulate postoperatively.)

1.14.2 Cortical Evoked Potentials (CEP)

Cortical Evoked potentials can be recorded in a similar manner as EABR.

Practically, the only difference between EABR and CEP is the time between the

stimulation pulse and the recording window. Typically, the EABR signal occurs

at 1 – 10 ms after the stimulus while the CEP signals can be recorded between

100 and 500 ms. Clinically, CEP is usually more associated with perception

(conscious), while EABR is merely a sign of detection (unconscious).

1.14.3 Electrical Stapedius Reﬂex Test (ESRT)

The acoustical stapedius reﬂex is a small movement of the stapedius muscle in

the middle ear that is elicited by loud (>80 dB SL) acoustical stimulation. The

ESRT can be tested with an implant recipient and is generally believed to have

a correlation with C-level. There are two ways to measure ESRT thresholds:

Method 1: Visual inspection ESRT

During surgery, after the electrode has been placed and with the skin ﬂap still

open, the implant can be stimulated and the surgeon can look for a stapedius

reﬂex by visual inspection of the stapedius tendon or the middle ear ossicles.

Please keep in mind the following tips:

• Make sure the monopolar reference electrodes are covered to get a good

electrical connection. Preferably test the impedance ﬁrst. If needed, use

saline to improve the electrical contact.

• Do not use a muscle-relaxing agent since this will suppress the ESRT.

Method 2: Impedance bridge testing of ESRT

When using this method, an electro acoustic immittance meter is connected

to either the contra- or the ipsilateral ear. By measuring the impedance change

during the electrical stimulation, a response can be observed. To use this

method, use your immittance meter in free running mode and observe for

changes in the impedance when stimulating. A trigger is also made available

by the system, should you use equipment that needs to be triggered for

measurements. This trigger functionality is similar to the description given for

EABR measurements.

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