INTEGRITY TESTING OF COCHLEAR IMPLANTS IN THE AWAKE CHILD

Cochlear implantation is becoming a routine rehabilitation process for profoundly deaf adults and children. Often children are implanted at just two or three years of age and therefore the subsequent tuning of the device is challenging. Although some children demonstrate quick an d reliable responses to electrical stimulation, there are others who d o not respond consistently thus causing concern about the functioning of the device. It is therefore desirable to have an objective test of the integrity of the implanted electrodes. The principle of the integr ity test is the measurement of voltages generated by the biphasic curr ent pulses at the electrode array; this is accomplished using surface electrodes placed around the implanted ear, in conjunction with record ing and averaging equipment typically used for evoked response testing . Traditional integrity testing usually requires a general anaesthetic in young children, however this study demonstrated a simple, quick an d reliable method of obtaining results in the normally active child us ing ear-clip electrodes. Results are presented from 12 children tested in this way, and compared with results from 20 children who were test ed in theatre using a different electrode configuration. The tests wer e performed in common ground stimulation mode, but some measurements w ere also made in bipolar + 1 and pseudo-monopolar modes. The three sti mulation modes were compared, with the conclusion that common ground m ode provides an efficient check of implant function in the awake child , while pseudo-monopolar mode may be preferable for anaesthetized pati ents. In addition, measurements were made in vitro using a functioning cochlear implant in a saline tank in order to investigate the current flow during stimulation. The standard procedure in this department is to perform a full intra-operative integrity test on all. implanted ch ildren. The simplified technique is used to repeat the measurements po st-operatively if required.