Intraoperative High Impedance Levels During Placement of Deep Brain Stimulating Electrode

Deep brain stimulation (DBS) is a well-established treatment for medically refractory Parkinson's disease (PD), essential tremor (ET), and dystonia. The field of DBS is expanding and techniques are under investigation for the treatment of several neurological disorders. A critical component of the success of these procedures depends significantly on the reliability and durability of devices implanted. Immediate feedback during surgery often gives the surgeon and patient a sense of confidence of long term success. When impedances are found to be elevated during the implantation of the DBS leads, appropriate trouble shooting measures are critical.

We present a 73-yr-old male undergoing awake subthalamic DBS with microelectrode recordings for severe PD. Once the optimal trajectory and depth were ascertained, the permanent DBS electrode was placed. High impedances were recorded. Troubleshooting procedures were performed and were all negative as to the cause of the values. Correct impedance levels of the DBS electrode was confirmed with extracranial testing, but continued high values were found again with intracranial positioning of the electrode. A postoperative computerized tomography (CT) scan confirmed intracranial air surrounding all of the contacts. The patient went on to outpatient programming with excellent clinical results.

The presence of pneumocephalus surrounding the DBS lead contacts at the target nucleus may have accounted for the intraoperative impedance findings. When all troubleshooting checks have not identified an explanation for the high impedances, intraoperative imaging may demonstrate pneumocephalus around the lead contacts, which should resolve and impedances return to normal values.