1. 2007;10;533-540Is Impedance a Parameter to be Taken into Account in Spinal Cord Stimulation?
   Observational Report
   David Abejon, MD, and Claudio A. Feler, MD.

Background: Over the last few decades, spinal cord stimulation (SCS) has become one of the main treatments in the therapeutic arsenal available to pain treatment units. New stimulation systems have been developed and the indications of neurostimulation have been expanded. The premises for a successful technique remain the same; good patient selection, good surgical technique, and good management of electrical parameters when programming.

Design: An observational report.

Objectives: The primary objective of the study was to determine the relationship between changes in impedance (R) and energy requirement (E) elicited by changes in patients posture. The postures analyzed were supine (S), sitting (SI), standing (ST), and walking (W). As a second objective, the difference produced in the energy requirement when changing posture was analyzed.

Methods: A study was carried out in 70 patients with chronic intractable pain implanted with a neurostimulation system between January 2000 and March 2006. We define the perception threshold (Tp); the discomfort threshold (Td); and the therapeutic threshold (Tt). The amplitude of perception was measured in mA. With the resulting data, the therapeutic range (TR) was determined. After performing all measurements with the patient in the ST position, the neurostimulation system was shut off and the patient maintained in the other position for 5 minutes before performing the measurements. The variables R and E were compared by age groups, sex, implant duration, and the time since implant placement. Patients were divided into groups according to whether the location of the implanted electrodes was cervical or thoracic. The full analysis by age, sex, and implant duration was performed in the cervical and thoracic implant groups.

Results: No correlation was found between impedance and posture. When the results for R and E were analyzed by sex and age, no statistical differences were found in any of the values in any position. The analysis of time since implant greater than or less than 6 months did not find differences in the energy requirement, although there was a significant difference in the impedance value when patients were in the S position. No significant differences were observed in the analysis by age groups.