Clinical Accuracy and Safety Using the SynchroMed II Intrathecal Drug Infusion Pump

BACKGROUND AND OBJECTIVES: We evaluated the infusion accuracy and device-related safety of implantable drug infusion pumps in subjects with chronic pain or severe spasticity. METHODS: Nine centers in the United States enrolled patients receiving intrathecal drug delivery systems to manage chronic pain and/or severe spasticity. Infusion accuracy was assessed at 6 and 12 months by comparing syringe-measured delivered volumes to programmer-predicted volumes. Safety was evaluated through analysis of adverse events. Separate laboratory testing conducted by the manufacturer also evaluated infusion accuracy. RESULTS: Eighty of 82 enrolled subjects were implanted. Sixty-five and 54 subjects, respectively, were analyzable for accuracy at 6 and 12 months. On average at 6 months, the pumps were measured to have delivered 1% more than the programmed delivery volume. Analyzed on a per-refill basis, the pumps delivered, on average, 2.5% more than the programmed delivery volume. Differences between per-refill means versus per-subject cumulative means were due to limitations in clinicians’ ability to precisely visualize single small syringe-volume differences, or possibly incomplete withdrawal of fluid from the pump. Laboratory testing demonstrated a per-refill mean accuracy error of minus 2.4%. Because average observed flow-rate error at 6 and 12 months (1% overinfusion) was derived from pump residual volume measurements by syringe and carried out in a clinical setting, clinical volume ratios were larger than direct volume measurements by weight observed in the laboratory. No deaths, permanent injuries, or unanticipated adverse device effects occurred. CONCLUSIONS: The pump accurately delivered intrathecal medication in the clinical setting of this study. Adverse events were similar in nature and severity to those described in the product labeling and literature.