The programmable implantable medication system (PIMS): design features and pre-clinical trials

This report describes the clinically significant design features of a variable rate implantable insulin infusion pump, the Programmable Implantable Medication System (PIMS), and its function in pre-clinical trials. PIMS has a number of unique features, including a solenoid, pulsatile pump design requiring minimal power (less than 15 microwatts) and a less-than-atmospheric pressure reservoir. Two-way communication is accomplished by radiotelemetry. The implanted device stores programs, and records its own hourly history of insulin delivery. Limits are set on total insulin delivery over time. Basal rates are adjustable, and patterned prandial insulin delivery curves can be programmed. Initial trials (3.1 dog-years) identified four problems which were corrected prior to final pre-clinical trials: microcracks in the diaphragm, a valve-seating leak, electronic failure of prototype microchips, and insulin aggregation. Sixteen dog-years of final pre-clinical trials with a single system design demonstrated that 5 pumps were still working continuously after up to 3.75 years (mean 3.3 years) without mechanical or electronic pump failure. The longest interval between reservoir refills was 5 months. Remaining potential causes of flow stoppage, however, include blockage of the peritoneal catheter by omentum (which occurred once), and air lock (which occurred two times).