[Implantable drug pumps for spinal opioid analgesia: technical solutions and problems]

Among the many technical appliances for pain therapy which are currently available, the use of implantable drug pumps for prolonged pain treatment is of increasing importance. Since this kind of pain therapy can be used without any problems outside the hospital, it improves the quality of life of the patient. Furthermore, it is combined with a reduction of side-effects which frequently occur when analgesics are given orally or parenterally in big single doses. High initial costs are compensated by a good cost-benefit ratio of this kind of pain treatment, which enables the use of analgesics in low doses in out-patients. Based on the use of gas mixtures which can be compressed repeatedly, implantable mechanically-driven pumps are a nearly inexhaustible propulsion unit for drug infusions. The development of new gas mixtures and of innovative control mechanisms allows greater independence from surrounding influences and higher precision regarding infusion rates. Mechanically-driven pumps are characterized by prolonged functioning and low cost of purchase. Therefore, they will continue to be available on the medical market in future. Special progress in cardiac pacemaker therapy as well as further miniaturization of portable infusion pumps with peristaltic propulsion have led to the development of programmed implantable pumps with lithium batteries as energy sources. The advantages of these pumps, particularly those with "externally" programmable infusion rates (continuous, bolus, periodical bolus, etc.) point to the future. With these devices, evacuation and refilling of the pumps due to necessary changes of drug concentrations, as has to be done with mechanically working pumps with fixed infusion rates, are no longer necessary. Therefore, these programmable pumps can also be used for infusion of drug concentrates. At present, however, high costs and the battery-dependent limited duration of functioning of these devices are disadvantageous. As with cardiac pacemakers, battery exchange is necessary. Using implantable drug pumps, relevant changes of body temperature and atmospheric pressure lead to more or less considerable deviations of the infusion rates. These deviations differ from product to product and can be studied in the informative material published by the manufacturer.