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Analgesic infusion pumps intended for implantation that are designed for use in the administration of analgesics into the spinal fluid space (i.e., intrathecal). These pumps are frequently battery-powered devices. They are comprised of a syringe-driven mechanism that is inserted between the skin and the muscle of the lower abdomen; an infusion rate controller; and an internal reservoir containing the analgesic solution. The analgesic solution is delivered from the pump to a subcutaneous tube and then to a catheter with a needle at the distal end that is typically inserted in the intrathecal space. Intrathecal implantable pumps that deliver the analgesic without the use of batteries are also available; they are based on a two-chamber pump with an inner chamber containing the analgesic drug and an outer chamber containing a propellant. The temperature of the patient warms the propellant which in turn exerts a constant pressure on accordion-like bellows that divide both chambers. The pump must be also able to deliver a continuous or intermittent flow and/or deliver bolus doses of analgesics when necessary. Intrathecal analgesic infusion pumps are used mainly by patients with otherwise intractable chronic pain. These pumps may be used also to administer drugs (e.g., baclofen) for refractory spasticity.
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