The presence of abundant opioid mu receptors in the dorsal horns of the spinal cord was discovered in the 1970s. Subarachnoid injection of morphine was soon utilized to control cancer pain. Since intrathecal delivery of opioids provides direct access to the mu receptors, a much lower dose can achieve analgesia than by other routes of delivery. Thus, significant activation of systemic mu receptors, such as occur in the gut, is avoided thereby reducing unwanted side effects of opioid therapy such as constipation. The first clinical use of an implanted intrathecal drug delivery system (IDDS) was described in 1981. Introduction of effective bacteriostatic filters allowed safe long-term infusion. By 1991, commercially available fully programmable implanted IDDS became available (Medtronic, Inc, Minneapolis, MN).
Presently, commercially available pumps fall into two categories: continuous infusion and programmable rate devices. Several continuous infusion devices have been approved by the FDA (eg, Codman 3000, Codman and Shurtleff, Inc, a Johnson & Johnson Company, Raynham, MA, US). At present, the only programmable IDDS approved for pain indications in the US is the SynchroMed family of pumps (Medtronic, Inc, Minneapolis, MN).
CONTINUOUS INFUSION PUMPS
Continuous infusion pumps are typically designed as two compartment devices.
Inner compartment containing the drug to be administered
Outside chamber, which is filled with a 2-phase fluorocarbon propellant, which applies continuous pressure to the inner compartment.
Filling the drug reservoir compresses the propellant and this pressure drives the drug from the collapsible chamber through a flow restrictor and then into the patient’s spinal catheter.
Flow rates are factory preset.
The advantage of a continuous flow rate device is that it does not require an energy source or complex programming circuitry and therefore does not need replacement because of battery life or utilize a specialized programmer.
The main disadvantage is that any dosage adjustment requires emptying and refilling the pump with a newly formulated drug concentration. Additionally, potential clinical advantages such as timed bolus dosing, varying flow rates, and on-board storage of clinical data are not possible.
There are several mechanical, continuous infusion pumps that have been available in the United States. For example, Infusaid (Pfizer Hospital Products Group, Inc) and Isomed (Medtronic, Inc) are no longer available (Figure 65-1). At the present time, the Codman 3000 (Codman & Shurtleff, Inc, Raynham, MA) formerly known as Arrow 3000, and prior to that as Therex 3000, is the only approved mechanical pump in the United States (Figure 65-2).
Codman 3000—16 mL (left), 30 mL (center), and 50 mL (right).
CODMAN 3000 INFUSION PUMP
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