Device Related Complications

The most frequently reported complications with implantable pump systems involve some failure in the system itself. Early reports noted many catheter-related complications.7,35 This problem seems to have decreased in frequency16 with the development of more thick-walled and reinforced catheters, new anchoring techniques, and the use of paraspinous approaches to placement.

Catheter tip obstruction or replacement can be a problem and may require revision of the catheter. This problem is usually suspected when comparison of the expected and actually measured residual volumes vary by more than 20%. A complete evaluation of the catheter must be performed if obstruction, kinking, or separation is suspected. This is made more important by the increasing reports of sterile granuloma-tous masses forming at the tip of the catheter. These may present as an obstruction, but most commonly they are productive of increasing pain and progressive neurological deficit.17

Evaluation of a catheter problem calls for some type of imaging. Simple radiography with a soft tissue technique will demonstrate breakage or suggest a kink, migration, or disconnection from the extension or pump catheter. The evaluation of either suspected obstruction due to an intraspinal problem or catheter leakage requires the use of the injection side port, if present. Injection of nonionic contrast material will confirm obstruction and often show the point of leakage. The risk of this technique is the delivery of a large bolus of medication directly into the subarachnoid space, leading to the possibility of significant overdosage. Thus preparation for management of overdose should be made before such injections are begun. To avoid this problem, an attempt should be made to aspirate the catheter before the contrast is injected. In the absence of a side port, it is more difficult to evaluate catheter problems. A radioisotope may be injected into an emptied pump and a bolus programmed into a programmable pump or, an appropriate time may be allowed to elapse and the catheter scanned in the case of a nonprogrammable device.

Treatment of catheter problems usually requires removal and replacement of the catheter. Occasionally, a disconnected catheter may simply be reconnected, usually under local anesthesia. The demonstration of a granulomatous mass may require neurosurgical intervention to resect the lesion.

Pump-related complications common to nonprogrammable and programmable systems include overfilling of the pump, failure of the self-sealing septum at the refill port, and movement of the pump in the pocket. Overfilling can result in overpressurization, with the delivery of an unpredictable amount of drug, failure of the system, or activation of the reservoir valve, which in turn prevents infusion with a programmable pump. Nonprogrammable pumps may show a slight decline in drug delivery as they approach their refill time, most likely because the pressure of gas against the bellows decreases as the Freon reaches the maximum volume it has to occupy. This behavior should be anticipated and may require a slight shortening of the refill time if the weaker dose is troublesome to the patient.

Programmable pumps have an additional set of potential problems owing to the internal modules and mechanical components necessary to this type of device. Battery failure, pump rotor failure, and failure of the telemetry or electronic modules may occur. The battery lifetime of the pumps has been quite acceptable, generally in the 3- to 5-year range. Battery depletion requires surgical removal of the existing pump and replacement with a new pump. Pump rotor stalls may be confirmed by taking a radiograph of the pump to show the rotor, programming a bolus dose, and repeating the radiograph 15 minutes later. The pump rotor should have turned 90° if the rotor is functioning. If a rotor is stalled, the pump must be replaced. Failure of the electronic or telemetry module will result in a pump that is unable to receive a change in programming. The pump will, however, continue to function as a nonprogrammable pump at its last prescription infusion rate. Decision to replace the pump is based on the need to make programming changes.

Movement of the pump in the pocket may result in dislodgement of the catheters, extension and/or intrathecal. The pump may rotate in the pocket, resulting in a coiling of the catheter much like a fishing reel, or it may flip in the pocket, resulting in a progressive winding of the catheter. Revision of the pump and possibly the catheters may be necessary if catheter movement is occurring. A flipped pump is usually noticed by the patient, but it may be noted and verified in the clinic at the time of attempted refill. Revision of the pump will probably be necessary, often requiring anchoring the pump. In one case in the author's clinic, an abdominoplasty was performed with good results.

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Essentials of Human Physiology

Essentials of Human Physiology

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