We asked experts to describe how both kinds of devices work and explain the issues involved in using them with acute and chronic pain patients. Here's what they said.
Two types of pumps
External reservoir pumps are battery-operated devices, about the size of a portable video game, connected to a subcutaneous catheter. Patients often wear them hooked to a belt. Michael Whitworth, MD, of the Pain Center at Columbus Regional Hospital in Columbus, Ind., explains how they work: "These devices typically have an elastic, expandable bulb- or spring-loaded syringe mechanism that contains the local anesthetics (either a narcotic or non-narcotic), which can be mixed with an adjunctive agent such as clonidine. They usually infuse for 24 to 72 hours and are then discarded, along with the subcutaneous catheter. Other external reservoir pumps include IV or PCA infusion pumps connected to epidural catheters that are tunneled into the patient. On rare occasions, the catheters are also used in other locations, such as peripheral nerves."
Implantable pumps, which are about the size of a hockey puck, rest completely within the body. They come in two varieties, programmable and non-programmable. Edson Parker, MD, managing director of the Pain Institute of Nevada in Las Vegas, explains how they work: "Programmable pumps run on batteries that can last from four to seven years. During the life span of the battery, the infusion rate can be re-programmed through the skin, using a computer with telemetry (radio frequency energy). The clinician holds a wand over the infusion pump and makes the changes, which takes less than five minutes. This makes management of pain and the medication much easier than with the non-programmables." Programmable pumps can be customized to deliver medication according to the patient's lifestyle, according to Dr. Whitworth. "For instance, if the patient typically has little pain while sleeping, the pump delivers much less drug. Approximately a half-hour before a pre-programmed ?wakeup' time, the pump will start to deliver more medication. If the patient wants to take a walk or exercise at the same time every day, which would usually result in an increase in pain, the pump is set to deliver even more medication." The downsides of these pumps are their cost (which can be as high as $12,000) and the fact that they need to be replaced, via another surgery, once the battery runs out.