Pump Implantation
Once it has been established that intrathecal baclofen would be of use in managing an individual’s limb hypertonia, the surgical implantation of the delivery system is scheduled. In the case of younger children, a preliminary surgery may be required for the implantation of a CSF access device to be used in place of a spinal tap to deliver the drug to the CSF space. This allows the physician to test the effectiveness of intrathecal baclofen in patients with spinal fusions or other situations that preclude a spinal tap.
Currently, the most widely used pump is manufactured by Medtronic, and it comes in two different sizes. Both have the diameter of a hockey puck (3 inches in diameter), with one being slimmer than the other. The larger pump weighs about 6 ounces, and the smaller is about 4 ounces. They are usually implanted above and either to the left or right of the belly button under the skin and fat of the abdominal wall, resting either just above or below the sheath of the abdominal muscles. A needle is then used to introduce the catheter into the lower back's spinal fluid column so that the tip of the catheter overlays the portion of the spinal cord responsible for function of the targeted muscles. The catheter is then tunneled under the skin from the back to the side and around to the pump in the front where it is attached.
Once the surgical incisions are closed, the pump is adjusted to deliver the drug at a rate based on the amount of drug shown to be effective during the trial phase of evaluation. The rate of delivery is then optimized over the next several days in the hospital. This is done using an antenna that can broadcast signals to a tiny receiver within the shell of the pump. The antenna is a handheld disk that rests on the surface of the skin over the pump. It is connected to a portable computer that can read information stored within the pump about the amount of drug present within its reservoir, the rate at which it is delivering the drug and the concentration of the drug as prescribed by the physician when it was inserted into the pump. The computer can then alter the delivery rate by sending new signals to the pump via the antenna.