Surgical Technique: Intrathecal Medication Delivery System Implantation

Surgical Planning/Preoperative Considerations

Planning for the implantation of an implantable drug delivery system (IDDS) requires considerations for the prevention of hardware infection, ergonomics of system function and comfort of the patient, prevention of pump pocket and catheter complications, and prevention of cerebrospinal fluid (CSF) leak.

An IDDS consists of an intrathecal (IT) segment of catheter, a subcutaneous segment of catheter, and an implanted pump. The IT and subcutaneous catheter segments may be either part of the same catheter (one-piece catheter) or separate catheters joined with a connecting pin (two-piece catheter system). The choice of either a one-piece catheter or two-piece catheter system is determined by the preference of the implanter. A one-piece catheter eliminates the need for connecting pins and the related considerations that go with connecting two catheters together including assuring that the two catheters will not pull apart, etc. A one-piece catheter is also longer in total length than the IT segment of the two-piece system and thus can be used to reach higher vertebral levels (upper thoracic or cervical) that may be difficult to reach with a two-piece catheter system. Conversely, a two-piece catheter system may be easier to handle when revising the IT catheter because the IT portion may be disconnected and interrogated in the back, unlike the one-piece system, which must be cut and then connected with a new connecting pin following open interrogation or replacement of part, unless an entirely new one-piece catheter is implanted. There are newer two-piece catheter systems that are longer (like the one-piece systems) and are segmented into a very long section that is implanted into the IT space and then tunneled to the abdomen and a very short section that essentially becomes only the pump connector.

Given that the pump footprint is somewhat large, the placement location of the pump is not a small consideration both technically and, to the patient, cosmetically and ergonomically. The most common programmable pump for implantation in the United States is the Synchromed II (Medtronic, Inc., Minneapolis, MN), which comes in two sizes and holds either 20 mL or 40 L of medication. It is my opinion that when using these programmable pumps, patients should be shown models of each pump so that they can grasp the magnitude of the implanted device and can express their opinion as to which size they prefer, understanding that the smaller-capacity pump must be refilled more often. These two pumps have the same footprint, but the actual thickness difference between the two pumps is not great: 19.5 versus 26 mm, respectively. The Prometra II pump (Flowonix Medical, Mt. Olive, NJ) is 69 mm in diameter and 24 mm thick and holds 20 mL.

The patient should be queried as to the usual location of the waistband of their pants, as it is desirable to prevent this from rubbing on the pump and contributing to erosion of the hardware through the skin. The pump should be sited on the patient in both the supine and seated positions, to ensure that it will be placed in a position that is comfortable for the patient. The pump should affect neither the lower costal margin nor the iliac crest. For most patients, the pump may be comfortably placed in a paramedian location with the superior aspect near the level of the umbilicus, adjusted as needed for individual anatomy. When possible, the site of implant should be chosen so as to avoid other implanted devices such as ventriculoperitoneal shunts, gastrostomy tubes, and other implantable devices such as an implantable pulse generator for spinal cord stimulation. If a pump is being reimplanted following removal of a prior one due to infection, it is desirable to use the contralateral abdomen if possible.

While pump pocket or hardware infections are rarely life threatening, they result in interruptions in therapy, further trips to the operating room, increased healthcare costs, and frustration for all involved. It is rare to salvage an infected pump, although there are reports of this salvage occurring in the literature ( ). Patients must be free of infection at the time of implantation. This includes urinary and respiratory tract infections, as well as infected decubitus or other skin ulcers. Most pump infections are due to skin contaminants, such as Staphylococcus sp. Preoperative bathing for several days with a solution containing chlorhexidine gluconate may decrease skin colonization with both sensitive and antibiotic resistant organisms ( ). Intranasal mupirocin ointment, twice daily, may help decrease the rate of intranasal carriage of resistant Staphylococcus sp. ( ). Antibiotics such as cefazolin or oxacillin, which cover common skin organisms, are usually sufficient for prophylaxis; however, some physicians recommend that all patients be given vancomycin preoperatively to cover methicillin-resistant Staphylococcus aureus (MRSA) bacteria.

It is my opinion that preoperative cross-sectional imaging studies (either magnetic resonance imaging [MRI] or computed tomography [CT]) should be obtained from the planned catheter insertion site to the proposed tip location so that the surgeon may have advance knowledge of any anatomic variants or barriers to catheter insertion or passage. The level of the conus should be noted.

Positioning and Surgical Preparation

The patient is placed on the operating table in the supine position. After the induction of general endotracheal anesthesia, the pump implant site is then marked on the abdomen (if this has not been done before coming to the operating room). It is important to do this before the patient is turned into the lateral decubitus position, as the abdominal skin can shift greatly, especially if the patient has a pendulous abdomen. The patient is turned into the lateral decubitus position with the planned pump implant side up. An axillary roll is placed to relieve traction and pressure on the brachial plexus. Padding is also placed between all bony protuberances to prevent pressure and possible sequelae including pressure sores. Both arms are placed such that they are as far superiorly as is comfortably possible for the patient. This facilitates visualization of the spine and catheter with fluoroscopy. The lower arm is either placed on an arm board and the upper one on an “airplane-type,” arm holder or both arms, separated by padding, are placed in the “praying mantis” position and secured in that position. Each arm is thoroughly padded to prevent pressure on the ulnar nerves.

Some surgeons secure the patient in the lateral decubitus position using wide cloth tape, and some secure the patient in that position using a “beanbag.” If a beanbag-type pad is used, it may be wrapped around the patient and suction applied to harden it and support the patient. Care should be taken in doing this so that neither the lumbar nor the abdominal operative site is obscured by the bean bag. The beanbag should not rise as high as the lumbar spinous processes or the umbilicus. Care should also be taken to ensure that sharp points to not cut into the patient. Sturdy fabric tape is applied across the patient’s hips (padded as well) to prevent rotation during the procedure.

The fluoroscope is brought in, and anteroposterior images are obtained. The fluoroscope should be aligned to the patient’s spinal anatomy such that the spinous processes are centered between the pedicles and the vertebral end plates are visualized, end on. In patients without prior lumbar fusion, the catheter is often inserted at the L1-2 or L2-3 interspace. For this, the incision should be centered over the skin representation of the L3 or L4 pedicle, respectively, on the side of the pump implant, so that the catheter does not cross the midline.

There are many methods to surgical preparation. This author’s preferred technique involves initial skin decontamination with isopropyl alcohol, followed by marking of the lumbar incision and remarking of the abdominal incision. The operative field is then outlined with a border of Mastisol solution (Ferndale Labs, Ferndale, MI). Plastic drapes (Number 1010, 3M, St. Paul, MN) are then placed to isolate the operative field. A typical scrub and paint preparation is then performed with either povidone-iodine or chlorhexidine solutions. Once the paint has dried, the incisions are remarked with a sterile surgical marker, and a layer of Duraprep (3M) or Chloroprep (CareFusion; Becton Dickinson, Franklin Lakes, NJ) is applied. The operative field is outlined in sterile towels, and an iodine-impregnated drape (Ioban 2; 3M) is applied before the final draping. Double gloving is used during the procedure, and outer gloves are changed after draping and before starting the procedure.

After a time-out procedure, the incisions are infiltrated with generous amounts of local anesthetic. This author prefers a 1:1 mixture of lidocaine with epinephrine (1:100,000 or 1:200,000) and 0.5% bupivacaine because of its combination of rapid onset (due to the lidocaine) and long duration (due to the bupivacaine).