The implantation procedure may be accomplished under general or local anesthesia with anesthesia monitoring. The latter technique is of-
Surgical Implantation Technique 283
ten preferred in an outpatient setting because it lends itself to rapid recovery following the procedure.
Prior to implantation, some time should be spent with the patient to optimize the side and location of the pump. About the only area amenable to the implantation of these generally large devices is the right or left lower quadrant of the abdomen. Some time should be spent with the patient preoperatively discussing which side and where the pump will be placed. The anatomical constraints tend to be the iliac crest, the symphysis pubis, the ilioinguinal ligament, and the costal margin. These structures should not contact the pump with the patient in the seated position. The task is easier in more obese patients and can be very difficult in cachectic cancer patients.
The patient is positioned on the operating table in the lateral decu-bitis position, with the implantation side upward. At this stage C-arm fluoroscopy may be necessary if a new intrathecal catheter is to be placed. The instrument is positioned to allow an anterior-posterior view for an easy lumbar puncture and identification of the catheter tip level. A 5 cm incision is made in the skin, down to the lumbar fascia, and then the catheter is implanted through a paraspinous approach. A good flow of spinal fluid is documented, the catheter is clamped to the drape to prevent CSF loss, and the incision is packed with an antibiotic-soaked sponge.
If the existing catheter is to be used as the permanent delivery catheter, the patient is positioned on the operating table in the decu-bitis position with the implant side upward and the exiting screening extension catheter downward. Prepping and draping for implantation then proceed as usual. The previous back incision is reopened and the disposable extension catheter is disconnected from the permanent in-trathecal catheter and pulled from under the patient by the circulating nurse. The intrathecal catheter is then clamped to prevent CSF loss, and the implantation proceeds in the usual manner.
Attention is then turned to the lower quadrant of the abdomen, where a 10 cm incision is made down to the underlying subcutaneous fat layer. A subcutaneous pocket large enough to admit the particular pump being used is then fashioned. Generally, if all four fingers can be admitted to the metacarpal phalangeal joints in the pocket, it is large enough. The upper side of the incision is undermined roughly as the width of the pump, or about 2.5 cm, to allow closure without tension. The eccentric location of the pocket allows the pump to be placed so that the refill port is clear of the incisional scar and easier to locate. An ideal pocket is one that will allow placement of the pump without difficulty but is tight enough to aid in preventing pump rotation. The depth of the pocket below the skin is critical for programmable pumps. A depth greater than 2.5 cm may not allow reliable telemetry. In fashioning the pocket, meticulous hemostasis is important to avoid a postoperative hematoma. At this point, the pocket is packed with an antibiotic-soaked sponge.
The catheter connecting the intrathecal catheter to the pump, or the extension catheter, is then tunneled from the pump pocket to the back incision by means of a malleable tunneling device. The author uses a cardiac pacemaker tunneling tool. Shunt tunneling tools may also be used, and a tunneling system is provided with the programmable pump, which works well. Most constant flow rate pumps come with the extension catheter connected to the pump at the factory; the catheter must be attached to the programmable pump.
A connection is now made between the extension catheter and the intrathecal catheter, using a titanium or plastic male-to-male tubing connector, usually provided with the catheter selected. This construct is covered by some type of anchoring device, which is secured to the connector with 2-0 nonabsorbable braided tie. The construct is anchored to the underlying muscle fascia in a figure 8 fashion. Do not skip the anchoring. The intrathecal catheter will migrate, usually coiling itself under the skin.
The extension catheter is now connected to the previously prepped programmable pump and secured to the pump with a 2-0 braided tie. Pumps with a previously attached catheter must be placed into the pocket at the time of catheter tunneling.
The programmable pump is now placed into the subcutaneous pocket. The Synchromed pump in its Dacron pouch may be placed without need for further suturing. Some pumps without this pouch have anchoring loops manufactured around the pump circumference, but their use may be problematic. A nonabsorbable stitch must be placed into a tissue that will not necrose. This may be the case with fat or muscle. At least two stitches are necessary to prevent rotation, and three may be necessary to prevent flipping (it happens!). This usually requires a dermal or fascial stitch, with the risk that the anchor will be painful. If this technique is used, the stitches should be placed into the pocket first, then through the pump suture loops, whereupon the pump is placed into the pocket and the sutures tied. If the pocket is carefully fashioned, even a pump lacking a Dacron pouch may be placed without suturing, especially in thin patients.
The incisions are now carefully closed. An interrupted, inverted layer of 2-0 absorbable suture in the abdomen and 3-0 absorbable suture in the back will suffice, followed by apposing the skin edges with Steri-Strips. If tension is a problem, surgical staples should be used to reinforce the closure.
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