Preoperative Mapping Using a Catheter Sample
Figure 1. Schematic of a supine patient showing the manner in which the catheter insertion site and deep cuff location are selected in order to achieve optimal pelvic position of coiled- and straight-tip catheters.
The most appropriate choice of catheter is the one that produces the best balance of pelvic location of the catheter tip, exit-site easily visible to the patient, and can be inserted through the abdominal wall with the least amount of tubing stress. The catheter insertion site is the fulcrum of this best balance and will determine the pelvic position of the catheter tip and the range of reachable exit-sites. Therefore, catheter selection begins with determination of the insertion site. With the patient in the supine position, the insertion site for each style and size of catheter is determined by marking the upper border of the deep cuff in the paramedian plane when the upper border of the catheter coil is aligned with the upper border of the pubic symphysis (Figure 1). For straight-tip catheters, a point 5 cm from the end is aligned with the upper border of the pubic symphysis. If a straight-tip catheter design is preferred, choose a version that provides no more than 15 cm of length below the deep cuff to avoid having excess tubing crowded in the pelvis. During the catheter placement procedure, the deep cuff is implanted within the rectus muscle (or just below) at the level of the insertion incision. Using this convention to determine the insertion site will prevent the catheter tip from being implanted too low in the pelvis, producing pressure or poking discomfort, early termination of dialysate outflow, and severe end of drain pain.5
After determining the catheter insertion site, the subcutaneous tunnel path and exit-site location for catheters with a preformed swan neck bend simply follows the configuration of the tubing, marking the skin exit-site 2–3 cm beyond the superficial cuff. Catheters with a straight intercuff segment should assume a gentle arc in the subcutaneous tissues to produce more of a laterally directed exit-site. To enable a gentle arc bend of the straight intercuff tubing segment, choose a catheter version with 5 to 6 cm between the Dacron cuffs. Illustrated in Figure 2 is a convenient 3-step algorithm for catheters with a straight intercuff segment to design a laterally directed tunnel and exit-site that minimizes creation of excessive tubing stress and shape-memory resiliency forces that can lead to catheter tip migration and superficial cuff extrusion. The inherent properties of this algorithm prevent the superficial cuff from coming any closer than 2 cm of the exit-site, even use in the worst-case scenario of tube straightening.
Figure 2. Three-step algorithm for lateral tunnel track and exit-site design.
Step 1: scribe arc from vertical to horizontal plane using catheter as compass from point 2 cm external of superficial cuff.
Step 2: mark exit-site at junction of medial 2/3 and lateral 1/3 of arc.
Step 3: indicate tunnel track shape by bending catheter over from point 4 cm external of superficial cuff to exitsite.
(Crabtree JH. Selected best demonstrated practices in peritoneal dialysis access. Kidney Int Suppl. 2006;103:S27–37. Figure 10)
If the catheter needs to be bent more than a laterally directed exit-site, a catheter with a preformed swan neck bend should be used instead to eliminate these excessive forces. Upwardly directed exit-sites should be avoided to prevent pooling of cutaneous bacteria and debris, perspiration, and shower water in the exit sinus, predisposing the patient to exit-site and tunnel infection.
After mapping exit-site locations, the patient assumes a sitting position and the marked exit-sites are checked to see which is best visualized by the patient and does not conflict with the belt line, skin creases, or apices of bulging skin folds. If none of the marked exit-sites for the standard abdominal catheters are satisfactory, the patient is then considered for an extended catheter to produce an upper abdominal or presternal exit-site location.