Vascular Access

To allow continuous blood processing for PBSC collection two ports of vascular access are necessary. In adults this requires two antecubital lines. In 5-10 % of adults and most children, percutaneous antecubital large-bore access is not possible and a pheresis catheter is used instead. A veno-arterial approach, utilizing an arterial line to draw blood and a conven tional venous catheter to return it to the patient, has also been described (Takaue et al. 1995). Although there are many configurations, a pheresis catheter is generally a two-lumen catheter with offset proximal and distal ports and side holes along the tip of the catheter. This offset configuration minimizes mixing of processed and unprocessed blood and maximizes the efficiency of the collection. Since apheresis machines can draw 70 cc per min, conventional Broviac-type catheters can be difficult for patients <35 kg,be-cause the lumen collapses under the negative pressure used to draw blood at 2 ml/kg min-1. A pheresis catheter is designed to allow faster draw rates using a combination of larger lumen size, shorter catheter length, and stiffer walls.

Pheresis catheters are available both for temporary and tunneled insertion. Small patients (approx. 10-30 kg) may require an 8 F cuffed tunneled pheresis catheter (MedComp). Smaller patients may require femoral line placement. The concern in smaller patients is threefold: (a) the risk of partial or complete vessel occlusion with the catheter; (b) the risk of vessel erosion and perforation, which may be greater with stiffer catheters in small vessels (Welch et al. 1997); and (c) the difficulty in placing an offset catheter in a short vessel where, if the proximal port is in adequate position, the distal port may be too far advanced. Femoral catheters are short, allowing faster collect rates for a given diameter; however, a patient with a percutaneous nontunneled femoral catheter cannot walk, necessitating admission to the hospital for what is otherwise an outpatient procedure. Also, the perceived risk of complication (especially infection) with a femoral catheter is higher (Merrer et al. 2001). For both of these reasons, femoral catheters are generally only placed temporarily, except in unusual circumstances (Chow et al. 2001). Another approach used at some institutions is to place a single lumen 7F Broviac-type central venous catheter on the opposite side of the patient's existing double lumen catheter. The single lumen line is then used as the draw line and the smaller double lumen catheter is used as the return line.

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