Resistance of vascular access catheters for continuous renal replacement therapy: An ex vivo evaluation

Aim: To assess the resistance posed by double-lumen vascular access dialysis catheters at low and high blood flow. Design: Controlled ex vivo study Setting: ICU Laboratory of tertiary hospital. Subjects: Eleven proprietary vascular access catheters for continuous renal replacement therapy. Methods: Heparinized spent red cells diluted in polygeline solution were pumped using the Aquarius hemofiltration machine (Edwards Life Sciences, Sydney, NSW Australia) and its standard circuit through several vascular access catheters. Blood flow was increased and then decreased in steps of 50 ml/min (50, 150, 200, 250 and 300 ml/min) while catheter outflow and inflow pressures were recorded. The pressure-flow relationship (hydraulic resistance) of each catheter was then calculated. Study catheters were divided into two groups according to their internal diameter (large gauge vs. smaller gauge) or length (long or short). Hydraulic resistances were compared between the groups. Results: Different double lumen catheters posed clearly different resistances to flow. For all groups of catheters, there was a linear relationship between pressure and flow. No statistically significant difference between short and long catheters could be demonstrated (p=0.715). On the other hand, larger gauge catheters (13 Fr or greater) had significantly lower resistances than smaller gauge (< 13 Fr) catheters (p=0.0062). Furthermore, all larger gauge catheters had resistances lower than 0.430 mmHg/ml/min, while all smaller gauge catheters had resistances greater than 0.490 mmHg/ml/min. Conclusions: Commercial double-lumen dialysis catheters have variable resistance to blood flow under standard ex vivo conditions. Although both length and internal diameter varied, internal diameter had a dominant effect on resistance. This information might be useful to clinicians in guiding their choice of catheters for clinical use. (Int J Artif Organs 2008; 31: 905-9)