Blood recirculation in intravenous catheters for hemodialysis

Long-term i.v. catheters for hemodialysis have the outflow tip extending approximately 2 to 3 cm beyond the inflow tip to prevent blood recirculation during dialysis; however, the lumens are frequently reversed because of inflow failure (i.e., inadequate flow when the inflow lumen is used for blood inflow into the dialyzer). Blood recirculation with reversed lumens (outflow lumen used for blood inflow) in inflow failure catheters and with standard and reversed lumens in well-functioning catheters was measured. Recirculation was measured at a blood flow of 300 mL/min. Systemic blood samples were taken after blood flow was slowed to 50 mL/min. Blood recirculation was calculated as a percentage of the difference between systemic and inflow lumen solute concentrations divided by the difference between systemic and outflow lumen solute concentrations. For each catheter, the recirculation values were calculated separately for urea and creatinine. Average recirculation as measured by both solutes was also calculated. Blood recirculations with standard lumens of well-functioning catheters, reversed lumens of well-functioning catheters, and reversed lumens of inflow failure catheters were 2.09 +/- 1.95, 13.58 +/- 9.87, and 7.10 +/- 5.12 (mean +/- SD), respectively. Whereas recirculation with standard lumens of well-functioning catheters is negligible, reversal of lumens causes considerable recirculation. Recirculation in inflow failure catheters with reversed lumens is significantly less than that with reversed lumens of well-functioning catheters. It was proposed that a blood clot attached at and/or immediately distal to the inflow lumen may disperse outflowing blood and diminish recirculation in inflow failure catheters.