Evaluation of blood recirculation in catheters for haemodialysis and its relation to blood circuit pressures.

Abstract

The objectives of this study were to evaluate the degree of blood recirculation (REC) in venous catheters for dual lumen haemodialysis, and its relation to the drop in arterial line pressure and return venous pressure during haemodialysis. A total of 25 catheters were evaluated (15 temporary 15 cm catheters, and 10 permanent tunnelled 32 cm catheters). REC was calculated using a blood temperature monitor. With blood flow stabilised at 250 ml/min,the session was initiated and the following was determined: real blood flow, drop in arterial line pressure (pre-pump pressure), positive pressure and blood recirculation. Mean blood recirculation in the total of catheters was 6.4 +/- 3%, mean real blood flow was 230 +/- 9 ml/min. Mean blood pressure was -146 +/- 52 mmHG. Mean positive pressure was 127 +/- 47 mmHG. A strong correlation was found between real flow and arterial pressure (r = 0.79, p < 0.01), and between arterial pressure and blood recirculation (r = -0.57, p < 0.01). Comparing the variables studied, a lower degree of REC (5.2+/-2 vs. 8.5+/-3, p < 0.01), a higher real blood flow (234 +/- 7 vs. 223 +/- 7, p < 0.01) and a lower drop in arterial pressure (-127 +/- 49 vs. -180 +/- 40, p < 0.05) were found in temporary catheters than in permanent catheters. No differences were observed in positive pressure. As a conclusion, these results suggest that blood recirculation is lower in temporary catheters than in permanent tunnelled catheters. This is related to a lower drop in pre-pump blood pressure and a higher real blood flow. However, positive pressure does not seem to influence the degree of blood recirculation in venous dual lumen catheters for haemodialysis.