VALIDATION OF A REVISED SLOW-STOP FLOW RECIRCULATION METHOD

Slow flow/stop flow methods have replaced the three needle technique a s methods of choice for measuring recirculation. However, the time del ay after reducing brood flow may affect the BUN in the systemic (slow flow/stop flow arterial line) sample and therefore limit the accuracy of this methodology. It has been observed that recirculation does not occur in a properly cannulated access unless the access blood flow rat e is less than the dialyzer blood flow rate (BFR). This suggests that the systemic sample could be obtained at a higher than usual blood pum p rate. We studied 50 patients and compared a revised slow-stop flow ( S/SF) recirculation technique in which the systemic sample was drawn a fter the blood pump rate was reduced to 120 ml/min for 10 seconds and then stopped, to a non-urea based method that utilized indicator veloc ity dilution (IVDM). Seven patients were found to have recirculation b y IVDM; all had recirculation by S/SF of more than 10% (minimum 16.7%) and an access BFR that was less than the dialyzer BFR. In the 43 pati ents without recirculation by IVDM, the mean recirculation by S/SF was 1.9 +/- 3.2% (mean +/- SD). Five patients without recirculation by IV DM had more than 5% recirculation by S/SF (range, 5.9 to 8.3%). Althou gh there was a small systematic tendency to overestimate recirculation , this modified urea based method was still able to detect recirculati on with good reliability. Single values above 30% are highly likely to indicate the presence of true recirculation. Repeated values over 5% are also likely to be significant, indicating the presence of true rec irculation and its clinical correlate, marginal access blood flow.