Postprocedural aspiration test to predict adequacy of dialysis following tunneled catheter placement

The objective of the study was to determine if a timed aspiration technique with a 20-ml syringe can be used to predict adequacy of blood flow in tunneled dialysis catheters. Sixteen patients referred for de novo placement or manipulation of failing tunneled hemodialysis catheters had the time it takes to fill a 20-ml syringe with the plunger fully withdrawn measured to the nearest tenth of a second. These measurements were correlated with flow rates recorded in dialysis just prior to (if failed catheter) and in the following dialysis session with adequacy determined as at least 300 ml/min. Syringe-filling time (22 catheters in 16 patients) was plotted against adequacy of dialysis. The mean time to fill a 20-ml syringe was 2.2 sec, with a range of 1.0-4.7 sec. The mean time to fill syringes for catheters with adequate dialysis was 1.7 +/- 0.5 sec, and for inadequate catheters, it was 2.8 +/- 0.8 sec. These differences are statistically significant (p < 0.001). Using a filling time of greater than or equal to 2 sec as a threshold gives the highest sensitivity (100%) for predicting inadequate dialysis while maintaining high specificity (75%). To achieve a specificity of 100%, a 3-sec cutoff would be necessary, but would lead to a sensitivity of only 20%. A simple and objective aspiration technique can be performed at the time of tunneled dialysis catheter placement/manipulation to reasonably predict adequacy of subsequent dialysis.