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The relationship between the blood flow and inflow and outflow pressures was determined in PermCath, dual lumen catheters during regular hemodialyses in vivo in eight patients with average hematocrit of 38%. From the luer lock connector the catheters had an average length of 32 cm to the outflow tip and 30 cm to the inflow tip. The catheters had an internal diameter of 0.2 cm and were straight before implantation. Dialyses were performed on Fresenius 2008 D or E machines with ReadySet blood lines with an 8 mm ID pump segment and a noncollapsible arterial chamber. Pressures and blood flows were measured at pump speeds from 50 to 500 ml/min in increments of 50 ml/min with lines in normal configuration. Blood flow was measured continuously using ultrasound. The correlations between pressures and flows are not linear. The best correlations are according to the Stirling model of exponential growth category equation. Inflow pressure = -9.07-0.4865*(exp(0.0020*blood flow)-1)/0.0020 Outflow pressure = -28.14+0.5002*(exp(0.0015*blood flow)-1/0.0015 Based on these results and Poiseuille's equation a table was developed for the optimal relationship between catheter length and diameter to achieve standardized (average, low and high) blood flows regardless of the lengths of the catheters. The diameter/length relationships are based on theoretical considerations. Because resistances depend on the material and shape of the tubing, the actual measurements of flow/pressure relationships should be done once tubings of different diameters are manufactured, and final catheter design has to be based on these measurements.

Blood flow, measured by an ultrasound flowmeter, and the extent of hemolysis were assessed during a single, routine dialysis in 100 patients. Before and after the hemodialysis session, blood was drawn for measurements of haptoglobin (HPT), hemoglobin (HGB), albumin (ALB), and lactate dehydrogenase (LDH). The average values were as follows: pump speed 510 mL/ min, real blood flow 422 mL/min, arterial chamber pressure -350 mm Hg, and venous chamber pressure 279 mm Hg. Haptoglobin concentrations were higher in patients with central vein catheters compared to patients with arteriovenous access. The meaning of this finding is unclear. Mean HPT concentrations increased significantly less during hemodialysis (2.37%) than concentrations of ALB (11.3%), HGB (9.17%), and LDH (18.2%), indicating that some hemolysis is present in all dialyses. In dialyses with arterial chamber pressures more negative than -350 the median concentration of ALB (8.70%) increased significantly more than the median concentration of HGB (7.99%). This indicates significantly more hemolysis in dialyses with more negative pressures compared to those with less negative arterial chamber pressures. Median LDH increased more in dialyses with more negative prepump chamber pressures (16.19% vs 13.78%), but not significantly; however, LDH increases were significantly higher than either HGB or ALB, thus indicating significantly more hemolysis in dialyses with more negative pressures compared to those with less negative arterial chamber pressures. Erythropoietin dose was not significantly different in patients dialyzed with more or less negative arterial chamber pressures (17 645 ± 1226 U/week vs 16 308 ± 1506 U/week). We conclude that dialyses with negative arterial chamber pressures greater than -350 mm Hg cause slightly higher hemolysis than dialyses with less negative arterial chamber pressures, but this increased hemolysis is not associated with an increased requirement of erythropoietin dose. Whether this increased hemolysis is of clinical significance is uncertain.

Blood flows and recirculations with standard and reversed direction of lines were measured by chemical (urea and creatinine) and ultrasound dilution (saline) methods in 47 chronic hemodialysis patients. Thirty-seven patients had 47 dual-lumen, central vein (CV) catheters: 32 were PermCath (Quinton Instruments Company, Seattle, WA), 6 were Access Cath (MEDCOMP, Harleysville, PA), 3 were Soft Cell PC (Vas Cath, Mississauga, Ontario, Canada) and 6 were SNIJ (experimental catheters). Three of these last catheters had the tip staggered 7 mm, and three had flush tips; PermCath, Access Cath, and Soft Cell PC catheters have the tips staggered 23 to 25 mm. Forty-six catheters were implanted into the superior vena cava/right atrium, and one catheter was implanted through the left saphenous vein into the left iliac vein. The catheters were studied 1 to 31 months after implantation (median, 3.0 months). Ten patients with arteriovenous (AV) graft access were also studied. The stop-flow method was used in catheter dialysis, and the slow-flow method was used to calculate recirculations in AV access dialysis with samples for systemic blood concentrations taken from arterial line both before and after samples from the arterial and venous lines. At 500 mL/min pump speed, actual blood flow was 436+/-18 mL/min (mean+/-SD; range, 407 to 464 mL/min) with standard direction of catheter lines. At 500 mL/min pump speed, the arterial chamber pressure was -330+/-48 mm Hg (mean+/-SD; range, -380 to -225 mm Hg, and the venous chamber pressure was 259+/-48 mm Hg (mean+/-SD; range, 140 to 310 mm Hg). Arterial chamber pressure was less negative, and venous chamber pressure was less positive with SNIJ catheters, which had larger internal diameter (2.1 mm) compared with the other catheters (2.0 mm). Recirculation varied with the catheter design and the location of the catheter tip. In the catheters with tip staggered more than 20 mm and with standard line connection at pump speeds of 50 mL/min and 500 mL/min, recirculations were approximately 1 % and 5%, respectively, when measured by the chemical method. In the same catheters with reversed lines, the recirculations were approximately 5% and 27%, respectively. Inflow failure catheters with reversed lines had similar recirculation values to those of well-functioning catheters with reversed lines. In catheters with tips staggered 7 mm, and with standard connection of lines, recirculations were approximately 3% and 8%, respectively, at pump speeds of 50 and 500 mL/min. With reversed lines, at the same pump speeds, the values were 7% and 12%, respectively. In flush-tip catheters, the recirculation was higher at a 50 mL/min pump speed (approximately 17%) than at a pump speed of 500 mL/min (approximately 13%). The ultrasound dilution method usually gave lower values than the chemical methods, most likely because of overestimation of recirculation by chemical methods. At least triplicate measurements are needed because single measurements by the ultrasound dilution method are associated with substantial variation. We conclude that both currently used methods (stop flow and slow flow) of taking systemic samples for measurements of recirculation by chemical methods are flawed because of disequilibrium and recirculation at low flow.

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.(ABSTRACT TRUNCATED AT 250 WORDS)

To assess the comparative effects of hemodialysis with acetate versus bicarbonate base on left ventricular systolic function, we performed M-mode echocardiography on 36 patients prior to and immediately following 4-hr maintenance hemodialysis. Patients were initially dialyzed against either sodium acetate or sodium bicarbonate and 1 week later were dialyzed against the alternate base. The mean velocity of circumferential fiber shortening (mean Vcf, circumferences/s) was used to assess left ventricular systolic function. In patients with normal pre-dialysis mean Vcf hemodialysis with acetate produced no significant change in mean Vcf, whereas hemodialysis with bicarbonate produced a significant increase in mean Vcf. In patients with low pre-dialysis mean Vcf hemodialysis with either base produced a significant increase in mean Vcf. Mean Vcf values obtained after hemodialysis with bicarbonate were significantly higher than those obtained after hemodialysis with acetate, both in patients with normal and low pre-hemodialysis mean Vcf. We conclude that hemodialysis with bicarbonate produces a comparatively greater improvement in left ventricular systolic function than hemodialysis with acetate.