Simplified method of hemofiltration in ventricular assist device patients

Hypervolemia frequently complicates the management of ventricular assist device (VAD) patients as a result of increased intravenous fluid administration and concomitant renal dysfunction. Although acute hemodialysis (AHD) can be used to treat such patients, it requires additional equipment, vascular access cannulations, and personnel. Moreover, hypotension during AHD may occur as a result of rapid shifts in intravascular volume. From January 1987 to March 1988, we treated nine selected VAD patients who had hypervolemia and acute renal failure with a simplified hemofiltration technique. A continuous arteriovenous hemofiltration (CAVH) cartridge was connected from the outflow circuit of a centrifugal blood pump to a large-bore central venous catheter. With CAVH, gradual removal of 272 cc/hour of ultrafiltrate was accomplished for periods up to 241 hours. No episodes of hypotension, thromboembolism, or other deleterious effects occurred. In our series, the CAVH technique was effective in treating hypervolemia in selected VAD patients.

Temperature dependence of macromolecular sieving across plasma fractionating membranes

The temperature dependence of macromolecular sieving coefficients (S) across a plasma fractionating membrane due to changes in the intrinsic process of membrane filtration was determined using dextrans as test macromolecules. Sieving coefficients were determined in an in vitro test circuit as a function of time, temperature, flow conditions, and plasma protein exposure. Sieving coefficients for albumin, gamma G immunoglobulin (IgG), and dextrans using normal human plasma as the test solution were comparable for dextrans and proteins of equivalent molecular size, independent of time after 15 min, lower at 8 degrees than at 37 degrees C, and higher at lower filtration flow rates. At 8 degrees C and high filtration flow rates, S for albumin and IgG also increased with increasing perfusate flow rate. Dextran S using a protein-free test solution before exposure to plasma were higher than those determined from plasma, and were independent of temperature. Dextran S from a protein-free test solution after exposure to plasma were similar to those determined from plasma at 37 degrees C, but higher than those determined from plasma at 8 degrees C. We conclude that sieving coefficients across plasma fractionating membranes can be altered by temperature due to changes in the process of membrane filtration. The present observations suggest that at low temperature a polarized layer or gel becomes a discriminating solute transport barrier.

Blood-dialysate equilibration during continuous arteriovenous hemodialysis

In order to determine the degree to which blood and dialysate achieve equilibration of urea concentration during continuous arteriovenous hemodialysis (CAVHD), CAVHD circuits employing the Hospal AN69S dialyzer were perfused with bovine blood (85 to 90 ml/min, hematocrit 28%) containing 50 mg/dl of urea in the presence of countercurrent dialysate flowing at 10, 20, or 30 ml/min. The circuits were constructed and perfusion pressure (66 mmHg) set to yield a near zero net ultrafiltration rate. Urea clearances were measured and found to approximate the dialysate inflow rate, Qd, up to about 15 ml/min. At higher dialysate flow rates, equilibration was incomplete so that urea clearance was 24.7 +/- 0.5 (mean +/- SE) ml/min when Qd was 30 ml/min. A simplified model of urea transport in the dialyzer successfully simulated the data.

Treatment of acute renal failure in an infant by continuous arteriovenous hemodialysis

Continuous arteriovenous hemodialysis (CAVHD) was performed in a critically ill oliguric infant with progressive uremia using a miniature Amicon hemofilter. Modification was made in the filter system by circulating 2.5% Dianeal peritoneal dialysis fluid into the second port of the ultrafiltrate compartment to enable the filter to function by dialysis too (CAVHD). In comparison with continuous arteriovenous hemofiltration (CAVH), CAVHD provided superior urea clearance and adequate fluid removal, allowing the simultaneous administration of parenteral nutrition. The higher solute clearances in CAVHD make the technique superior to CAVH for renal replacement therapy in critically ill infants.

Comparison of four different short dialysis techniques

The goal of shortening dialysis treatment time has stimulated the development of new, highly efficient dialytic strategies. In this study the Authors compared four different short dialysis treatments in terms of efficiency, clinical tolerance, technological investment and costs: 1) Rapid bicarbonate dialysis with 1.5 sq.m. cuprophane membrane; 2) High flux biofiltration with 1.2 sq.m. AN69S hollow fiber membrane; 3) Hemodiafiltration with 1.2-1.9. sq.m. polysulphonic hollow fiber hemodiafilters, and 4) High flux hemodiafiltration with two serial hemodiafilters with AN69s membrane (total 2.4 sq.m.). Hydraulic properties and solute clearances at different blood flows (300-500 ml/min) were tested for each technique. Once the optimal operative level was established three patients were treated with each technique for at least six months. Since BUN clearance averaged 310 ml/min, the treatment duration varied from 120 to 180 min/session with KT/V always higher than 1. The average protein catabolic rate was 0.9 g/kg/24h. Clinical tolerance was generally good, slightly better in treatments with a high convective component. Despite the greater efficiency of treatment No. 4, the technological requirements and costs are such that the others are currently more feasible and acceptable in clinical routine. The study demonstrates that reduction of dialysis treatment time is possible in all centres in a selected population with adequate blood access. Treatment No. 1 can even be performed with standard equipment and cuprophan membranes, while bicarbonate in the dialysate is mandatory. The real limit to shortening treatment time seems to be related to the maximal rate of ultrafiltration achievable in the patient during dialysis.

Evaluation of beta 2-microglobulin removal with high-performance hemodiafiltration

Several lines of evidence suggest that beta 2-microglobulin (beta 2M) accumulation in long-term hemodialysis (HD) patients results in so-called dialysis-associated amyloidosis (DAA), which is clinically manifested by carpal tunnel syndrome, osteoarthropathy, and the other organ involvements. For the purpose of preventing the beta 2M accumulation, the efficiency of beta 2M removal during (HPM), hemofiltration (HF), HD, and charcoal hemodiafiltration (HDF) with high-performance membranes (HPM), hemofiltration (HF), HD, and charcoal hemoperfusion was evaluated. Among 27 patients treated with these methods, significant beta 2M removal was noted in HDF with HPM and HD with polyacrylonitril (PAN) membrane. However, treatment of HDF with HPM for more than 6 months caused no remarkable improvement in clinical symptoms of patients, and serum beta 2M levels decreased in only two out of 15 patients. These results imply that beta 2M might be most effectively removed by HDF with HPM and HD with PAN membrane, but further long-term studies will be necessary to conclude whether these procedures could become successful therapeutic regimen for DAA.

Vascular access for continuous arteriovenous hemofiltration in infants and young children

The blood flow through the hemofilter device is the key point for ultrafiltrate production during continuous arteriovenous hemofiltration. It mainly depends on arteriovenous pressure gradient and vascular access, which is the major problem for arteriovenous hemofiltration in infants and small children. In infants, we inserted short 18-20 gauge catheters into the radial or brachial artery and the internal jugular vein and achieved mean blood flow and ultrafiltration rates of 6.5 +/- 2.2 and 1.3 +/- 0.3 ml/min, respectively. In small children, we placed 4 or 5 French catheters into the femoral vessels, and achieved mean blood flow and ultrafiltration rates ranging from 18.5 to 63.6 and 1.9 to 6.9 ml/min, respectively. The only catheter-related complication was a femoral artery thrombosis, which needed surgical revision. These results show that vascular access for arteriovenous hemofiltration in infants and small children provides sufficient blood flow through the device for ultrafiltrate production.

Hemodynamic changes during acetate dialysis, bicarbonate dialysis and hemofiltration

Twenty uremic patients submitted to three different dialytic procedures (6 patients to acetate dialysis, 8 patients to bicarbonate dialysis, 6 patients to hemofiltration) were monitored in respect to the hemodynamic parameters recorded with a thermistor Swan-Ganz catheter. During acetate dialysis there was an increment of cardiac index (CI) up to positive values (+4.8%), while resistance index (RI) decreased progressively until it reached -16.5%. During bicarbonate dialysis CI, after an initial fall, remained constant and RI increased (+8.6%). During hemofiltration CI decreased constantly throughout the entire procedure while RI increased until +12.9%. We concluded that during diffusive transport the buffer used plays an important role in determining hemodynamic responses to fluid removal; during convective transport vascular resistance increases in spite of acetate.

Suction-supported continuous arteriovenous hemofiltration in children

Spontaneous continuous arteriovenous hemofiltration (CAVH) may fail to control azotemia in small patients with renal failure due to poor blood flow. To produce adequate ultrafiltrate a continuous negative pressure was added to the ultrafiltrate line. Two hemofilter systems of different membrane and surface area were used. Suction support approximately doubled ultrafiltration rate in both hemofilters. No side effects such as severe hypotonia or early hemofilter clotting occurred. Added suction can serve as a useful support of spontaneous CAVH in children with renal failure and too poor a blood flow to control azotemia.

Search for optimizing dialysis therapy. I. Acute effects of hemodiafiltration with a highly permeable membrane and a large dose of convection and diffusion

Based on the concept that an optimisation of dialysis therapy might be achieved by increasing the removal of small metabolic substances as well as low molecular weight proteins, hemodialfiltration (HDF) was modified. In 9 ESRD patients, HDF was performed acutely for 4 h, where 60 liters of substitution fluid were infused per patient. Two polysulphone F60 membranes in line were used as hemodialfilters. As compared to conventional hemodialysis (HD), performed with a cuprophane dialyser, HDF resulted in higher extraction indices for small solutes assessed by HPLC. Due to the large amount of convection applied, HDF was followed by significant decreases of low molecular weight proteins ranging from 9.5 kdaltons (iPTH, p less than 0.01) to 17 kdaltons (myoglobin, p less than 0.01). Analysis of the protein pattern of the serum revealed a nonlinear function in the decrease of plasma proteins after HDF. It is concluded that even though the detoxification efficacy of the described HDF method is by far superior to conventional HD in quality and quantity, the efficacy is still far from that of excretory renal function. Thus, to further improve efficacy with respect to the catabolic renal function for low molecular weight proteins, membranes for HDF or hemofiltration barriers but should surpass the sieving properties of the glomerulus in the low molecular protein range.

Continuous arteriovenous hemofiltration--a new treatment in hypercalcemic crisis

A case of hypercalcemic crisis, with accompanying anuria, due to recurrence of a parathyroid carcinoma and unresponsive to conventional medical treatment, was treated with continuous arteriovenous hemofiltration (CAVH). A maximum of 24 mmol of calcium was removed per 24 h by CAVH and serum calcium was temporarily normalized. Rising values during continued treatment necessitated acute parathyroidectomy. CAVH may represent a new treatment in hypercalcemic crisis, unresponsive to medical treatment.