Continuous Hemodialysis

Some of the renal replacement therapies listed in Table 6.2 incorporate continuous hemodialysis or a combination of continuous hemofiltration and hemodialysis. Continuous hemodialysis differs importantly from conventional intermittent hemodialysis in that the flow rate of dialysate is much lower than is countercurrent blood flow through the dialyzer. As a result/ concentrations of many solutes in dialysate leaving the dialyzer (Cd) will have nearly equilibrated with their plasma concentrations in blood entering the dialyzer (Cp) (16/31). The extent to which this equilibration is complete is referred to as the dialysate saturation (Sd) and is calculated as the following ratio  

In contrast with intermittent hemodialysis in which dialyzer blood flow is rate limiting/ diffusive drug clearance during continuous renal replacement therapy is limited by dialysate flow (Qd)/ which typically is only 25 mL/min. Accordingly/ diffusive drug clearance (CLd) is calculated from the equation  

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Hemofiltration is a prominent feature of many continuous renal replacement therapies (Table 6.2). How-ever continuous hemodialysis can also be employed to accelerate solute removal (16). The contribution of both processes to extracorporeal drug clearance will be considered separately in the context of continuous renal replacement therapy. 

Sigler MH, Teehan BP, Van Valceknburgh D. Solute transport in continuous hemodialysis A new treatment for acute renal failure. Kidney Int 1987 32 562-71. 

A 36-year-old long-distance truck driver took 200 ml of ethylene glycol in a suicide attempt (32). He vomited, lost consciousness, and had miosis and external ophthalmoplegia. There was a severe metabolic acidosis with a wide anion gap and many crystals in the urinary sediment. Acute oliguric renal failure required continuous hemodialysis for 6 days. A CT scan of the brain showed low-density areas in the bilateral basal ganglia, midbrain, and pons. A renal biopsy showed tubular oxalate deposits. He gradually recovered within 36 days. 

Gastric lavage should be carried out immediately if oral consumption is suspected. In order to hasten intestinal elimination charcoal tablets should be administered at 4-hr intervals with sodium sulfate as laxative. To activate the antimony the chelating agent Sulfactin must be administered intramuscularly and also about every 4 hr. Chelated antimony is excreted renally and is readily dialyzed. Hence continuous hemodialysis can be carried out if necessary. The administration of Sulfactin must be continued throughout the whole dialysis. The intravenous administration of lasix with a balanced substitution of electrolyte solutions to force diuresis is also promising in cases of very high levels of Sb intoxication [33]. 

CWH, continuous venovenous hemofiltration CWHD, continuous venovenous hemodialysis CVVHDF, continuous venovenous hemodiafil-tration. 

With either type of dialysis, studies suggest that recovery of renal function is decreased in ARF patients who undergo dialysis compared with those not requiring dialysis. Decreased recovery of renal function may be due to hemodialysis-induced hypotension causing additional ischemic injury to the kidney. Also, exposure of a patient s blood to bioincompatible dialysis membranes (cuprophane or cellulose acetate) results in complement and leukocyte activation which can lead to neutrophil infiltration into the kidney and release of vasoconstrictive substances that can prolong renal dysfunction.26 Synthetic membranes composed of substances such as polysulfone, polyacrylonitrile, and polymethylmethacrylate are considered to be more biocompatible and would be less likely to activate complement. Synthetic membranes are generally more expensive than cellulose-based membranes. Several recent meta-analyses found no difference in mortality between biocompatible and bioincompatible membranes. Whether biocompatible membranes lead to better patient outcomes continues to be debated. 

Peritoneal dialysis (PD) utilizes similar principles as hemodialysis in that blood is exposed to a semipermeable membrane against which a physiologic solution is placed. In the case of PD, however, the semipermeable membrane is the peritoneal membrane, and a sterile dialysate is instilled into the peritoneal cavity. The peritoneal membrane is composed of a continuous single layer of mesothelial cells that covers the abdominal and pelvic walls on one side of the peritoneal cavity, and the visceral organs, including the GI tract, liver, spleen, and diaphragm on the other side. The mesothelial cells are covered by microvilli that increase the surface area of the peritoneal membrane to approximate body surface area (1 to 2 m2). 

Renal failure receiving intermittent hemodialysis (IHD) Renal failure receiving continuous ambulatory peritoneal 1-1-13 g/kg... 

Renal replacement therapy (RRT), such as hemodialysis and peritoneal dialysis, maintains fluid and electrolyte balance while removing waste products. See Table 75-4 for indications for RRT in ARF. Intermittent and continuous options have different advantages (and disadvantages) but, after correcting for severity of illness, have similar outcomes. Consequently, hybrid approaches (e.g., sustained low-efficiency dialysis and extended daily dialysis) are being developed to provide the advantages of both. 

Elevated Lp(a) levels were reported in patients with various forms of renal failure and under treatments like hemodialysis and continuous ambulatory peritoneal dialysis (CAPD) (B28, Cll, H5, K2, K5, M34, P4, P6, S8, T2, W8). After renal transplantation and CAPD, Lp(a) concentrations are reported to de-... 

Renal function impairment Because daptomycin is eliminated primarily by the kidney, a dosage modification is recommended for patients with creatinine clearance (Ccr) less than 30 mL/min, including patients receiving hemodialysis or continuous ambulatory peritoneal dialysis (CARD). When possible, administer daptomycin following hemodialysis on hemodialysis days. 

Metabolism/Excretion - In the first 24 hours, approximately 75% of a dose is excreted in urine by glomerular filtration. Elimination half-life is 4 to 6 hours in adults and 2 to 3 hours in children. About 60% of an intraperitoneal dose administered during peritoneal dialysis is absorbed systemically in 6 hours. Accumulation occurs in renal failure. Serum half-life in anephric patients is approximately 7.5 days. Vancomycin is not significantly removed by hemodialysis or continuous ambulatory peritoneal dialysis, although there have been reports of increased clearance with hemoperfusion and hemofiltration. 

Peritoneal dialysis Supplemental doses of valacyclovir should not be required following chronic ambulatory peritoneal dialysis (CARD) or continuous arteriovenous hemofiltration/hemodialysis (CAVHD). 

In continuous ambulatory peritoneal dialysis (CAP )), approximately 21 of dialysate solution is infused into the patient s peritoneal cavity, and is exchanged with new dialysate about four times each day. The patient need not stay in bed, as with ordinary hemodialysis, but it is difficult to continue CAPD for many years due to the formation of peritoneal adhesions. 

Peritoneal Dialyis There is no information specific to administration of VALTREX in patients receiving peritoneal dialysis. The effect of chronic ambulatory peritoneal dialysis (CARD) and continuous arteriovenous hemofiltration/dialysis (CAVHD) on acyclovir pharmacokinetics has been studied. The removal of acyclovir after CARD and CAVHD is less pronounced than with hemodialysis, and the pharmacokinetic parameters closely resemble those observed in patients with ESRD not receiving hemodialysis. Therefore, supplemental doses of VALTREX should not be required following CARD or CAVHD. 

Kanakiriya S, De Chazal I, Nath KA, Haugen EN, Albright RC, Juncos LA. Iodine toxicity treated with hemodialysis and continuous venovenous hemodiafiltration. Am J Kidney Dis 2003 41 702-8. 

Five patients with metformin-associated severe lactic acidosis, seen between 1 September 1998 and 31 May 2001, have been reported (58). Two had attempted suicide. All had severe metabolic acidosis with a high anion gap and raised blood lactate concentrations. Four developed profound hypotension and three had acute respiratory failure. Three had normal preceding renal function. Three required conventional hemodialysis and two continuous renal replacement therapy. 

The results of hemodialysis in biguanide-induced lactic acidosis are variable. Metformin and buformin are dialy-sable, but phenformin is poorly eliminated. Successful continuous venovenous hemofiltration has been reported (81). 

A 75-year-old-man taking simvastatin 80 mg/day and diltiazem 240 mg/day developed extreme weakness and diffuse muscle pain. All drugs were withdrawn and he underwent hemodialysis. Within 3 weeks his muscle pain disappeared and he regained function in his legs. The activities of creatine kinase and transaminases gradually returned to normal, but he continued to need hemodialysis. 

A 64-year-old African-American man developed worsening renal insufficiency, raised creatine kinase activity, diffuse muscle pain, and severe muscle weakness. He had been taking simvastatin for about 6 months and clarithromycin for sinusitis for about 3 weeks. He was treated aggressively with intravenous hydration, sodium bicarbonate, and hemodialysis. A muscle biopsy showed necrotizing myopathy secondary to a toxin. He continued to receive intermittent hemodialysis until he died from infectious complications 3 months after admission. 

In contrast to hemodialysis that uses ultrafiltration membranes, plasma separation (also called plasmapheresis) requires microfiltration membranes with a pore size from 0.2 to 0.6 pm, in order to transmit all proteins and lipids, including LDL cholesterol (2000kDa) and retain completely platelets (2 pm diameter), red blood cells (8 pm diameter) and white blood cells. Thus, membrane plasmapheresis can yield high-quality platelet-free plasma and red cells can be either continuously returned to the donor or saved in another bag for blood transfusion. But it is important, in the case of plasma collection from donors, to minimize the membrane area, in order to reduce the cost of disposable hollow-fiber filters and to avoid the risk of hemolysis (free hemoglobin release) due to RBC damage by contact at the membrane if the pressure difference across the membrane is too high. 

A 52-year-old man with a serum lithium concentration of 4.58 mmol/1 had sinus node dysfunction with multiple atrial extra beats and an intraventricular conduction delay, which normalized following hemodialysis (132). Two patients, a 58-year-old woman and a 74-year-old woman, developed sick sinus syndrome while taking lithium but were able to continue taking it after pacemaker implantation (135,136). 

Hemodialysis (383,552,553), sometimes with additional continuous venovenous hemofiltration dialysis (554,555), continues to be described as a successful intervention for lithium poisoning. Peritoneal dialysis is a far less efficient way to clear lithium from the body. One patient treated in this way had permanent neurological abnormalities and another died a third toxic patient who also had diabetic ketoacidosis died after treatment with hydration and insulin (556). On the other hand, a 51-year-old woman who took 50 slow-release lithium carbonate tablets (450 mg) had a serum lithium concentration of 10.6 mmol/1 13 hours later, but no evidence of neurotoxicity or nephrotoxicity. She was treated conservatively with intravenous fluids and recovered fully (557). Acute lithium overdose is often better tolerated than chronic intoxication. 

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