Metabolic Complications of Chronic Kidney Failure and Hemodialysis

Chronic kidney disease is a very real and growing problem, as indicated by demographic trends. The total number of treated patients has markedly increased during the last 30 years, and chronic kidney disease currently affects approximately 19 million adult Americans, with an incidence that is still increasing (Snyder & Pendergraph, 2005). This trend is caused by a growing percentage of elderly people in the population as well as by technical progress and broader availability of dialysis therapy. An increasing number of diabetic patients is a further important factor. Chronic kidney disease is characterized by progressive deterioration of kidney function, which develops eventually into a terminal stage of chronic kidney failure. Chronic kidney failure has traditionally been categorized as mild, moderate, or severe. Other poorly defined terms like uremia and end-stage renal disease have commonly been applied. During the last few years, an international consensus has emerged categorizing chronic kidney failure into 5 stages according to the glomerular filtration rate (GFR) and presence of signs of kidney damage: stage 1: GFR > 90 ml/min and signs of kidney damage; stage 2: GFR = 60–89 ml/min and signs of kidney damage; stage 3: GFR = 30–59 ml/min; stage 4: GFR = 15–29 ml/min; and stage 5: GFR < 15 ml/min (Levey et al., 2005). RIFLE (from Risk, Injury, Failure, Loss, End Stage) is a modern classification of acute renal failure and it is noteworthy here (Van Biesen et al., 2006). Stage 5 of chronic kidney failure represents the total inability of kidneys to maintain homeostasis, and this metabolic state is without treatment incompatible with life. Thus, at this stage, it is necessary to use methods that substitute for kidney function to ensure patient survival; these methods include hemodialysis, peritoneal dialysis, and other extracorporeal purifying procedures, or kidney transplantation. Chronic kidney failure is associated with many kinds of metabolic changes caused by the kidney disease itself and also attributable to dialysis treatment. Phenomena such as accumulation or deficit of various substances and dysregulation of metabolic pathways participate and combine in the pathogenesis of these changes. In the process of accumulation, decreased urinary excretion plays a crucial role and leads to retention of metabolites in the organism (e.g., creatinine, urea, electrolytes, water, substances with middle molecular weight such as beta-2 microglobulin and other). The increased formation of metabolites through catabolic processes and alternative metabolic pathways also wields an influence. Regular dialysis treatment partly decreases this accumulation but cannot avert