Page 164 - Biomedical Engineering and Design Handbook Volume 2, Applications

CHAPTER 5

DESIGN OF ARTIFICIAL KIDNEYS

Narender P. Reddy
University of Akron, Akron, Ohio

5.1 INTRODUCTION 143 5.5 TREATMENT PROTOCOL AND
5.2 REQUIREMENTS OF AN ARTIFICIAL ADEQUACY OF DIALYSIS 153
KIDNEY 144 5.6 BIOENGINEERED ARTIFICIAL KIDNEY 157
5.3 LOW FLUX VERSUS HIGH FLUX 5.7 CONCLUSION 158
DIALYSIS 147 REFERENCES 158
5.4 MEMBRANES FOR DIALYSIS 149

5.1 INTRODUCTION

The human kidney constitutes one of the most vital and sensitive organs, and represents the most com-
plex mass transfer and excretory mechanisms of the body. In addition to excreting urea and other meta-
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bolic waste products, the kidneys regulate the body fluid volume, the ionic content (Na , C , K ), and
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the acid base balance through the excretion of water, excess ions, and elimination of H and HCO . Also,
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the kidney performs several nonexcretory functions, including the production of numerous hormones. 1
Significant failure of the kidney function often results in quick buildup of urea and other metabolic
waste, which in turn leads to cessation of vital metabolic reactions. In acute renal failure, complete
recovery is expected in few days or weeks. Chronic renal failure, on the other hand, can lead to irrevo-
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cable loss of kidney function. Chronic renal failure can result from a number of etiologies, including
chronic infection, glomerular nephritis, renal ischemia (inhibition of blood flow), reflex nephropathy,
diabetes mellitus, etc. Renal failure leads to uremia, and uremia leads to weakness, lethargy, fuzzy con-
sciousness, vomiting, and may sometimes lead to seizure and coma. The artificial kidney device presents
a life-saving opportunity for patients with chronic renal failure.
In the natural kidney, most components of the blood, except blood cells and proteins, are first
filtered out using ultrafiltration, and then the essential nutrients (glucose, amino acids, etc.) and the
required amounts of electrolytes (Na, K, Cl, HCO , Ca, Mg, etc.) and water are reabsorbed through
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either passive, active, or facilitated transport. The waste products are not reabsorbed and therefore
are excreted in the urine. This complex process of filtration and reabsorption may be difficult to
duplicate in the artificial kidney device.
The artificial kidney device removes excess waste from the blood using the principle of dialysis.
Dialysis represents the movement of solute and water through a semipermeable membrane separating
the two solutions. These artificial kidney devices are also called hemodialyzers. The word “heme”
refers to blood. In the hemodialyzers, blood flows on one side of the semipermeable membrane and
dialysate fluid flows on the other side of the membrane. The membrane in these devices is usually
chosen such that all species, except proteins and blood cells, can potentially transfer. The dialysate
fluid is an aqueous make-up solution consisting of glucose and electrolytes in water, and does not con-
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tain any waste products such as urea, creatinine, uric acid, phenols, sulfates, etc. As the blood flows
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