Porth's Pathophysiology, 9e

Chapter 42 Acute Renal Injury and Chronic Kidney Disease    1117

Definition and Classification In 2002, the Kidney Disease Outcome Quality Initiative (K/DOQI) of the National Kidney Foundation (NKF) published clinical practice guidelines for CKD. 14 The goals of the Work Group that developed the guidelines were to define CKD and classify its stages, to evaluate laboratory mea- sures used for assessment of kidney disease, and to asso- ciate the level of kidney function with the complications of CKD. The guidelines use the GFR to classify CKD into five stages, beginning with kidney damage with normal or elevated GFR, progressing to CKD and, potentially, to kid- ney failure. It is anticipated that early detection of kidney damage along with implementation of aggressive measures to decrease its progression can delay or prevent the onset of kidney failure. 2 According to the NKF guidelines, individuals with a GFR of 60 to 89 mL/min/1.73 m 2 (corrected for body surface area) without kidney damage are classified as “decreased GFR.” 14 Decreased GFR without recognized markers of kidney damage can occur in infants and older adults and is ­usually considered to be “normal for age.” Other causes of chronically decreased GFR without kidney damage in adults include removal of one kidney, extracellular fluid volume depletion, and systemic illnesses associated with reduced kidney perfusion, such as heart failure and cirrhosis. 14 Even at this stage, there is often a characteristic loss of renal reserve. CKD is defined as either kidney damage or a GFR less than 60 mL/min/1.73 m 2 for 3 months or longer. 14 CKD can result from a number of conditions that cause permanent loss of nephrons, including diabetes, hypertension, glomerulone- phritis, systemic lupus erythematosus, and polycystic kidney disease. Remember Mr. Reterez who was introduced to you in Chapter 38? He had been diagnosed with polycystic kidney disease. With this genetic disor- der, a person manifests symptoms in his or her fourth decade. Mr. Reterez is 45 years of age. His GFR is most likely less than 60 mL/minute, which indicates that he is retaining nitrogenous waste. In addition, his BUN is rising as well as his creatinine (BUN = 45, creatinine = 2.0 at Emergency Department visit). His symptoms are all due to CKD. Hypertension and diabetic kidney disease are the two main causes of CKD in the United States. 2 The NKF Practice Guidelines define kidney failure “as either 1. A GFR of less than 15 mL/min/1.73 m 2 , usually accompanied by most of the signs and symptoms of uremia, or 2. A need to start renal replacement therapy (dialysis or transplantation)” 14

of ­nitrogenous wastes in the blood ( i.e., azotemia), and ­alterations in body fluids and electrolytes. Acute renal failure is classified as prerenal, intrinsic or intrarenal, or postrenal in origin. Prerenal failure is caused by decreased blood flow to the kidneys, postrenal failure by obstruc- tion to urine output, and intrarenal failure by disorders in the kidney itself. ATN or AKI, due to ischemia, sepsis, or nephrotoxic agents, is a common cause of acute intrarenal failure. ATN typically progresses through three phases: the initiation phase, during which tubular injury is induced; the maintenance phase, during which the GFR falls, nitroge- nous wastes accumulate, and urine output decreases; and the recovery or reparative phase, during which the GFR, urine output, and blood levels of nitrogenous wastes return to normal. Because of the high morbidity and mortality rates associ- ated with acute renal failure, identification of people at risk is important to clinical decision making. New biomarkers such as IL-18, NGAL, and kidney injury molecule-1 are in ­various trial stages, which should be helpful in earlier ­assessment of AKI in the future. Acute renal failure often is reversible, making early identification and correction of the underlying cause ( e.g., improving renal perfusion, discontinuing nephrotoxic drugs) important. Treatment includes the judicious administration of fluids and hemo- dialysis or CRRT. After completing this section of the chapter, you should be able to meet the following objectives: •• State the most common causes of chronic kidney disease. •• Explain the physiologic mechanisms underlying the common problems associated with chronic kidney disease, including alterations in fluid and electrolyte balance and disorders of skeletal, hematologic, car- diovascular, immune system, neurologic, skin, and sexual function. •• State the basis for adverse drug reactions in people with chronic kidney disease. •• Citethepossiblecomplicationsofkidneytransplantation. CKD is a worldwide problem that affects people of all ages, races, and economic groups. The prevalence and incidence of the disease, which mirror those of conditions such as diabe- tes, hypertension, and obesity, are rising. In the United States alone, more than 20 million people, or 1 in 9 adults have CKD. Another 20 million people are at increased risk for develop- ment of the disorder. 1 Chronic kidney disease