Chapter 42
Acute Renal Injury and Chronic Kidney Disease
1117
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.
Chronic kidney disease
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
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
