Chapter 25
Renal Failure
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When Kidneys Fail
• Less waste is removed
• More waste remains in the blood
• Nitrogenous compounds build up in the blood
– BUN: Blood urea nitrogen
– Creatinine
• Renal function approximated by:
initial creatinine level/current creatinine level
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Acute Renal Failure
• Prerenal
– Decreased blood supply
• Shock, dehydration, vasoconstriction
• Postrenal
– Urine flow is blocked
• Stones, tumors, enlarged prostate
• Intrinsic
– Kidney tubule function is decreased
• Ischemia, toxins, intratubular obstruction
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Question
Which type of acute renal failure (ARF) would be most
likely to accompany benign prostatic hypertrophy?
a. Prerenal
b. Postrenal
c. Intrinsic
d. Extrinsic
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Answer
b. Postrenal
Postrenal ARF occurs when the flow of urine is blocked by
kidney stones, tumors, or an enlarged prostate gland.
Because the male urethra passes through the prostate, if
it is enlarged, the urethra may become blocked.
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Radiocontrast Agents Can Cause ARF
• Giving N-acetylcysteine reduces the risk of
ARF by 50% in a meta-analysis
• Recommended for clients at risk of renal
failure who are receiving radiographic
contrast media
– Diabetics, clients with sepsis
– Underlying vascular, renal, or hepatic
disease
– Receiving other nephrotoxic drugs
(Kellum, J.A. [2003]. A drug to prevent renal failure? Lancet 362,589-590.)
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Scenario
A man developed acute renal failure after emergency
surgery for a severed left leg
• He came in with a serum creatinine of 1.2 mg/dL, but
now it is 5.6 mg/dL
• His BUN is 86 mg/dL
Question:
• Why would leg damage cause renal failure?
• What is his remaining kidney function?
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Urine Containing Tubular Cell Casts
• Casts are formed
when cells are packed
together in the tubule
lumen
• They block the tubule
• When the mass of
cells washes loose, it
appears in the urine
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Scenario
Mr. J is an alcoholic with kidney problems
• He is severely dehydrated with an infected leg
ulcer, benign prostatic hypertrophy, and anemia
• His urine is dark and contains myoglobin and
tubular cell casts
• His creatinine and BUN are both elevated
Question:
• What may have caused his acute tubular
necrosis?
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Chronic Renal Failure
• Fewer nephrons are functioning
• Remaining nephrons must filter more
– Hyperperfusion
– Hypertrophy
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Development of CRF
• Diminished renal reserve
– Nephrons are working as hard as they can
• Renal insufficiency
– Nephrons can no longer regulate urine density
• Renal failure
– Nephrons can no longer keep blood
composition normal
• End-stage renal disease
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Uremia
• Uremia = “Urine in the Blood”
• Renal filtering function decreases
– Altered fluid and electrolyte balance
o Acidosis, hyperkalemia, salt wasting, hypertension
• Wastes build up in blood
– Increased creatinine and BUN
o Toxic to CNS, RBCs, platelets
• Kidney metabolic functions decrease
– Decreased erythropoietin
– Decreased Vitamin D activation
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Question
Which of the following renal disorders is characterized by
increased BUN and creatinine levels?
a. ARF
b. CRF
c. Uremia
d. All of the above
e. b and c
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Answer
d. All of the above
In each disorder listed, the ability to remove nitrogenous
waste is diminished. This causes nitrogenous
compounds (BUN and creatinine) to accumulate in the
blood.
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Scenario
A man has chronic renal failure.
• He has high creatinine and BUN, hyperkalemia, acidosis
with normal pCO2, and severe anemia
• His blood glucose has reached 340 mg/dL one hour after a
hospital meal
• He complains of having broken two toes in the last few
weeks, even though he eats a lot of dairy products for
calcium
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Scenario (cont.)
Question:
• What is the most likely cause of his chronic renal
failure?
• What caused his anemia?
• Why are his bones brittle even though he eats
dairy products?
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Cardiovascular
Consequences of CRF
less
erythropoietin
• Decreased blood
viscosity
anemia
+
lower blood
viscosity
• Increased blood
pressure
+
• Decreased oxygen
supply
blood flows through
vessels more swiftly
heart rate increases
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increased workload on left heart
left ventricle dilation and
hypertrophy
not enough oxygen to support LV
contraction
angina
ischemia
LHF
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Question
Tell whether the following statement is true or false.
CRF leads to decreased cardiac output (CO).
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Answer
True
The increased blood pressure (HTN) and hypoxemia that
accompany CRF lead to increased myocardial work (the
heart has to work harder to meet the metabolic demands
of body tissues). Eventually the heart becomes unable to
meet these metabolic demands, and CO will decrease.
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