chapter 25 renal failure

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Chapter 25

Renal Failure


When Kidneys FailWhen 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


Acute Renal FailureAcute 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


Question 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


Answer 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.


Radiocontrast Agents Can Cause ARFRadiocontrast 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.)


ScenarioScenario

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?


Urine Containing Tubular Cell CastsUrine 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


ScenarioScenario

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?


Chronic Renal FailureChronic Renal Failure

• Fewer nephrons are functioning

• Remaining nephrons must filter more

– Hyperperfusion

– Hypertrophy


Development of CRFDevelopment 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


UremiaUremia

• 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


Question 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


Answer 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.


ScenarioScenario

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


Scenario (cont.)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?


Cardiovascular Consequences of CRFCardiovascular Consequences of CRF

• Decreased blood viscosity

+

• Increased blood pressure

+

• Decreased oxygen supply

less erythropoietin

anemia

lower blood viscosity

blood flows through vessels more swiftly

heart rate increases


left ventricle dilation and hypertrophy

not enough oxygen to support LV contraction

anginaischemia

LHF

increased workload on left heart


Question Question

Tell whether the following statement is true or false.

CRF leads to decreased cardiac output (CO).


Answer 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.

chapter 25 renal failure

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