OnlineMedEd: Intern Content - "Renal Failure"

Question 1

Review the causes of prerenal AKI.

Answer 1

• Cardiogenic: MI or CHF leads to heart not pumping enough blood
• Intravascular volume depletion: dehydration, diarrhea, vomiting, hemorrhage
• Interstitial losses (“3rd spacing”): cirrhosis, nephrosis, gastrosis
• Blockage: atherosclerotic occlusion of the renal vessels, thrombosis, or fibromuscular dysplasia

Question 2

Review the causes of postrenal AKI.

Answer 2

• Kidney, ureter, and bladder: cancer, stones, ureteropelvic junction abnormalities (congenital)
• Prostate: BPH, cancer

Question 3

How can a urinalysis tell you what the cause of intrinsic renal failure is?

Answer 3

• Glomerulonephritis: RBC casts
• ATN: muddy casts
• AIN: eosinophils, WBC casts, WBCs

Question 4

Describe the three phases of acute tubular necrosis.

Answer 4

• Initial phase: anuric, this is when the insult happens
• Maintenance phase: oliguric, metabolic derangements secondary to decreased GFR (e.g., hyperkalemia)
• Recovery phase: polyuric, low levels of all electrolytes (hyponatremia, hypokalemia, hypomagnesemia, and hypocalcemia)

Remember the Sketchy scene:

• on left, the kid has a malfunctioning water gun (anuric);
• in the middle, the Grounds FIlter is broken and the coffee machine is barely working;
• on the right, the trashcan has spilled over and knocked the sodium, calcium, bananas, and magnesium on the floor and they’re getting sprayed by the water

Question 5

List the two ratios that suggest prerenal disease.

Answer 5

• BUN:Cr > 20

* FeNa < 1%

Question 6

What is “the big mistake” that people make when managing prerenal AKI?

Answer 6

They jump to give fluids. This is wrong because if a person has prerenal AKI secondary to CHF, then diuresis is the correct treatment.

Question 7

Lots of sodium flow through the nephron does what to renin?

Answer 7

It turns it off.

Question 8

FeNa can be confounded by ________________.

Answer 8

any use of diuretic (loop, DCT, or collecting duct agents)

Also, it is only useful in those with oliguria.

Question 9

Because the FeNa and BUN:Cr ratios are subject to confounding, the best way to handle suspected prerenal azotemia is _______________.

Answer 9

to give fluids and recheck a BMP (in a dehydrated person) or to give diuresis and recheck a BMP (in a volume-overloaded person)

Question 10

How should you diagnose intrinsic renal failure?

Answer 10

Officially, a biopsy is needed. However, history and physical can usually get you there:

• Does the person have diabetes? Probably diabetic nephropathy.
• Does the person have lupus? Probably lupus nephritis.
• Does the person have HBV or HCV? Probably MPGN.