SM 195a - AKI: Pre, Post, and Intrinsic

Question 1

What diagnostic studies could help you diagnose post-renal AKI?

Answer 1

• Post-void residual bladder volume reveals lower tract obstruction
• Renal ultrasound reveals upper tract obstruction
• Non-contrast CT
• BUN/Serum Cr ratio
  
  • >20:1 implies enhanced urea reabsorption
  • Also elevated in prerenal AKI

Question 2

The presence of eosinophils, WBCs, and WBC casts in the urine would increase your suspicion for which cause of AKI?

What would you expect from urine Na+?

Answer 2

Acute Interstitial Nephritis (AIN)

Urine Na+ >30 mEq/L
(This implies that the tubules are not working to reabsorb Na+)

Question 3

What laboratory results would be consistent with pre-renal AKI?

• Urin Na:
• FENa:
• BUN/SCr:
• Sediment:

Answer 3

• Urin Na: < 20 mmol/L
  
  • ​Implies increased Na+ reabsorption
• FENa: <1%
• BUN/SCr: >20
  
  • ​Implies increased reabsorption of urea
• Sediment: bland
  
  • Implies no intrinsic kidney injury

These numbers are consistent with physiological responses to decreased perfusion to the kidney

Question 4

What lab results would be consistent with interstitial AKI?

Answer 4

• Blood, WBCs in the urine
• Eosinophils in the urine
• WBC casts

Use of nephrotoxic drugs and/or recent infection increase suspicion for acute interstitial nephritis (AIN) as a cause of AKI

Question 5

Describe the pathophysioogy of hepatorenal syndrome

Answer 5

Healthy kidneys, diseased liver

• Splanchnic artirial vasodilation
• -> Compensatory vasconstriction in other systems
• -> Impaired Na+ and H2O handling
• -> Ascites, edema
• -> Further decrease in effective blood volume

PE findings are consistent with prerenal AKI that is unresponsive to volume repletion

Question 6

What causes of intra-tubular obstruction can cause ATN?

Answer 6

• Myeloma
  
  • -> Proteins aggregate and block tubules
• Tumor lysis syndrome
  
  • -> Uric acid crystalization
• Drugs: Acyclovir, methotrexate

Question 7

What is hepatorenal syndrome?

Answer 7

Basically, pre-renal AKI caused by liver failure

• A consequence of renal vasoconstriction in the setting of normal kidneys and andvanced liver disese
• Pre-renal AKI unresponsive to volume repletion
• Oliguria, bland urine sediment, UNa <10

Question 8

Aldosterone and ADH are secreted in response to
________ glomerular filtration.

What is the effect?

Answer 8

Aldosterone and ADH are secreted in response to
decreased glomerular filtration.

Aldosterone -> increased Na+ reabsorption

ADH -> increased H2O reabsorption

The result is concentrated urine with low Na+ content

(conservation of sodium and water to increase blood volume)

Question 9

How is AKI diagnosed?

Answer 9

ONE of the following

• Increase in serum creatinine
  
  • Increase of 0.3 mg/dL above baseline in 48h
  • Increase in serum creatinine of 1.5x baseline in 7 days
• Decrease in urine output
  
  • <0.5 mL/kg/hr for 6 hours