Pathoma12.2 Acute Renal Failure (ARF) Flashcards
What are the 2 hallmarks of acute renal failure (ARF)?
Azotemia
oliguria
What is azotemia
increased BUN and Creatinine (Cr)
What causes prerenal azotemia
decreased BF to kidneys
what is a normal BUN:Cr ratio?
15
when the tubule is intact, what is the fractional excretion of Sodium [FENa] and urine osmolality [osm]
FENa <1%
[osm] > 500mOsm/kg
What happens to BUN:Cr ratio in prerenal azotemia?
it increases >15
What is Mechnism of BUN:Cr increase in prerenal azotemia?
decreased GFR –> decreased Na–> renin–> Aldo–> Na and water reabsorbed–> BUN reabsorbed–> increased BUN:Cr ratio
what happens to FENa and urine osm in prerenal azotemia and why
nothing
what happens to FENa and urine osm in early stages of postrenal azotemia and why
nothing= normal
what happens to FENa and urine osm in late stage postrenal azotemia and why
FENa increases (>2%) because tubule can’t reabsorb sodium and [osm] decreases (<500) bc can’t concentrate urine
what is cause of Postrenal azotemia (MOA)
obstruction of urinary tract (ureter) downstream from kidney–> decreased outflow–> decreased GFR (backpressure), azotemia, oliguria
BUN:Cr in early postrenal azotemia and why?
> 15 because increased tubular pressure forces BUN into blood
BUN:Cr in late postrenal azotemia and why?
<15 because tubular damage makes reabsorbing BUN impossible–> decreased BUN:Cr
What are the 2 forms of intrarenal azotemia?
Acute tubular necrosis
Acute interstitial nephritis
What happens to GFR in Acute tubular necrosis and why
decreases becuase necrotic tubular cells plug the tubule
What is seen in the urine in Acute tubular necrosis
brown, granular casts (made of necrotic tubular cells)
What happens to BUN:Cr in Acute tubular necrosis
decreased
What does BUN reabsorption depend on ***
normal/intact tubular cells
What happens to FENa and urine osm in Acute tubular necrosis
FENa increases (>2%) because can't reabsorb sodium [osm] decreases (<500) because can't concentrate urine
2 etiologies of Acute Tubular necrosis
Ischemia
Nephrotoxic
Ischemic Acute Tubular necrosis affects what parts of the tubule?
PCT, medullary segment of TAL
Nepphrotoxic Acute Tubular necrosis affects what parts of the tubule?
PCT
6 common causes of Nephrotoxic Acute Tubular necrosis
- Aminoglycosides
- Urate (tumor lysis syndrome)
- Lead
- Myoglobinuria (crush injury)
- ethylene glycol (oxalate crystals in urine)
- radiocontrast dye
What is tumor lysis syndrom eand why does it cause nephrotoxic Acute Tubular necrosis?
chemothx kills large amounts of cells which leads to release of nuclear contents including uric acid–>tubular damage
