What is acute renal failure?
Severe, acute decrease in renal function (develops within days)
What is the hallmark of ARF?
Azotemia
What is azotemia?
Increased BUN and creatinine, often with oliguria
What causes prerenal azotemia?
Decreased blood flow to the kidneys; common cause of ARF
What are the results of the decreased blood flow in prerenal azotemia?
Decreased GFR
Azotemia
Oliguria
How are serum BUN:Cr ratio, fractional excretion of sodium, and urine osmolality affected in prerenal azotemia?
Serum BUN:Cr ratio > 15
[FENa] < 1%
Urine osm > 500mOsm/kg
What causes postrenal azotemia?
Obstruction of urinary tract dwonstream from the kidney
What are the results of the decreased outflow in postrenal azotemia?
Decreased GFR
Azotemia
Oliguria
How are serum BUN:Cr ratio, fracional excretion of sodium and urine osmolality affected in postrenal azotemia?
EARLY:
serum BUN:Cr ratio > 15
FENa < 1%
Urine osm > 500 mOsm/kg
LATE:
serum BUN:Cr ratio < 15
FENa > 2%
Urine osm < 500mOsm/kg
What causes intrarenal azotemia?
Injury and necrosis of tubular epithelial cells
MCC of ARF
How does a decrease in GFR arise in acute tubular necrosis (intrarenal azotemia)?
Necrotic cells plug the tubules, obstructing the filtration flow
What kind of casts are seen in acute tubular necrosis?
Brown granular casts are seen in the urine
Arise from the necrotic cells that plug the tubulues
How are serum BUN:Cr ratio, fracional excretion of sodium and urine osmolality affected in acute tubular necrosis?
serum BUN:Cr ratio < 15
FENa > 2%
urine osm < 500 mOsm/kg
What are the two possible etiologies of acute tubular necrosis?
Ischemia
Nephrotoxic
What often precedes ischemic acute tubular necrosis?
prerenal azotemia
What parts of the kidneys are especially susceptible to ischemic damage?
Proximal tubule and medullary segment of the thick ascending limb
What part of the kidney is most susceptible to nephrotoxic damage?
Proximal tubule
What are the clinical features of acute tubular necrosis?
Oliguria with brown granular casts
Elevated BUN and creatinine
Hyperkalemia (due to decreased renal excretion) with metabolic acidosis
What is acute interstitial nephritis?
Drug-induced hypersensitivity involving teh interstitium and tubulues; results in acute renal failure (intrarenal azotemia)
What are common causes of acute interstitial nephritis?
NSAIDs
Penicillin
Diuretics
Clinical presentations of acute interstitial nephritis?
Oliguria, Fever, Rash days to weeks after starting a drug
Eosinophils may be seen in the urine
What can acute interstitial nephritis progress to?
Renal papillary necrosis
What does renal papillary necrosis present with?
Gross hematuria
Flank pain
Causes of renal papillary necrosis
chronic analgesic abuse
DM
sickle cell trait or disease
severe acute pyelonephritis
