48. Acute kidney injury (acute renal failure) Flashcards Preview

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Acute kidney injury is AKA

acute renal failure


acute renal failure - definition

abrupt decline in renal function as measured by increased creatinine and increased BUN


acute renal failure - types

1. prerenal azotemia
2. intrinsic renal failure
3. postrenal azotemia


prerenal azotemia - mechanism

Due to decrease RBF ( eg. hypotension) --> decreased GFR ---> Na+/ H2O and BUN retained by kidney in an attempt to conserve volume --> increased BUN / creatining ratio ( BUN is reasbsobed , creatinine not ) and decreased FENa


Prerenal azotemia - urine osmolarity ( m Osm/kg ), urine Na+ meq/L , FENa, Serum BUN/ Cr

- urine osmolarity ---> more than 500
- urine Na+ less than 20
-FENa less than 1%
-Serum BUN / r >20


Intrinsic renal failure - due to

-acute tubular necrosis or ischemia/ toxins
- less commonly due to acute glomerulonephritis ( RPGN, hemolytic uremic syndrome ) or acute interstitial nephritis


intrinsic renal failure in acute tubular necrosis - mechanism

debris obstructing tubuleand fluid backfolow acrros necrotic tubule --> decreased GFR --> BUN reabsorption is impaired -> low BUN/ creatinine ratio


acute tubular necrosis - casts ?

epithelial / granular casts


intrinsic failure - urine osmolarity ( mOsm/kg ), urine Na+ meq/L , FeNa, serum BUN / cr

- urine osmolarity ---> less than 350
- urine Na+ more than 40
-FENa more than 2%
-Serum BUN / Cr less than 15


post renal azotemia mechanism

Due to outflow obstruction (stones, BPH, neoplasia, congenital anomalies). Develops only with
bilateral obstruction.


Renal failure is the inability

to make urine and exrete nitrogenous wastes


renal failuer - dysplipidemia

- maturation of HDL is impaired and its composition is altered
- clearance of triglyceride - rich lipoproteins and their atherogenic remnants is impaired


consequences of renal failure

Consequences (MAD HUNGER):
ƒƒMetabolic Acidosis
ƒƒDyslipidemia (especially  triglycerides)
ƒƒUremia—clinical syndrome marked by
 BUN:
ƒƒNausea and anorexia
ƒƒ Pericarditis
ƒƒ Asterixis
ƒƒ Encephalopathy
ƒƒ Platelet dysfunction
ƒƒNa+/H2O retention (HF, pulmonary edema,
ƒƒGrowth retardation and developmental delay
ƒƒ Erythropoietin failure (anemia)
ƒƒ Renal osteodystrophy


Chronic renal failure - due to

1. DM ( MC)
2. Hypetenstion
3. Chronic glumerulonephritis ( esp RPGN and Focal Segmental GLomerulosclerosis)
4. Cystic renal disease


• What are three general categories of renal dysfunction that can lead to acute renal injury?

Prerenal (e.g., hypotension and reduced renal blood flow), intrinsic (e.g., tubular necrosis), and postrenal (e.g., outflow obstruction)


• What is acute renal failure?

A condition characterized by an abrupt decline in renal function with elevated blood urea nitrogen and creatinine levels over several days


• A dehydrated man is hypotensive, and his kidneys desperately try to compensate, promoting retention of what three substances?

Sodium, water, and urea (in an attempt to maintain blood volume)


• Why does the blood urea nitrogen (BUN)/creatinine ratio increase in patients who have low renal blood flow (RBF)?

When RBF and the glomerular filtration rate are reduced, urea is absorbed but creatinine is not (known as prerenal azotemia)


• Name the main causes of acute intrinsic renal failure and the characteristic urinary cast that suggests the presence of this condition.

Acute tubular necrosis, ischemia, toxic injury, and, rarely, acute glomerulonephritis;—epithelial/granular (muddy) casts are seen


• A bleeding man has a blood pressure of 95/65 and heart rate of 110. His BUN is 45, creatinine 1.5. Is there prerenal azotemia?

Yes (the BUN:creatinine ratio is >20 [45/1.5 = 30])


• A patient presents with postrenal outflow obstruction that has caused acute renal failure. What are some of the potential causes?

Kidney stones, benign prostatic hyperplasia, congenital anomalies, neoplasia (all must be bilateral unless there is only one kidney)


• The blood urea nitrogen/creatinine ratio is lowest in patients with ____ (prerenal/intrinsic/postrenal) causes of acute renal failure.

Intrinsic (the injured kidneys are unable to absorb urea to maintain blood volume)


• Urine osmolarity >500, urine Na+ <20, FeNa <1%, BUN:creatinine ratio >20 suggests ____ (pre/iintra/post)renal azotemia.



• Urine osmolarity <350, Na+ >40, FeNa >2%, BUN:creatinine ratio >15 suggests ____ (pre/intra/post)renal azotemia.



• Urine osmolarity <350, Na+ >40, FeNa >2%, BUN:creatinine ratio <15 suggests ____ (pre/intra/post)renal azotemia.



• How does the glomerular filtration rate (GFR) change in intrinsic renal failure?

GFR decreases as a result of fluid backflow caused by obstructing necrotic debris in the tubules


• A patient with severe BPH has a FENa of 1.2%. You check a day later, and the FENa has risen to 2.5#37;. What does this tell you?

This suggests progression of his postrenal azotemia (a FENa of >1% suggests mild azotemia, and a FENa of >2% suggests severe azotemia)

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