Acute Kidney Injury Flashcards
In acute kidney injury, there is a reduction in _____ resulting in ______ developing over days
GFR; azotemia
What are common causes of acute kidney injury?
Renal ischemia or toxins
How is kidney size affected in AKI?
Kidney size is usually preserved
What are some of the diagnostic criteria for AKI?
- An abrupt (within 48 hours) reduction in kidney function defined as
- An absolute increase in serum creatinine level of 0.3 mg/dl or
- A percentage increase in serum creatinine level of ≥ 50% or
- A reduction in urine output < 500 mL in 24 hours
Define the following:
- Oliguria:
- Azotemia:
- Uremia:
- Oliguria: Urin output < 400-500 ml/day
- Azotemia: Elevation of nitrogen waste products related to insufficient filtering of blood by the kidneys
- Uremia: The illness accompanying kidney failure which results from the toxic effects of abnormally high concentrations of nitrogenous substances in the blood
Serum creatinine levels are inversely proportionate to ___
GFR
What are the limitations of creatinine compared to inulin?
Unlike inulin, creatinine is also secreted in the nephron and creatinine clearance overestimates GFR
What is BUN and when is it used to diagnose renal disease?
Blood Urea Nitrogen - nitrogenous waste product of protein metabolism
Useful in conjunction with creatinine in the differential diagnosis of renal disease - less accurate than creatinine due to variation in protein intake, catabolic rate, and tubular reabsorption
How are casts formed and how do they present in acute tubular necrosis?
Casts are caused by the trapping of cellular elements in a matrix of protein secreted by renal tubules
Granular casts - muddy brown urine - are seen in cases of acute tubular necrosis
Autoregulation of GFR and RBF is effective between the blood pressures of __ and __
80 and 160
What GFR autoregulation mechanisms can compensate for decreased perfusion pressure?
Increased vasodilatory prostaglandins - dilate afferent arterioles
Increased angiotensin II - Constrict efferent arteriole
With impaired autoregulation _____ _____ has greater effect on GFR
arterial pressure
What are the three categories of AKI?
- Pre-renal: imparied effective renal perfusion
- Renal: intrinsic renal disease
- Post renal: obstruction of urinary flow
Pre-renal AKI consists of decreased GFR without _____ or _____ injury to tubules
ischemic or nephrotoxic
How does pre-renal AKI lead to oliguria?
Decreased effective renal perfusion → increased Ang II and vasopressin → increased reabsorption of sodium (at proximal tubule) and water → concentrated urine → oliguria
Pre-renal AKI is associated with increased reabsorption of urea
Elevation of ____is out of proportion to creatinine?
elevation of BUN is out of proportion to creatinine (>20:1)
How does the tubular epithelium appear in pre-renal AKI?
normal
What is the most common cause of renal AKI?
Acute tubular necrosis
What are some causes of Renal AKI?
- ATN
- Inflammation: glomerulonephritis, tubulointerstitial nephritis, vasculitis
- Embolism, thrombosis, thrombotic miroangiopathy
- Neoplasms: infiltrating tumors
What are some morphologic features of acute tubular necrosis (ATN)?
- Tubular dilation
- Attenuation of tubular epithelium
- Loss of epithelial cell brush border
- Granular cast material
- Mitotic figures (regenerative change)
How do tubules regenerate after ATN?
Sublethally injured tubular epithelial cells repopulate the tubules by:
De-differentiation → proliferation → migration → re-establishing cell polarity
What are some causes of Post-renal AKI?
Bladder outlet obstruction
Ureteral obstruction
How many kidneys are affected in Post-Renal AKI?
both
What is hydronephrosis (in post renal AKI)?
Distension and dilation of the renal pelvis calyces
How can fractional excretion of sodium (FENa) distinguish pre-renal AKI from acute tubular necrosis?
- In the setting of volume depletion urine Na reabsorption should be increased in the proximal tubules → FENa < 1%
- If the proximal tubules are injured (ATN), sodium reabsorption will be impaired → FENa > 2%
How do you calculate FENa?
FENa = [(UNa x PCr)/ (PNa x Ucr)] x 100
