Acute kidney injury Flashcards
definition: acute kidney injury
reduction in glomerular filtration rate resulting in azotemia developing over a few times
acute kidney injury is commonly due to __________-
renal ischemia or toxins
is AKI reversible or irreversible?
reversible
diagnostic criteria for AKI
- absolute increase in serum creatinine level of 0.3 mg/dL or more
- over 50% increase in serum creatinine
- reduction of urine output less than 500 mL in 24 hr
definition: azotemia
elevation of nitrogenous waste products related to insufficient filtering of blood by the kidneys
definition: oliguria
less than 400-500 mL / day
definition: anuria
less than 50 mL / day
what is the key test to understanding what is going on with the kidney?
UA
creatinine clearance can be used to estimate _____
GFR
serum creatinine levels are inversely proportional to _____
GFR
creatinine clearance _________ (underestimates / overestimates) GFR
overestimates
BUN is a less accurate indicator of GFR than creatinine due to variation in what 3 factors?
- protein intake
- catabolic rate
- tubular reabsorption
what is the cause of urine casts?
trapping of cellular elements in a matrix of protein secreted by renal tubule cells
what type of casts are seen in acute tubular necrosis? what is the appearance of the urine?
- granular casts
- “muddy brown” urine
- age
- NSAIDs
- CKD
these affect which glomerular arteriole? how?
afferent (prevent dilation)
- ACE inhibitors
- ARBs
these affect which glomerular arteriole? how?
efferent (prevent angiotensin II mediated vasoconstriction)
what are the three types of AKI?
- pre-renal
- renal
- post-renal
what is the etiology of pre-renal AKI? what is one major condition associated with it?
- impaired effective renal perfusion
- volume depletion
what is the etiology of renal AKI? what is one major condition associated with it?
- intrinsic renal disease (glomerular, tubular, interstitial, vascular)
- acute tubular necrosis
what is the etiology of post-renal AKI? what is one major condition associated with it?
- obstruction of urinary flow
- BPH, tumor
prerenal AKI has decreased GFR ________ (with / without) ischemic or nephrotoxic injury to tubules
without
what is the BUN : creatinine ratio for prerenal AKI?
over 20 : 1
what type of casts can be seen in prerenal (volume depleted) AKI?
hyaline
what is the most common cause of renal AKI?
acute tubular necrosis (ATN)
what are the morphologic features of ATN?
- tubular dilation
- attenuation of tubular epithelium
- loss of epithelial cell brush border
- granular cast material
- mitotic figures
can tubule cells regenerate following ATN?
yes
what is obstructive uropathy?
obstruction of the urinary tract at any level that affects both kidneys
what should be ruled out in all patients with oliguria?
obstructive uropathy (post-renal AKI)
what is hydronephrosis?
distension and dilation of the renal pelvis calyces
what test is used to differentiate prerenal AKI from ATN?
assessment of urine sodium excretion
what test do you use to exclude postrenal AKI?
renal imaging (US, CT)
how is fractional excretion of sodium expressed?
amount of sodium excreted over amount of sodium filtered by glomeruli
in the setting of volume depletion, urine Na reabsorption should be _________ (increased / decreased) in the proximal tubules
what would the FENa be?
- increased
- FENa less than 1%
if the proximal tubules are injured via ATN, how is sodium handling affected? what is the FENa result?
- reabsorption will be impaired?
- FENa over 2%
what lab helps to differentiate between prerenal azotemia and ATN?
FENa
what is the FENa level in ATN? prerenal azotemia?
- ATN: over 2%
- prerenal azotemia: less than 1%
