103114 acute kidney injury Flashcards
acute kidney injury is also called
acute renal failure
acute kidney injury
reduction in GFR resulting in azotemia developing over days
usually reversible
absence of symptoms of chronic uremia
kidney size usually preserved
what are the common causes of acute kidney injury
renal ischemia or toxins
diagnositic criteria for AKI
abrupt (48 hr) reduction in kidney fxn defined as
an absolute increase in serum creatinine level of 0.3 mg/dl or
percentage increase in serum creatinine of greater than 50% or
reduction in urine output to
oliguria
urine output under 400-500 mL/day
azotemia
elevation of nitrogen waste products related to insufficient filtering of blood by kidneys
uremia
illness accompanying kidney failure which results from toxic effects of abnormally high concnetrations of nitrogenous substances in blood
what tests can be used in AKI?
serum creatinine
blood urea nitrogen
urinalysis
urinalysis testing for AKI can look for what?
casts-caused by trapping of cellular elements in a matrix of protein secreted by renal tubule cells
granular casts (muddy brown urine) are seen in acute tubular necrosis
how does autoregulation of GFR occur under decreased perfusion pres?
increased vasodilatory prostaglandins at afferent arteriole
increase angiotensin II at efferent arteriole
some cases of kidney injury can be precipitated when there’s a loss of these autoregulatory mechanisms
how can autoregulation of GFR be altered?
elderly, NSAIDs, CKD–do not have normal vasodilatory prostaglandin response
ppl taking ACEi and ARBs cannot mount the normal angiotensin II constriction response
so for these ppl, even at modest decrease in MAP, they will have a decrease in GFR
what are possible causes of pre-renal AKI?
volume depletion
heart failure
liver failure
possible causes of renal AKI
acute tubular necrosis
interstitial nephritis
glomerulonephritis
vascular diseases
possible causes of post-renal AKI
obstruction-prostate, bladder, stones, tumors
prerenal AKI definition
due to decreased effective renal perfusion
decreased GFR WITHOUT ischmemic or nephrotoxic injury to tubules
pathogenesis of prerenal AKI
decreased effective renal perfusion, leading to increased ang II and vasopressin, leading to increased reabosprtion of Na at proximal tubule and water, leading to CONCENTRATED URINE AND OLIGURIA
increased reabsorption of urea, leading to elevation of BUN out of proportion to creatinine (>20:1)
renal AKI
acute injury involving tubules, glomeruli, interstitium or vasculature
ex:
acute tubular necrosis: ischemic, toxic, both
inflam: glomerulonephritis, tubulointerstitial neprhitis, vasculitis
embolism, thrombosis, thrombitc microangiopathy
neoplasms: infiltrating tumors
most common cause of “renal” AKI
acute tubular necrosis
mechanisms of acute tubular necrosis
if ischemic-can cause endothelial cell dysfxn and vasoconstriction. can cause tubule cell injury and reversible or irreversible damage. ultimately all of the above lead to reduced GFR and oliguria
morphologic features of ATN
tubular dilatation attenuation of tubular epithelium loss of epithelial cell brush border granular cast material mitotic figures (regenerative change)
how does tubule regeneration occur in ATN?
sublethally injured tubular epithelial cells dedifferentiate, proliferate, migrate, and reestablish cell polarity
morphology of post renal AKI
hydronephrosis-distension and dilation of renal pelvis calyces
how can you distinguish prerenal AKI from acute tubular necrosis (both have oliguria)
changes in urine sodium reabsoprtion–look at urine sodium excretion
in volume depletion–urine Na reabsoprtion should be increased in proximal tubules—FENa2%
eqn for FENa
UNa * PCr / (PNa * UCr) multiplied by 100
symptoms of ECF volume depletion
hypotension
oliguria
in chronically hypertensive individuals, what happens to GFR autoregulatory curve?
shifted to the right. so when lower their BP, their BP falls out of the regulatory range even when it’s a normal BP
also, if they are on lisinopril (ACEi), they don’t have maintained efferent arteriolar tone, so can’t keep up good GFR
is acetaminophen nephrotoxic?
no
what is septic shock an ex of in terms of AKI?
acute tubular necrosis
