Acute renal failure Flashcards
Define acute renal failure or ARF or AKI
1) rapid decr in GFR
2) incr plasma creatinine
3) incr urea and waste products (BUN)
Define azotemia
incr BUN and creatinine
3 major etiologies of azotemia
- Pre-renal azotemia
- Post-renal azotemia
- Intrinsic renal disease
Define prerenal azotemia
2 major categories of prerenal cause of ARF
decr in renal plasma flow and/or renal perfusion pressure –> decr GFR
1) hypovolemia (from hemorrhage, GI losses..)
2) low effective arterial blood volume (CHF or cirrhosis)
in prerenal, ___ are undamaged and function normally meaning …
tubules undamaged
continue reabsorb Na+ and H2O to incr volume and perfusion pressure
Pre-renal exam findings include:
1) decr weight andpostural changes in BP/pulse for volume depletion
2) hypervolemic = right heart failure sx = edema, rales, S3
3) UA = high SG (1.020 or 1.030), NO BLOOD, PROTEINS, OR CASTS
4) low FENa
define postrenal azotemia or obstructive nephropathy
decr in GFR due to obstruction of urine outflow from renal papilla to urethra
how does obstruction cause post-renal
1) incr intratubular pressure
2) back up to glomerulus and alter pressure gradients
3) decr GFR due to incr tubular hydrostatic pressure
where can obstruction occur and diseases assoc with each location?
- Ureters
a. Extraureteral – a structure outside the ureter is compressing it; carcinoma of the cervix, retroperitoneal fibrosis
b. Intraureteral – an obstruction within the ureter; kidney stones, blood clots
2. Bladder – outlet obstruction from carcinoma, infection, neuropathy
3. Urethra – prostatic hypertrophy
Post-renal exam findings
1) obstruction = anuria, large changes in urine flow rate
2) UA = specific gravity is isosmotic with NO BLOOD, PROTEINS, CASTS unless have INFECTION
intrinsic renal disease
4 categories and diseases assoc
1) Tubular diseases – acute tubular necrosis (ATN) = most common
2) Glomerular diseases – glomerulonephritis, HUS
3) Interstitial diseases – acute interstitial nephritis (AIN), infection
4) Vascular disease – emboli, renal vein thrombosis
Renal exam findings include
1) Hx of exposure to renal insults assoc with ATN
2) UA for
a) ATN = isotonic, possibly heme, NO PROTEIN, pigmented granular casts and renal tubular epithelial cells
HIGH FENa
b) Glomerulonephritis = heme, protein, RBCs, RBC casts
c) vascultiis = normal to high SG, hematuria, protein, RBCs, RBC casts
if you see RTEs what does patient have
renal –> ATNs
if you see RBC casts what could that indicate?
vasculitis or glomerulonephritis
if you see WBC casts and eosinophils what does that indicate
AIN
Vascular factors that affect ATN and lead to ARF
1) decr in RBF (usual primary event)
2) decr in glomerular permeability
Tubular factors that affect ATN and lead to ARF
1) obstruction of tubule by cellular debris
2) leak of filtrate backwards across membrane
Mechanism of how ATN causes ARF
1) decr RBF
2) ischemia and injury to proximal tubule epithelial cells
3) damaged cells break away from basement membrane
4) expose tubule to back leak
5) decr GFR
6) also obstruct tubule –> incr tubular hydrostatic pressure, further decr GFR
7) ischemia can also damage autoregulation mechanisms in glomeruli
Signs of ATN in patient
1) oliguric (urine volume less than 400 mL)
2) non-oliguric
- manage with fluids/electrolytes
2 complications of ATN
1) infection due to decr leukocyte function
2) GI hemorrahge
certain body insults assoc with developing ATN
1) hypotension
2) surgery with massive hemorrhage
3) transfusion reaction
4) contrast dye
lab findings of ATN
1) pigmented, granular casts
2) renal tubular epithelial cells
3) sometimes blood and protein
4) SG = 1.010
5) FENa > 1% (but may not in non-oliguric ATN or rhabdo or hemolysis or contrast dye)
what are exceptions to incr FENa > 1%
non-oliguric ATN
rhabdo
hemolysis
contrast dye
how do you calculate FENa
FENa = UNa/PNa X PCr/UCr X 100
small #s divided by big #s
if you see low urine Na+ concentration
prerenal because renal tubules still function to reabsorb Na+
what is most common cause of sharp decr GFR
prerenal azotemia
exam findings in prerenal
Urine Na 20
FENa
exam findings in postrenal
Urine Na>20
Urine creatinine 2%
evaluation of postrenal
1) renal US looking for hydronephrosis
2) if obstruct at urethra, bladder cath
3) leftover fluid after cath = post-void residual
Decr in weight
flat neck veins
orthostatic BP and pulse
indicate what?
intravascular volume depletion
= prerenal
edema
pulm rales
S3 gallop
indicate what?
cardiac dysfunction
prerenal AKI
hypervolemia
Hypotension
surgery with blood loss
transfunction reactions
radiocontrast dye
indicate what?
renal insults
–> ATN
anuria
intermittent anuria
indicate what?
urinary obstruction
rash and fever and exposure to antibiotic suggests what
AIN
incr tonicity due to incr ADH suggests what?
prerenal
or SIADH
heme pigmetns without RBCs indicates what
rhabdo
hemolysis
Hyaline casts indicate what
composed of what
benign, normal
tamm-horsfall protein secreted by tubule cells
RBC casts mean what
WBC casts mean what
glomerulonephritis
AIN
locations for cast formation
DCT
collecting duct
high SG
no heme
waxy or finely granular casts
mean what
prerenal azotemia
heme pigment
RBC and RBC casts mean
glomerulonephritis
isotonic urine
WBC
eosinophils
mean
AIN
+/- hematuria
vascular
pigmented coarsely granular casts
renal tubular epith cells mean what
ATN
prerenal urine Na Ucr/Pcr Uosm FENa
1) 20
3) incr
4)
ATN urine Na Ucr/Pcr Uosm FENa
1) >20
2) 2
how to treat prerenal azotemia
1) chf
2) hypovolemia
1) improve CO in CHF
2) replace intravascular volume during hypovolemia
how to treat postrenal
remove obstruction
how to treat ATN
1) remove fluid
2) treat electrolytes
3) dialysis
