AKI Flashcards
define acute kidney injury
- abrupt loss of kidney function resulting in
- retention of urea and other nitrogenous waste products
- dysregulation of volume status and electrolytes
GFR
estimates how much blood passed through the glomeruli each minute to be filtered
what are the criteria for diagnosis of acute kidney injury
- serum creatinine levels
- decrease in urine output
can you still use serum creatinine to assess kidney function in patient undergoing dialysis
no, creatinine is removed by dialysis
Define the RIFLE acronym
- Risk
- Injury
- Failure
- Loss
- ESRD
- *first three are levels of severity; last two are outcome measures
what three groups have come up with ways to define AKI
- RIFLE
- AKIN
- KDIGO
what is RIFLEs definition of AKI using serum creatinine
- increase in serum creatitine > 50% developing over 7 days
what is AKIN’s definition of AKI using serum creatinine
- increase in serum creatinine of 0.3 mg/dL pr > 50% developing over 48 hours
AKI can be classified into what 3 categories
- Prerenal: decreased renal perfusion
- Intrinsic renal: pathology of vessels, glomeruli, or tubules-interstitium
- Postrenal: obstructive
What are some causes of Prerenal AKI
- True volume depeletion
- V/D; burns, third spacing from crush injury
- Hypotension
- shock or aggressive tx of HTN
- Edematous status
- heart failure, cirrhosis
- Bilateral renal artery stenosis
- Drugs affecting GFR
- NSAIDs
What are some causes of Intrinsic renal AKI
-
renal ischemia
- from all causes of severe prerenal dz
- sepsis
-
nephrotoxins
- aminoglycosides, IV contrast, rhabdomyolysis
How does IV contrast affect kidneys
- causes renal tubular epithelial cell toxicity and renal medullary ischemia
risk factors for kidney damage by IV contrast
- pre-existing renal disease
- volume depletion
- repeated doses of contrast
prevention of kidney damage by IV contrast
- hydration
- avoidance of nephrotoxic drugs for at least 48 hours after exposure
- e.g metformin
define Nonoliguric
>400 mL/24 hours
Define Oliguric
<400mL/24 hr
define Anuric
<100mL/24 hr
important labs to get when evaluating AKI
- UA
- creatinine
- calculation of GFR
- calculatoin of fractional excretion of sodium (FENa)
first line imaging to get when evaluating AKI? what are you evaluating for
- renal US
- assess for urinary tract obstruction
most dipsticks permit the analysis of the following core urine parameters
- Heme
- Leukocyte esterase
- Nitrite
- Albumin
- Hydrogen ions (pH)
- specific gravity
- Glucose
muddy brown casts are pathognomonic for
Acute tubular necrosis
What are the two most commonly used equations for calculating GFR
- Crockcroft-Gault
- Modification of Diet in renal disease (MDRD)
how is the fractional excretion of sodium (FENa) used
- measures urine sodium
- in an oliguric patient, the FENa may help to distinguish prerenal AKI from intrinsic renal pathology
what is the equation for fractional excretion of sodium (FENa)? What values suggest prerenal and ATN?
FENa = (urine Na / Serum Na) / (Urine Cr / Serum Cr) x 100
- < 1% suggests prerenal etiology
- >2% suggests intrarenal (ATN)
when can you not rely on the fractional excretion of sodium (FENa) equation
- cannot be used in patients on diuretics
- can’t be used with chronic renal failure
- only useful in acute renal failure
When is a renal biopsy indicated
- for patients who have no clear explanation for AKI
- if the creatinine is markedly elevated or if it significantly worsens over the course of days
- biopsy will provide more definitive tissue diagnosis
contraindications to getting a renal biopsy
- solitary native kidney
- bleeding diathesis
- hydronephrosis
- pyelonephritis
- renal tumor
List the life-threatening complications that can come from AKI
- volume imbalance: depletion or overload
- metabolic acidosis
- hyperkalemia
- hypocalcemia
- hyperphosphatemia
- uremia
- **generally require hemodialysis
if patient has a h/o consistent with fluid loss (V/D), a physical exam consistent with hypovolemia (hypotension, tachycardia) and/or oliguria, treatment is
- IV fluids
- fluid challenge attempts to identify prerenal failure
- crystalloid isotonic fluid (0.9 nml saline) is preferred
how much fluid is given
- begin with 1-3 liters of fluid with careful and repeated clinical assessment
- pts who do not respond to fluids are unlikely to have prerenal disease
if patient becomes volume overloaded or develops fluid retention from IV fluid therapy then treatment is
- diuretics (typically furosemide) = temporizing measure
- should not be prolonged therapy
- dialysis offers most efficient method of volume removal
how does AKI lead to metabolic acidosis
- excretion of acid and regeneration of bicarbonate is impaired with a low GFR
- causes of AKI such as sepsis, trauma, and multi-organ failure produces increased amount of acid
how does diarrhea worsens metabolic acidosis
causes net loss of bicarbonate
treatment options for metabolic acidosis from AKI
- dialysis
- bicarbonate administration
- choice depends on presence of volume overload and the underlying cause of acidosis
when should a patient with metabolic acidosis from AKI be dialyzed
- patients with severe oligo-anuric AKI who are volume overloaded and have severe metabolic acidosis ( pH <7.1)
- bicarb adminstration results in large sodium load that may cause or increase volume overload
when should a patient with metabolic acidosis from AKI be given bicarbonate
- patients with AKI who are not volume overloaded and
- acidosis is related to diarrhea
- pH < 7.1 and awaiting dialysis
- AKI due to rhabdomyolysis
- goal: serum bicarb 20-22 mEq/L and pH > 7.2
hyperkalemia can cause
- impaired neuromuscular transmission
- cardiac conduction abnormalities (arrhythmias)
how does AKI cause hypocalcemia and hyperphosphatemia
- increases in serum phosphorus levels is caused by reduced GFR
- phosphorus binds to calcium -> hypocalcemia
- **serum ionized calciu, should be measured
what is the tx for patients who are symptomatically hypocalcemic but whose phosphate levels are very high?
- dialysis
- if you give IV calcium, it may result in deposition of calciu, phosphate into vasculature and organs
- however, give IV calcium while waiting for dialysis if pt has tetany, QT prolongation, Chvostek sign
Name signs/symptoms of severe hypocalcemia
- tetany
- confussion, sz
- Trousseau’s sign
- Chovstek sign
- QT prolongation
patients with serum phosphate levels > 6 mg/dL should be treated with
dietary phosphate binders
- if serum ionized ca2+ is low => calcium acetate or calcium carbonate
- if serum ionized ca2+ is high => aluminum hydroxide
dialysis should be initiated in patients with severe uremia. what are some signs of severe uremia
- pericarditis
- neuropathy
- unexplained decline in mental status
