Acute Renal Failure
Hai Ho, M.D.
What is acute renal failure?
Impairment of kidney function leading to retention of substances normally excreted by the kidney
Hours and days
Epidemiology
Overall mortality rate: 40-50%
Kidney anatomy & physiology
Kidney anatomy & physiology
Compartmentalize causes?
PrenalRenal or intrinsicPostrenal
Pathophysiology of prerenal failure?
Hypoperfusion to the kidney
Common causes of prerenal failure?
HypovolumiaBleedingBurnDehydration from GI loss
HypervolumiaCongestive heart failureThird-spacing – cirrhosis, acute pancreatitis
Peripheral vasodilationSeptic shock
Common cause of intrinsic renal failure?
Acute tubular necrosis – most common cause of acute renal failure in hospitalized patients
Glomerulonephritis – rare, common in children after streptococcal infection
What is acute tubular necrosis?
Disorder resulting from damage of renal tubule cells
What cause acute tubular necrosis?
Prerenal azotemia Ischemia > 30 minutes Most common in hospitalized patients
Rhabdomyolysis Contrast dye Drugs
Aminoglycosides Amphotericin NSAID ACE-inhibitor
Common cause of postrenal failure?
Ureteric obstruction – tumors, stonesBladder outflow obstruction (prostatism)
Clinical presentations of acute renal failure?
AsymptomaticDecreased or no urine outputHypervolumia
Pulmonary edema – tachycardia, tachapneaPeripheral edema
Uremia – lethargy, nausea, anorexiaArrhythmia – hyperkalemia, acidosis
Diagnostic tests
Renal function – GFR Plasma creatinine
May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR
Interesting in the trend rather than absolute value Affect by muscle mass
Creatinine clearance Stable renal function Cockcroft-Gault equation
Cockcroft-Gault equation
(140-age) x lean body weight (kg)
---------------------------------------------
PCr (mg/dL) x 72
Women – multiple by 0.85
Diagnostic tests
Renal function – GFR Plasma creatinine
May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR
Interesting in the trend rather than absolute value Creatinine clearance
Stable renal function Cockcroft-Gault equation
BUN:Cr 15:1 to 20:1 – prerenal, due to increased BUN
absorption 10:1 – cirrhosis or other hypoprotein state
Diagnostic tests
Renal function – GFR Plasma creatinine
May not rise initially due to compensatory hypertrophy and hyperfiltration, therefore not detect actively declining GFR
Interesting in the trend rather than absolute value
Creatinine clearance Stable renal function Cockcroft-Gault equation
Fractional excretion of sodium
Fractional excretion of sodium
UNa x PCr FENa = --------------- x 100
PNa x UCr Interpretation
<1% – prerenal, glomerulonephritis, obstruction >2% – ATN 1-2% - either prerenal or ATN
Not accurate before diuretics or IVF
Diagnostic tests
UrinalysisDipstick – hematuria and proteinuriaMicroscopic examination
RBC cast – glomerulonephritis
RBC cast
Damaged glomerular basement membrane
RBC cast
Diagnostic tests
UrinalysisDipstick – hematuria and proteinuriaMicroscopic examination
RBC cast – glomerulonephritisWBC cast – acute pyelonephritis
WBC cast
Diagnostic tests
UrinalysisDipstick – hematuria and proteinuriaMicroscopic examination
RBC cast – glomerulonephritisWBC cast – infection such as pyelonephritisGranular cast – protein aggregate or
degenerative cellular casts as in acute tubular necrosis
Granular cast
Granular cast
Diagnostic tests
Urinalysis Dipstick – hematuria and proteinuria Microscopic examination
RBC cast – glomerulonephritis WBC cast – infection such as pyelonephritis Granular cast – protein aggregate or degenerative cellular
casts as in acute tubular necrosis Positive blood on dipstick but negative RBC on microscopic
exam - rhadomyolysis
Renal ultrasound
Renal ultrasound?
Obstruction – hydronephrosisChronic disease – atrophic kidney
Renal biopsy
Selective cases such as glomerulonephritis, vasculitis, nephrotic syndrome
Treatment?
Treat the underlying causePrerenal – increase perfusionIntrinsic – if possible, remove the culpritPostrenal – relieve the obstruction
General management
Hyperkalemia – low K diet, lasix, insulin/glucose, NaHCO3, Kayexalate, Ca gluconate
Fluid retention and overload – diuresis, fluid restriction
Diet – low protein, high carbohydrates Acetylcysteine with 0.45% NS with contrast
study – reduce nephropathy Dialysis
References
Acute tubular necrosis. http://www.nlm.nih.gov/medlineplus/ency/article/000512.htm
Acute renal failure http://www.firstconsult.com/
http://www.supermt.com.tw/URNfiles/image/CASTS/RBCCAST/RBC%20cast.htm