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