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?
Prenal
 Renal or intrinsic
 Postrenal

Pathophysiology of prerenal
failure?
Hypoperfusion to the kidney
Common causes of prerenal failure?

Hypovolumia
Bleeding
 Burn
 Dehydration from GI loss


Hypervolumia
Congestive heart failure
 Third-spacing – cirrhosis, acute pancreatitis


Peripheral vasodilation

Septic 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, stones
 Bladder outflow obstruction (prostatism)

Clinical presentations of acute renal
failure?
Asymptomatic
 Decreased or no urine output
 Hypervolumia

Pulmonary edema – tachycardia, tachapnea
 Peripheral edema

Uremia – lethargy, nausea, anorexia
 Arrhythmia – 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



Creatinine clearance



May not rise initially due to compensatory hypertrophy and
hyperfiltration, therefore not detect actively declining GFR
Interesting in the trend rather than absolute value
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



Creatinine clearance



May not rise initially due to compensatory hypertrophy and
hyperfiltration, therefore not detect actively declining GFR
Interesting in the trend rather than absolute value
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

Urinalysis
Dipstick – hematuria and proteinuria
 Microscopic examination


RBC cast – glomerulonephritis
RBC cast
Damaged glomerular
basement membrane
RBC cast
Diagnostic tests

Urinalysis
Dipstick – hematuria and proteinuria
 Microscopic examination

RBC cast – glomerulonephritis
 WBC cast – acute pyelonephritis

WBC 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

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 – hydronephrosis
 Chronic disease – atrophic kidney

Renal biopsy
Selective cases such as
glomerulonephritis, vasculitis,
nephrotic syndrome
Treatment?
Treat the underlying cause
 Prerenal – increase perfusion
 Intrinsic – if possible, remove the culprit
 Postrenal – 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/ima
ge/CASTS/RBCCAST/RBC%20cast.htm
