091. Acute Renal Failure

General

3 types: pre-renal (decreased blood flow), intrinsic (renal parenchyma insult) and post-renal (obstructed renal outflow). In the community, pre-renal is the most common cause usually secondary to volume depletion.

Normal GFR for child is >120, decreases by 8 every decade. Lower muscle mass (women, elderly) leads to lower baseline creatinine.

Acute renal failure usually asymptomatic until severe uremia: nausea/vomiting, drowsiness, fatigue, confusion, coma.

Renal US is the imaging study of choice initially. Can be down bedside in the ED. If seeing hydronephrosis, likely need non contrast CT to look for where and what is the obstruction.

Pre-Renal

Tubular/glomerular function maintained. Usually presents with thirst, orthostasis, lightheadedness, decreased urine output.

Causes include hypovolemia (N/V/D, burns), hypotension from hemorrhage, decreased cardiac output (MI, cardiomyopathy, anti-HTN medications, nitrates). Prlonged pre-renal failure can cause ATN.

BUN/Cr ratio > 20, though not specific/sensitive. Also look for increased urine specific gravity. FeNa: Una/Pna x Ucr/Pcr. Usually < 1% in pre-renal. Limitations as well. Also have hyaline casts.

CHF/cirrhosis: can have volume overload but have intra-arterial volume loss. Diuretcs may worsen renal failure and volume loss.

Treatment: IVF, augment cardiac output.

Intrinsic

Disease of glomeruli, intrarenal vasculature, interstitium. Most common cause is ATN (acute tubular necrosis), also sometimes called acute kidney injury. Due to ischemia from cardiac arrest, sepsis, hypotension, trauma/surgery.

Check urine and urine electrolytes. Look for granular casts.

Acute glomerulonephritis: hematuria, proteinuria and RBC casts. Dark urine + edema along with fever, malaise, rash.

Pulmonary-renal syndromes: Goodpasture, Wegeners – cough, SOB, hemoptysis.

Radiocontrast-induced nephropathy: increasing creatinine over 3-5 days with usually complete resolution. Need to consider not doing IV contrast with GFR < 60.

Acute interstitial nephritis: usually due to drug (PCN, diuretics, NSAIDs) and infection. Rash, fever, eosinophilia and proteinuria. Treat underlying cause.

Post-Renal

Usually secondary to BPH or functional bladder neck obstruction (neurogenic bladder).

Renal US initially, then non contrast CT to look for cause of obstruction.

Post-obstructive diuresis can result in significant volume loss. Usually with prolonged obstruction. If output is >250mL/hr for >2 hrs, may need to consider admission.

Questions

 

References/Resources

Tintinalli, Seventh Edition, Chapter 91: Acute Renal Failure

Rosens, Chapter 87: Renal Failure

091. Acute Renal Failure