Acute Renal Failure ARF

Definition (jama 2003:289:747 Loocrt 200S:365:417)

• ARF: T Cr :0.5 mg dl or T Cr --20% if baseline Cr -2.5 mg dl in - 2 wks

• Oliguria: UOP 100-400 ml 24 h; anuria: UOP 100 ml 24 h

Workup

• History and physical: recent procedures and medications, vital signs, volume status.

signs and symptoms of obstruction, vascular disease or systemic disease

• Urine evaluation: output, urinalysis, sediment, electrolytes and osmolality

• Fractional excretion of sodium (FEn>) (Uni Pn») (Uo Per)

<1% — prerenal, contrast, or glomerulonephritis; >2% — ATN In setting of diuretics. ✓ FEun (Uun Pun) (Uo Per); <35% prerenal

• Renal U S: r o obstruction & eval kidney size to estimate chronicity of renal failure

• Serologies (if indicated): see "Glomerular Disease"

• Renal biopsy: may be necessary if cause remains unclear

Etiologies and Diagnosis of Acute Renal Failure

Etiologies

U/A, Sediment, Indices

Prerenal

i Effective arterial volume

Hypovolemia

Decreased cardiac contractility (eg. CHF) Systemic vasodilatation (eg. sepsis) Renal vasoconstriction NSAIDs.ACEl ARB (i intraglomerular pressure), calcineurin inhibitors, hepatorenal, hypercalcemia Large vessel: RAS (bilateral + ACEI). thrombosis, embolism, dissection, vasculitis

Bland

Transparent hyaline casts FEn, <")% BUN Cr >20

Intrinsic

Acute tubular necrosis (ATN)

Ischtmio: progression of prerenal disease Toxins

Drugs: AG. amphotericin, cisplatin Pigments: myoglobin, hemoglobin Proteins: Ig light chains Contrast-induced ARF (OARF): i RBF + toxin Acute interstitial nephritis (AIN) Allergic: p-lactams, sulfa drugs. NSAIDs Infection: pyelonephritis Infiltrative: sarcoid, lymphoma, leukemia

Pigmented granular "muddy brown" casts in 75% (• in CIARF)

• RBCs & protein from tubular damage

WBCs.WBC casts. • RBCs © eos in abx © lymphs in NSAIDs

Small vessel: cholesterol emboli, thrombotic microangiopathy (HUS TTP. DIC. preeclampsia, malignant HTN. scleroderma renal crisis)

i RBCs

© eos in cholesterol emboli

Glomerulonephritis (see "Glomerular Disease")

Dysmorphic RBCs & RBC casts

Postrenal

Bladder neck: BPH. prostate cancer, neurogenic bladder, anticholinergic meds Ureteral: malig. LAN. retroperitoneal fibrosis.

bilateral nephrolithiasis Tubular precipitation of crystals

Bland

- RBCs if nephrolithiasis

Contrast-induced acute renal failure (CIARF)

• Risk factors: CKD. DM. CHF. age. hypotension. T contrast volume (jacc 2004:44:1393)

• Clinical: Cr T w in 24 h. peaks in 3-5 d. resolves in 7-10 d

• Prevention (NEJM 2006:354 379. jama 2006.295 276S. Circ 2006:113:1799)

N-acetylcysteine 600 mg PO bid on day prior to and day of contrast (Lancet 2003362598) Pre/post-hydration (NLjm 1994:331 1416) unless contraindication to IVF (eg. CHF) isotonic NaHCOs: 3mL kg h x 1 h before. 1 mL kg h x 6 h after (jama 2004:291.2328) benefit additive to N-acetylcysteine (6rt 2007:115:1211) Hold ACEI/ARB. NSAIDs. diuretics

Minimize contrast volume and consider isosmolar contrast (jacc 2006:48 692) ? Higher NAC dose (1200 mg IV) in acute Ml undergoing PCI (nejm 2006:354 2773) ? Hemofiltration (before & for 24 h after) if Cr >2.0 (nejm 2003:349:1333)

• Gadolinium: can be cause of ARF in CKD (Ncph DiaiTnms 2006:21:697)

prevention measures listed above for iodinated contrast are of no proven benefit

Treatment

• Treat underlying disorder (see relevant sections); consider steroids if AIN

• Avoid nephrotoxic insults; review dosing of renally cleared drugs

• Optimize hemodynamics (both MAP & CO)

• Watch for and correct volume overload, electrolyte (T K. T PO4). & acid base status

• If obstruction is diagnosed and relieved, watch for:

Hypotonic diuresis (2° buildup of BUN. tubular damage); Rx with IVF (eg. 1/2 NS) Hemorrhagic cystitis (rapid A in size of bladder vessels); avoid by decompressing slowly

• Indications for urgent dialysis (when condition refractory to conventional therapy)

Acid-base disturbance: acidemia

Electrolyte disorder: generally hyperkalemia: occasionally hypercalcemia, tumor lysis

Intoxication: methanol, ethylene glycol, lithium, salicylates

Overload of volume (CHF)

Uremia: pericarditis, encephalopathy, bleeding

• No benefit to dopamine (awwfi 2005:142^10). diuretics <;ama 2002.288 2 547). or mannitol

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