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31 derebail acute renal failure

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  • 1. Acute Renal Failure for the Intern Things to think about before you call that consult… Vimal Derebail, MD Renal Fellow UNC Division of Nephrology and Hypertension
  • 2. Acute Renal Failure
    • Is it common enough for me to worry about?
    • Of course…
      • 1% of all hospital admissions.
      • 10-30% of all ICU admissions.
    • Is it really all that bad?
      • Mortality in all hospitalizations increases.
      • If dialysis requiring, approaches 40-90%.
  • 3. Acute Renal Failure
    • Approach to acute renal failure…
    • Classifying the cause:
      • PreRenal (30%).
      • IntraRenal/Intrinsic cause (65%).
      • PostRenal (5%).
  • 4. Acute Renal Failure
    • Pre-Renal
    • Think of it as anything that reduces renal perfusion – i.e. altered hemodynamics.
      • Volume depletion.
      • Hypotension.
      • Cardiovascular (CHF, arrythmias).
      • Intrarenal vasoconstriction.
        • ACE-I, NSAIDs (inhibit prostaglandin), Ampho B, cyclosporine/tacrolimus, radiographic contrast.
      • Hypercalcemia
      • Hepatorenal syndrome.
  • 5. Acute Renal Failure
    • IntraRenal/Intrinsic Causes
      • Vascular – renal infarct, cortical necrosis, renal vein thrombosis, malignant HTN, scleroderma renal crisis, atheroemboli.
      • Tubular injury – ischemic or nephrotoxic.
      • Glomerular – acute GN, vasculitides, TMA.
      • Interstitial damage – tumor infiltration, medication (Acute interstitial nephritis).
  • 6. Acute Renal Failure
    • Post-Renal Causes
    • Obstruction…
      • Prostatic hypertrophy.
      • Neurogenic bladder.
      • Intraureteral obstruction – stones, tumor, clot, crystals.
      • Extraureteral obstruction – extrinsic tumors, retroperitoneal fibrosis.
  • 7. Acute Renal Failure
    • Nonoliguric v. Oliguric v. Anuric.
    • What does this mean and why does this matter?
    • Oliguric renal failure.
      • Functionally, urine output less than that required to maintain solute balance (can’t excrete all solute taken in).
      • Defined as urine output < 400ml/24hr.
    • Anuric renal failure.
      • Defined as urine output < 100ml/24hr.
      • Less common – suggests complete obstruction, major vascular catastrophy, or more commonly severe ATN.
  • 8. Acute Renal Failure
    • Again, why does this matter?
    • Classifying by urine output may help establish a cause.
      • Oliguria – more common with obstruction, prerenal azotemia
      • Nonoliguric – intrarenal causes – nephrotoxic ATN, acute GN, AIN.
    • More importantly, assists in prognosis.
      • Significantly higher mortality with oliguric renal failure.
      • Approaches 80% in some series.
      • Nonoliguric renal failure may also suggest greater liklihood of recovery of function.
  • 9. Acute Renal Failure
    • So where do I start?
    • First question, is it really all acute?
    • Difficult to know by labs alone.
    • Clues to chronic disease
      • Pre-existing illness – DM, HTN, age, vascular disease.
      • Uremic symptoms – fatigue, nausea, anorexia, pruritis, altered taste sensation ( dysgeusia ), hiccups ( singultus ).
      • Small, echogenic kidneys by ultrasound.
  • 10. Acute Renal Failure
    • Yes – it’s acute.
    • So what’s next?
    • The history, of course…
      • Identify an insult
        • Volume depletion (diarrhea, blood loss, emesis, over-diuresis), Hypotension, CHF.
        • Drug exposure – toxin or reduction of renal perfusion.
        • Contrast exposure.
        • Infections – inflammatory mediators v. direct infection
        • Endogenous toxins/insults – myoglobin,hemoglobin, uric acid.
  • 11. Acute Renal FAilure
    • Symptoms:
      • Fever, rash, joint pains, myalgias
        • Concern for SLE, vasculitis, acute interstitial nephritis.
      • Dyspnea – heart failure.
      • Hemoptysis – Goodpasture’s, Wegener’s.
      • Preceding bloody diarrhea – HUS.
      • Preceding pharyngitis – post-Strep GN, post-infectious GN.
  • 12. Acute Renal Failure
    • Urine output.
      • Abrupt anuria.
        • Acute obstruction, severe acute GN, sudden vascular catastrophe.
      • Slowly diminishing.
        • Ureteral stricture.
        • Prostatic enlargement.
      • Presence of hematuria
        • Painless – suggests GN.
        • Painful – suggest ureteral obstruction.
  • 13. Acute Renal Failure
    • Physical Exam.
      • Skin – new rashes.
        • Livedo reticularis – atheroemboli, SLE, cryoglobulins.
        • Petechiae – HSP.
        • Malar rash – SLE.
      • Exe
        • Papilledema – malignant HTN.
        • Roth’s spots – endocarditis.
      • CV
        • Rub – suggestive of uremic pericarditis, lupus.
        • Gallop – suggesting CHF.
  • 14. Acute Renal Failure
    • Physical Exam.
      • Assessing volume status.
        • Is the patient intravascularly volume depleted?
          • Neck veins – JVP
          • Peripheral edema or lack of.
          • Orthostatic vitals.
      • Not always straightforward.
      • Pt. may be edematous (low albumin) or have significant right sided heart disease.
  • 15. Acute Renal Failure
    • Diagnostic studies.
    • BUN/Creatinine ratio.
      • > 20:1 – suggest prerenal or obstruction.
      • Can be elevated by anything leading to increased urea production/absorption.
        • GI bleed
        • TPN
        • Steroids
        • Drugs – Tigecycline.
    • Creatinine in anephric state typically only rises 1mg/dl/day.
      • If greater – should be concerned for rhabdomyolysis.
  • 16. Acute Renal Failure
    • Urine Electrolytes
    • FE Na – fractional excretion of sodium.
      • FE Na = Urine Na x Plasma Cr
            • X 100.
            • Urine Cr x Plasma Na.
  • 17. Acute Renal Failure
    • FE Na
      • < 1% suggestive of prerenal cause.
      • > 2% suggestive of ATN/tubular damage.
      • Not quite so clear cut – low FE Na seen in other causes of renal failure.
        • Nonoliguric ATN.
        • Radiocontrast nephropathy.
        • Acute GN.
        • Acute interstitial nephritis.
      • Not as helpful in setting of diuretics.
        • Can use FE Urea
        • < 35% suggests prerenal cause.
  • 18. Acute Renal Failure <20 >40 Urine Cr ./Plasma Cr. ≤ 20:1 >20:1 BUN/Creatinine >50% <35% FE Urea ≥ 1% <1% FE Na >40 mEq/L <20 mEq/L Urine Na ATN Pre-Renal Index
  • 19. Acute Renal Failure
    • SPEP/UPEP
    • ANA
    • ANCA
    • Hepatitis B and C
    • HIV
    • Uric Acid
    • Cryoglobulins
    • Complement levels (C3, C4)
    • CK
    • Peripheral smear
    Other Labs we like to order…
  • 20. Acute Renal Failure
    • Imaging…
      • Renal U/S – we ALWAYS like to see one.
        • Rules out obstruction.
        • Evaluates chronicity – small size, echogenic.
        • Makes sure there are 2 kidneys.
      • MRA or Doppler U/S may be useful in looking for renal artery stenosis.
  • 21. Acute Renal Failure
    • Don’t forget the urine sediment!
    • Can be helpful in identifying underlying disease states (proteinuric disease, underlying chronic GN) as well as examining acute insult.
  • 22. Acute Renal failure
    • Introduction to casts…
    Hyaline Casts: Better seen with low light. Non-specific. Composed of Tamm-Horsfall mucoprotein.
  • 23. Acute Renal Failure UpToDate Images. Waxy Casts: Smooth appearance. Blunt ends. May have a “crack”. Felt to be last stage of degenerating cast – representative of chronic disease. Granular Casts: Represent degenerating cellular casts or aggregated protein. Nonspecific.
  • 24. Acute Renal Failure Fatty Casts: Seen in patients with significant proteinuria. Refractile in appearance. May be associated with free lipid in the urine. Can see also “oval fat bodies” – RTE’s that have ingested lipid. Polarize – demonstrate “Maltese cross”. UpToDate Images.
  • 25. Acute Renal Failure Muddy Brown Casts: Highly suggestive of ATN. Pigmented granular casts as seen in hyperbilirubinemia can be confused for these. UpToDate Images.
  • 26. Acute Renal Failure UpToDate Images. White Blood Cell Casts: Raises concern for interstitial nephritis. Can be seen in other inflammatory disorders. Also seen in pyelonephritis.
  • 27. Acute Renal Failure
    • Hematuria
    Nonglomerular hematuria: Urologic causes. Bladder/Foley trauma. Nephrolithiasis. Urologic malignancy. May be “crenated” based upon age of urine, osmolality – NOT dysmorphic.
  • 28. Acute Renal Failure Red Blood Cell Casts: Essentially diagnostic of vasculitis or glomerulonephritis. Dysmorphic Red Cells: Suggestive of glomerular bleeding as seen with glomerulonephritis. Blebs, buds, membrane loss. Rarely reported in other conditions – DM, ATN.
  • 29. Acute Renal Failure Crystals – Pretty and important. Uric acid crystals: Seen in any setting of elevated uric acid and an acidic urine. Seen with tumor lysis syndrome. Calcium oxalate crystals: Monohydrate – dumbell shaped, may be needle-like. Dihydrate – envelope shaped. Form independent of urine pH. Seen acutely in ethylene glycol ingestion. UpToDate Images.
  • 30. Acute Renal Failure
    • Prerenal Azotemia
      • Decreased renal blood flow – usually with afferent arteriolar vasoconstriction.
      • Bland urine sediment – may see hyaline casts.
      • Low FENa, high BUN/Cr. Ratio.
      • Tx – volume repletion, inotropes in CHF.
  • 31. Acute Renal Failure
    • ATN
      • Usually after ischemic, toxic insult.
      • Tubular necrosis leads to sloughing of tubular cells into the lumen leading to obstruction of flow.
      • Sediment – RTE’s, granular casts.
      • Classic “muddy brown casts”.
      • FENa >2% typically.
      • Treatment – correcting underlying cause if possible, otherwise supportive.
  • 32. Acute Renal Failure
    • Glomerulonephritis
      • Always think about this at UNC.
      • Several forms – ANCA, cell mediated, Ab associated, Immune complex mediated (SLE).
      • Dysmorphic hematuria, RBC casts.
      • Some degree of proteinuria.
  • 33. Acute Renal Failure
    • Acute Interstitial Nephritis
      • Typically rapid decline in function.
      • May have associated fever, rash, arthralgias.
      • Peripheral eosinophlia.
      • Hansel’s stain for urine may be helpful.
      • Urine sediment – Wbc’s and/or wbc casts.
      • Tx – removal of offending agent, +/- steroids.
  • 34. Acute Renal Failure
    • Rhabdomyolysis
      • Causes – trauma, exertion, medications, hypoxemia, hereditary disorders.
      • Treatment
        • Aggressive hydration
        • Alkalinazation/mannitol controversial.
        • May see hyperkalemia, hypocalcemia.
  • 35. Acute Renal Failure
    • Cholesterol Emboli
      • Risk factors:
        • Aortic surgery.
        • Angiography, cardiac catheterization.
        • Balloon pump.
        • Thrombolytics.
      • Peripheral eosinophilia.
      • Livedo reticularis.
      • Hypocomplementemia.
  • 36. Acute Renal Failure
    • Drugs:
      • Prerenal – cyclosporine, tacrolimus, contrast, ACE-I, ampho B, NSAIDs.
      • ATN – AG’s, ampho B, cisplatin
      • AIN – PCN, cephalosporins, sulfa drugs, rifampin, NSAIDs, interferon, quinolones.
      • Post-Renal – acyclovir, indinavir, analgesics.
  • 37. Acute Renal Failure
    • Contrast Nephropathy.
      • Risk factors
        • DM.
        • Pre-existing renal disease.
        • Severe CHF.
        • Volume depletion.
        • Myeloma.
        • Elderly.
        • Contrast volume.
        • Coadministration of other nephrotoxin.
  • 38. Acute Renal Failure
    • Contrast nephropathy.
      • Prevention – volume expansion – isotonic saline v. bicarbonate
      • NAC, theophylline less convincing.
      • Hemofiltration studied – impractical, poor evidence.
  • 39. Acute Renal Failure
    • Hepatorenal syndrome – major criteria.
      • Chronic or acute liver disease with advanced hepatic failure and portal hypertension
      • Low GFR, as indicated by a serum creatinine >1.5 mg/dL or a creatinine clearance < 40 mL/min
      • Absence of shock, ongoing bacterial infection, fluid loss, and current or recurrent treatment with nephrotoxic drugs. Absence of gastrointestinal fluid losses (repeated vomiting or intense diarrhea) or renal fluid losses (as indicated by weight loss > 500 gm/d for several days in patients with ascites without peripheral edema or > 100 gm/d in patients with peripheral edema)
      • No sustained improvement in renal function (decrease in serum creatinine to 1.5 mg/dL or less or increase in creatinine clearance to 40 ml/min or more) after withdrawal of diuretics and expansion of plasma volume with 1.5 L of isotonic saline
      • Proteinuria < 500 mg/d and ultrasonographic evidence of obstructive uropathy or parenchymal renal disease.
  • 40. Acute Renal Failure
    • Hepatorenal Syndrome – minor criteria.
      • Urine volume < 500 mL/day
      • Urine sodium < 10 mEq/L
      • Urine osmolality > plasma osmolality
      • Urine red blood cells < 50 per high-power field
      • Serum sodium concentration < 130 mEq/L
  • 41.