AKI

Definition: daily increase in Cr (>0.5-1.5 per day) or BUN (>10-20/day)

Urine: UA, sodium, creatinine, osmolality, urea
Plasma: sodium, creatinine, osmolality, BUN, Na, K, Phos, Calcium, CBC, eosinophils, peripheral smear
Additional testing (if needed): Complement (C3, C4), ASO titers, ANA, ANCA
Imaging: renal US with doppler flow, voiding cystourethrography (postrenal), radionucline renal scanning (transplant, obstruction), CXR (pulmonary edema), ECHO (heart failure patient)
Other: ECG

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3 Clinical Patterns:

• Prerenal
• Intrinsic
• Postrenal

2 output states

• Oliguric: urine volume < 400mL/day; worse pregnosis unless it is prerenal; anuria < 100 mL/day
• Non-Oliguric

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Causes:

Prerenal

• Volume depeletion
  • renal losses (diuretics, polyuria)
  • GI losses (vomiting, diarrhea)
  • Cutaneous losses (burns, SJS)
  • Hemorrhage
  • Pancreatitis
• Decreased cardiac output
  • CHF
  • PE
  • AMI
  • Valvular disease
  • abdominal compartment syndrome
• Systemic vasodilation
  • sepsis
  • anaphylaxis
  • anesthetics
  • drug overdose
• afferent arteriolar vasoconstriction
  • hypercalcemia
  • drugs (NSAIDS, ampho B, norepinephrine, radiocontrast agents)
• efferent arteriolar vasodilation
  • ACEi, ARB

Intrinsic

• Vascular (large and small vessel)
  • renal artery obstruction (thrombosis, emboli, dissection, vasculitis)
  • renal vein obstruction (thrombosis)
  • Microangiopathy (TTP, HUS, DIC, preeclampsia)
  • Malignant HTN
  • Scleroderma renal crisis
  • Transplant rejection
  • atheroembolic disease
• Glomerular
  • anti-glomerular basement membrane (Goodpastures)
  • ANCA-associated glomerular nephritis (Wegener, Churg-Strauss, Microscopy poly angiitis)
  • Immune complex GN (lupus, post-infectious, cryoglobulinemia, primary membranoproliferative GN)
• Tubular
  • Ischemic
  • Cytotoxic (rhabdo, intravascular hemolysis)
  • Crystals (tumor lysis, seizures, ethylene glycol, megadose Vitamin C, acyclovir, indinivir, MTX)
  • Drugs (immunoglycosides, lithium, ampho B, pentamidine, cisplatin, ifosfamide, radiocontrast agents)
• Interstitial
  • Drugs (PCN, cephalosporin, NSAIDs, PPI, allopurinol, rifampin, indinivir, mesalamine, sulfonamides)
  • Infection (pyelo, viral nephritides)
  • Systemic Disease (sjogren, sarcoid, lupus, lymphoma, leukemia, tubulonephritis, uveitis)

Post Renal

• Ureteral Obstruction (stones, tumor, fibrosis, ligation during pelvic surgery)
• Bladder neck obstruction (BPH, prostate CA, neurogenic bladder, TCA, bladder tumor, stone disease, hemorrhage/clot)
• Urethral obstruction (stricture, tumor, phimosis)

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History

• Hypotension
• Volume Contraction
• CHF
• Nephrotoxic drugs
• Trauma, unaccustomed exertion
• Blood loss, transfusions
• Connective tissue or autoimmune disorders
• Toxins, ethyl alcohol, ethylene glycol
• Oliguria favors AKI
• Abrupt anuria: consider postrenal, renal embolism, severe glomerular nephritis

PMHx (increasing risk of AKI)

• HTN
• DM
• CHF
• Multiple Myeloma
• Chronic infection
• Myeloproliferative Disorder

Physical Exam

• Skin: purpura, petechiae, echymosis, livedo reticularis - inflammatory or vascular causes
• signs of TTP, DIC, embolic phenomena
• Eyes: Uveitis - interstitial nephritis, necrotizing vasculitis
• Ocular palsy - ethylene glycol poisoning, necrotizing vasculitis
• Fundoscopic Exam - e/o severe HTN, atheroembolic phenomena, endocarditis
• Cardiovascular System: volume status, VS including I+O, JVP, heart, lungs, skin turgor, mucous membranes, peripheral edema - CHF, severe HTN (renovascular disease, glomerular nephritis, vasculitis, atheroembolic disease(
• Abdomen: signs of outlet obstruction postrenal; epigastric bruit renovascular HTN

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Lab Studies

BUN/Cr

• ratio BUN/Cr > 20:1 prerenal
• BUN may be elevated in GI bleed, mucosal bleeding, steroid, protein loading
• if serum creatine rises greater than 1.5 mg/dL/day, must r/o rhabdomyolysis

CBC

• anemia: due to dilution and decrease eryhthropoiesis
• microangiopathic hemolytic anemia with schistocytes and thrombocytopenia: indicates HUS (hemolytic uremic syndrome)
• oliguria + neutropenia and thrombocytopenia: consider SLE
• eosinophilia: allergic interstitial nephritis
• Schistocytes - HUS/TTP
• rouleaux formation - multiple myeloma, consider SPEP, UPEP
• myoglobin, free hemoglobin, uric acid

Other serology

• complement testing: decreased c3, c4; acute post-streptococcal glomerulonephritis, lupus nephritis, membranoproliferative glomerulonephritis
• elevated ASO: confirms Acute PSGN
• ANA: suggests lupus
• ANCA: suggests vasculitis

UA:

• few hyaline, fine granular casts; little protein, heme, red cells: prerenal
• heme postive urine with no red cells: rhabdomyolysis or hemolysis
• hematuria, proteinuria: intrinsic renal failure (glomerular, interstitial)
• brown granular casts: intrinsic renal failure, ischemic or toxic ATN
• red cell casts: intrinsic, acute glomerular nephritis
• RBCs
  • Eumorphic: bleeding along the collecting system
  • Dysmorphic: glomerular nephritis
• white cells, white cell casts, eosinophilia: intrinsinc, interstitial nephritis
• eosinophilia: allergic interstitial nephritis, but can also be seen in UTI, glomerulonephritis, atherembolic disease
• oxalate crystals: ATN

Urinary Indices

• Comparine urine and serum creatinine, sodium, osmolality
• resorptive capacity of tubular cells and concentrating ability is preserved in prerenal conditions
• these functions are impaired in instrinsic renal failure due to structural damage
• Be careful with urinary indices; serum and urine indices should be checked prior to fluids, diuretics, mannitol; urine should be free of glucose, contrast, myoglobin

Urine Indices and Prerenal failure

• Specific gravity is high: >1.020; (able to concentrate urine)
• urine: plasma creatinine ratio > 40 (dumping creatinine)
• urine: plasma osmolality high ratio >1.5 (concentrating urine)
• urine sodium low < 20 mEq/L (resorption of Na to preserve intravascular volume)
• FENa, the percentage of filtered sodium that is excreted, is low < 1% (resorption capacity intact)
  • only useful for AKI with Oliguria
  • valuable indicator of functioning renal tubules
• be careful; urine indices suggestive of prerenal may in fact be early glomerulonephritis, vasculitis, vascular occlusion, early postrenal failure, contrast nephropathy, rhabdomyolysis; FENa may be falsely elevated in urine high in prerenal failure with high excretion of ketones and glucose
• FEurea, the percentage of filtered urea that is excreted; helpful with patients on diuretics; urea transport not affected

Urine Indices and Intrinsic failure

• Specific gravity is low < 1.020 (unable to concentrate urine)
• urine: plasma creatinine ratio < 20 (unable to dump creatinine)
• urine: plasma osmolality low< 1.1 (unable to concentrate urine)
• urine sodium is high > 40 (unable to reabsorb Na)
• FENa, the percentage of filtered sodium that is excreted, is high >2% (resorption capacity impaired)

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Therapy

• mainly supportive
• minimize further damage, discontinue renotoxic medications
• maintain volume homeostasis
• furosemide plays a role in treating volume overload; it has no role in converting an oliguric AKI to non-oliguric AKI although response to furosemide may be a good prognostic sign
• correct acidosis
• correct hyperkalemia
• correct hematologic abnormalities