DESCRIPTION

• The disorder is now known as acute kidney injury (AKI); the term renal failure is outdated.
• Changes in glomerular filtration rate (GFR) and urine output (UO) encompassing a spectrum ranging from normal physiologic response to end-stage renal disease (ESRD) and measured by accumulation of nitrogenous by-products.
• Defined by the RIFLE criteria:
  • 3 stages of renal injury:
    • Risk: Increased creatinine (Cr) ×1.5 or GFR decrease > 25%, UO < 0.5 mL/kg/h × > 6 h
    • Injury: Increased Cr ×2 or GFR decrease > 50%, UO < 0.5 mL/kg/h × > 12 h
    • Failure: Increased Cr ×3 or GFR decrease > 75% or Cr ≥4 mg/dL (acute rise of ≥0.5 mg/dL), UO < 0.3 mL/kg/h × 24 h or anuria × 12 h
  • 2 stages of outcome:
    • Loss: Loss of renal function > 4 wk
    • ESRD: Loss of renal function > 3 mo
• The most severe marker defines stage.
• AKI based upon changes within last 48h; however, must often base on most recent data.
• Higher RIFLE stages correlate with higher 1 and 6 mo mortality rates for hospitalized patients.

ETIOLOGY

• Prerenal AKI:
  • Caused by renal hypoperfusion
  • Renal tissue remains normal unless severe/prolonged hypoperfusion.
• Intrarenal AKI:
  • Caused by diseases of the renal parenchyma
• Iatrogenic AKI causes include:
  • Aminoglycoside antibiotics
  • Radiocontrast material administration
  • NSAIDs
  • ACE inhibitors
  • Angiotensin receptor blockers
• Postrenal AKI:
  • Due to urinary tract obstruction (e.g., prostatic hypertrophy, prostatitis)

[Outline]

• DESCRIPTION
• ETIOLOGY

SIGNS AND SYMPTOMS

Acute Kidney Injury

• Often asymptomatic and commonly diagnosed with incidental lab findings
• Oliguria (< 400 mL/d urine production)
• Fluid overload:
  • Dyspnea
  • Hypertension
  • Jugular venous distention
  • Pulmonary and peripheral edema
  • Ascites
  • Pericardial and pleural effusion
• Nausea/vomiting
• Pruritus/skin changes
• Confusion/mental status changes

Prerenal AKI

• Absolute or relative volume deficit
• Dry mucous membranes
• Hypotension
• Tachycardia
• Low cardiac output
• Congestive heart failure
• Systemic vasodilation (e.g., sepsis, anaphylaxis)

Intrinsic AKI

• Allergic Interstitial Nephritis:
  • Fever
  • Rash
  • Recent myocardial infarction
• Renal vein thrombosis:
  • Nephrotic syndrome
  • Can be associated with pulmonary embolus
  • Flank or abdominal pain
• Glomerulonephritis, vasculitis
• Hemolytic uremic syndrome (HUS)
• Thrombotic thrombocytopenic purpura (TTP):
  • Mild elevation of BUN/Cr
  • Fever
  • Altered mental status
  • Anemia & thrombocytopenia
  • Neurologic: Coma, seizure, headache, altered mental status
• Allergic interstitial nephritis fever:
  • Rash
  • Arthralgias

Postrenal AKI

• Abdominal or flank pain
• Distended bladder
• Oliguria or anuria

Complications of AKI

• Uremic syndrome:
  • Altered mental status
  • Asterixis
  • Reflex abnormalities
  • Focal neurologic abnormality
  • Seizures
  • Restless leg syndrome
  • Pericarditis
  • Pericardial effusion/cardiac tamponade
  • Ileus
  • Platelet dysfunction
  • Pruritus
• Hematologic disorders:
  • Anemia
  • Increased bleeding time & platelet dysfunction
  • Leukocytosis

History

• Prior history of AKI
• Medication history including nephrotoxins
• Weight change

Physical Exam

• Mental status changes/confusion
• Eyes: Fundoscopy
• CV exam: Jugular venous distention, S3
• Lungs: Rales, crackles
• Abdomen: Flank tenderness, palpable kidneys
• Edema
• Skin changes

Geriatric Considerations

• Prone to prerenal AKI
• Cr will vary by body mass index, so a "normal" range in elderly may represent an elevation.
• Increased risk of contrast- and medication-induced AKI

Pediatric Considerations

• Prerenal AKI a concern in neonates
• Anatomic abnormalities

Pregnancy Considerations

• Intrinsic renal azotemia
• Pre-eclampsia/eclampsia
• Ischemia: Postpartum hemorrhage, abruptio placentae, amniotic fluid embolus
• Direct toxicity of illegal abortifacients
• Postpartum TTP, HUS

ESSENTIAL WORKUP

• Electrolytes including Ca, Mg, PO₄
• BUN/Cr
• Urinalysis (UA):
  • Centrifuged specimen helps to distinguish different etiologies of AKI.
  • Exam for casts, blood, WBCs, and crystals
• Fractional excretion (FE) of Na and/or urea
• CBC: Anemia common with chronic disease
• Postvoid residual volume (> 100 mL suggests obstruction) OR
• Ultrasound to rule out obstruction—especially in older men (e.g., prostatic hypertrophy, prostatitis)
• ECG

DIAGNOSIS TESTS & INTERPRETATION

Lab

Prerenal

UA:

• Specific gravity > 1.018
• Osmolality > 500 mmol/kg
• Sodium < 10 mmol/L
• Hyaline casts
• BUN/Cr ratio > 20
• FE_NA < 1%
• Rapid recovery of renal function when renal perfusion normalized

Intrarenal

• BUN/Cr ratio < 10–15
• FE_NA > 2%
• Glomerulonephritis, vasculitis:
  • UA with red cell or granular casts
  • Complement and autoimmune antibodies
• HUS or TTP:
  • UA normal
  • Anemia
  • Thrombocytopenia
  • Schistocytes on blood smear
• Nephrotoxic acute tubular necrosis (ATN):
  • UA:
    • Brown granular or epithelial cell casts
    • Specific gravity = 1.010
    • Urine osmolality < 350 mmol/kg
    • Urine Na > 20 mmol/L
• Ethylene glycol ingestion:
  • UA: Calcium oxalate crystals
  • Anion gap metabolic acidosis
  • Osmolar gap
• Rhabdomyolysis:
  • Elevated serum K⁺, PO₄, myoglobin, creatine phosphokinase, uric acid
  • Decreased serum Ca²⁺
• Tubulointerstitial disease
• Allergic interstitial nephritis:
  • UA with WBC casts, WBCs, RBCs, and proteinuria
  • Peripheral eosinophilia

Postrenal

UA:

• Usually normal
• May have some hematuria but no casts or protein
• FE_NA often > 4%
• Urine osmolality usually < 350 mmol/kg

Imaging

• US:
  • 98% sensitive for excluding obstruction
• Helical CT scan:
  • Without contrast sensitive for obstruction
  • May detect intrarenal changes
• Duplex scan for:
  • Renal artery or vein thrombosis
• Renal arteriogram:
  • Definitive diagnosis of renal artery thrombosis
• Inferior vena cava and renal vessel venogram for renal vein thrombosis
• IV pyelogram

Diagnostic Procedures/Surgery

ECG:

• Hypertension secondary to volume overload may cause ischemia.
• Sensitive for significant, acute electrolyte changes

[Outline]

• SIGNS AND SYMPTOMS
• ESSENTIAL WORKUP
• DIAGNOSIS TESTS & INTERPRETATION

PRE-HOSPITAL

• Airway, breathing, and circulation (ABCs):
  • Supplemental oxygen for hypoxia
• IV NS for volume depletion

INITIAL STABILIZATION/THERAPY

• ABCs:
• Supplemental oxygen for hypoxia
• IV NS for volume depletion
• Correct electrolyte disturbances
• Indications for emergent dialysis:
  • Intractable hypertension
  • Intractable volume overload
  • Uremic encephalopathy, bleeding, or pericarditis
  • BUN > 100 mg/dL
  • Intractable metabolic acidosis (pH < 7.2)
• Avoid nephrotoxic drugs.
• Monitor UO.

ED TREATMENT/PROCEDURES

Prerenal AKI

• Treat hypoperfusion with IV NS
• Packed RBC for blood loss or anemia after lack of response after 2 boluses
• Invasive cardiac monitoring if unable to assess cardiac failure vs. hypovolemia
• Response to NS good indicator of the degree to which hypovolemia is a factor

ALERT

Intrarenal AKI

• Glomerulonephritis:
  • Glucocorticoids or plasma exchange
• ATN:
  • Volume replacement
• Hyponatremia: Free water restriction
• Hyperkalemia:
  • Sodium polystyrene sulfonate (SPS) or calcium polystyrene sulfonate (CPS) for asymptomatic patient with K⁺ > 5.5 mEq/L
  • For K⁺ > 6.5 mEq/L or ECG abnormalities consistent with hyperkalemia:
    • Albuterol via nebulizer
    • Dextrose and insulin
    • Furosemide if patient not anuric
    • Calcium stabilizes myocardium in severe hyperkalemia
    • Calcium gluconate for awake patient
    • Calcium chloride for patient without pulse
    • Dialysis for intractable hyperkalemia
• Metabolic acidosis:
  • Consider sodium bicarbonate for pH < 7.2 or HCO₃ < 15 mEq/L in chronic disease
  • Hyperphosphatemia:
    • Calcium carbonate
    • Aluminum hydroxide
  • Myoglobinuria—aggressive fluid resuscitation with NS

ALERT

MEDICATION

• Albuterol: 10–20 mg via nebulizer
• Aluminum hydroxide (amphojel): 0.5–1.5 g PO
• Calcium carbonate (Os-Cal): 0.250–3 g PO
• Calcium gluconate: 10 mL of 10% solution over 5 min IV (may repeat q5min)
• Calcium chloride: 10 mL of 10% solution
• Dextrose: D₅₀W 1 amp (50 mL or 25 g) (peds: D₂₅W 2 mL/kg) IV
• Furosemide: 20–400 mg IV push
• Insulin: 0.1 U/kg regular IV with dextrose (decrease dose by 50% for severe renal and/or liver disease)
• Sodium bicarbonate: 1–2 mEq/kg IV
• SPS (Kayexalate) or CPS: 1 g/kg up to 15–60 g PO or 30–50 g retention enema in sorbitol q6h

ALERT

[Outline]

• PRE-HOSPITAL
• INITIAL STABILIZATION/THERAPY
• ED TREATMENT/PROCEDURES
• MEDICATION

DISPOSITION

Admission Criteria

• New-onset AKI
• Hyperkalemia/significant electrolyte abnormalities
• Fluid overload with hypoxia/congestive heart failure
• Uremia
• Altered mental status

Discharge Criteria

• Stable
• Normal electrolytes

Issues for Referral

Refer to primary physician for progressive AKI in an otherwise stable patient.

• Insulin dose for hyperkalemia should be reduced for significant liver or renal disease so as to avoid hypoglycemia.
• NSAIDs to be avoided with any degree of AKI
• SPS has a considerable sodium load; CPS is preferred when volume overload is a concern.
• Avoid contrast if possible in AKI, as it may worsen renal function.

ICD9

• 584.5 Acute kidney failure with lesion of tubular necrosis
• 584.9 Acute kidney failure, unspecified
• 997.5 Urinary complications, not elsewhere classified

ICD10

• N17.0 Acute kidney failure with tubular necrosis
• N17.9 Acute kidney failure, unspecified
• N99.0 Postprocedural (acute) (chronic) kidney failure

[Outline]

• ICD9
• ICD10

• Andreoli S. Acute kidney injury in children. Pediatr Nephrol. 2009;24:253–263.
• Kellum JA. Acute kidney injury. Crit Care Med. 2008;36(suppl):S141–S145.
• Rahman M, Shad F, Smith MC. Acute kidney injury: A guide to diagnosis and management. Amer Fam Physician. 2012;86(7):631–639.

See Also (Topic, Algorithm, Electronic Media Element)

• Hyperkalemia
• Renal Injury

Michael D. Burg

Matthew N. Graber