Rosen & Barkin's 5-Minute Emergency Medicine Consult (606 page)

• 592.0 Calculus of kidney
  
• 592.1 Calculus of ureter
  
• 788.0 Renal colic
  

BASICS

• The disorder is now known as acute kidney injury (AKI); the term renal failure is outdated.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:
    
    • R
      isk: Increased creatinine (Cr) ×1.5 or GFR decrease >25%, UO <0.5 mL/kg/h × >6 h
      
    • I
      njury: Increased Cr ×2 or GFR decrease >50%, UO <0.5 mL/kg/h × >12 h
      
    • F
      ailure: 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:
    
    • L
      oss: Loss of renal function >4 wk
      
    • E
      SRD: 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.
  

• 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)
    

DIAGNOSIS

• 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
  

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

• 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
    

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

• 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
    

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

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

• 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
  

• Prerenal AKI a concern in neonates
  
• Anatomic abnormalities
  

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

• Electrolytes including Ca, Mg, PO
  ₄
  
• 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
  

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
    ⁺
    , PO
    ₄
    , myoglobin, creatine phosphokinase, uric acid
    
  • Decreased serum Ca
    ²⁺
    
• 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
  

• 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
  

ECG:

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

TREATMENT

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

• 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.