Master Advanced Clinical Medicine (ACM)
for USMLE Step 3

Core Concepts

Advanced Clinical Medicine (ACM) for USMLE Step 3 emphasizes the integrated management of complex, acutely ill hospitalized patients across various specialties. It requires rapid assessment, differential diagnosis, evidence-based management of life-threatening conditions, interpretation of multi-system data, and understanding disease progression and complications. Focus on initial stabilization, timely intervention, and anticipating deterioration. Key areas include critical care, perioperative management, acute exacerbations of chronic diseases, and common inpatient medical emergencies.

Clinical Presentation

• Shock Syndromes: Hypotension, tachycardia, altered mental status, poor end-organ perfusion (e.g., cool extremities, oliguria). Differentiate cardiogenic, hypovolemic, septic, obstructive, and distributive shock based on history, physical, and hemodynamics.
• Acute Respiratory Failure: Dyspnea, tachypnea, hypoxemia (PaO2 <60 mmHg), hypercapnia (PaCO2 >45 mmHg with acidosis), increased work of breathing, accessory muscle use. Can be hypoxic (Type I, e.g., ARDS, pneumonia) or hypercapnic (Type II, e.g., COPD exacerbation, opioid overdose).
• Altered Mental Status (AMS): Acute change in attention, awareness, or cognition. Causes include metabolic derangements (hypo/hyperglycemia, uremia, hypercalcemia), infection (sepsis, meningitis), drug toxicity, structural brain lesions, seizures, hypoxia.
• Acute Organ Dysfunction:
  • AKI: Oliguria/anuria, elevated BUN/Cr, electrolyte abnormalities (hyperkalemia, hyponatremia, hyperphosphatemia).
  • Acute Liver Failure: Jaundice, coagulopathy, hepatic encephalopathy, hypoglycemia.
  • GI Bleeding: Hematemesis, melena, hematochezia, signs of hypovolemia.
• Severe Electrolyte Derangements:
  • Hyponatremia: Nausea, headache, confusion, seizures, cerebral edema.
  • Hyperkalemia: Muscle weakness, paresthesias, peaked T waves, widened QRS, bradycardia, asystole.

Diagnosis (Gold Standard)

Diagnosis in ACM often involves rapid bedside assessment followed by confirmatory tests:

• Shock: Initial workup (lactate, ABG, CBC, BMP, cultures, cardiac enzymes), EKG, bedside ultrasound (FAST exam, ECHO for cardiac function/effusion). Gold standard for specific types varies (e.g., Swan-Ganz for cardiogenic).
• Sepsis/Septic Shock: Two sets of blood cultures (before antibiotics), lactate >2 mmol/L, cultures from other suspected sites.
• Acute Respiratory Failure: ABG (PaO2, PaCO2, pH), CXR/CT chest, P/F ratio (for ARDS <300).
• AKI: Serial creatinine, urine output, fractional excretion of sodium (FENa), renal ultrasound.
• Upper GI Bleed: Upper Endoscopy (diagnostic and therapeutic).
• Lower GI Bleed: Colonoscopy (diagnostic and therapeutic), CTA/Angiography for active severe bleeding.
• Severe Hyperkalemia: EKG changes (peaked T waves, widened QRS, absent P waves), serum potassium >6.5 mEq/L.
• Severe Hyponatremia: Serum sodium <120 mEq/L, osmolality (serum and urine).

Management (First Line)

• Sepsis/Septic Shock:
  • Fluid Resuscitation: 30 mL/kg IV crystalloid within 3 hours.
  • Antibiotics: Broad-spectrum IV antibiotics within 1 hour (empiric coverage for likely pathogens).
  • Vasopressors: Norepinephrine first-line if hypotensive despite fluids (MAP target ≥65 mmHg).
  • Source Control: Identify and drain/remove infection source.
• Acute Respiratory Failure:
  • Oxygen: Supplementation (nasal cannula, non-rebreather) to maintain SpO2 >90%.
  • Ventilatory Support: Non-invasive (BiPAP/CPAP) if appropriate, otherwise intubation and mechanical ventilation.
  • ARDS Specific: Low tidal volume ventilation (4-8 mL/kg PBW), PEEP titration, prone positioning.
  • COPD Exacerbation: Bronchodilators (albuterol, ipratropium), systemic corticosteroids, antibiotics if purulent sputum.
• AKI:
  • Prerenal: IV fluid resuscitation (crystalloids), treat underlying cause (e.g., heart failure).
  • Intrinsic: Remove nephrotoxins, treat underlying disease (e.g., vasculitis), avoid contrast, consider steroids for glomerulonephritis.
  • Postrenal: Relieve obstruction (e.g., Foley catheter for BPH, nephrostomy tube).
  • Severe: Dialysis for uremic symptoms, refractory hyperkalemia, fluid overload, severe acidosis.
• Acute GI Bleed (Upper):
  • Resuscitation: IV fluids, blood products (pRBCs for Hgb <7, FFP for coagulopathy, platelets for thrombocytopenia).
  • PPI: High-dose IV proton pump inhibitors.
  • Endoscopy: Early endoscopy with therapeutic intervention (clipping, cautery, epinephrine injection).
  • Variceal Bleed: Octreotide, antibiotics, endoscopic banding/sclerotherapy, consider TIPS.
• Severe Hyperkalemia (with EKG changes or K >6.5):
  • Membrane Stabilization: Calcium gluconate (IV) to protect myocardium.
  • Shift Potassium Intracellularly: Insulin + glucose, beta-agonists (albuterol), sodium bicarbonate.
  • Remove Potassium: Loop diuretics, potassium binders (Kayexalate), hemodialysis.
• Severe Hyponatremia (symptomatic, Na <120):
  • Slow Correction (Chronic): Hypertonic saline (3% NaCl) at a slow rate (e.g., 1-2 mL/kg/hr) to raise Na by 4-6 mEq/L in 24 hours to prevent osmotic demyelination syndrome.
  • Acute Correction (Acute onset, seizures): Rapid initial bolus of 3% NaCl.
  • Underlying Cause: Treat SIADH (fluid restriction, vasopressin receptor antagonists), adrenal insufficiency, etc.