DIP Episode 141 - USMLE Step 2CK Rapid Review Series 13 (IM)

Source / episode info

• Episode: 141
• Title: Divine Intervention Episode 141 – USMLE Step 2 CK Rapid Review Series 13 (IM)
• Published: 2019-08-23
• Source: Episode page

One-liner

This episode provides rapid review of high-yield internal medicine topics including acute cholecystitis workup variations, differentiating pleural effusion types using Light's criteria, managing various infectious diarrheas (e.g., Vibrio cholerae, Giardia), understanding coagulation testing principles, and recognizing the pathophysiology of ARDS.

High-yield summary

• Acute Cholecystitis Workup: If RUQ ultrasound is equivocal or negative, proceed with a HIDA scan. A positive test for acute cholecystitis is failure to visualize the gallbladder at 90 minutes post-morphine administration.
• Ecalculous Cholecystitis Management: In high-risk patients (e.g., on TPN, in ICU), do NOT perform an elective cholecystectomy; instead, utilize a percutaneous cholecystostomy to decompress the gallbladder.
• Pleural Effusion Classification: An effusion is exudative if any of the following Light's criteria are met: 1) Pleural fluid/serum protein ratio > 0.5, 2) Pleural fluid/serum LDH ratio > 0.6, or 3) Pleural fluid LDH > 2/3 ULN.
• ARDS Pathophysiology: Non-cardiogenic pulmonary edema (ARDS) is characterized by increased permeability of the pulmonary vasculature and is diagnosed when the Pulmonary Capillary Wedge Pressure (PCWP) is low (< 18 mm Hg), despite severe hypoxemia.
• Coagulation Testing Traps: Warfarin inhibits Vitamin K, leading to decreased synthesis of Factors II, VII, IX, and X. Therefore, it elevates both PT and aPTT. Heparin primarily prolongs the aPTT.

Learning objectives

• Differentiate the diagnostic workup for acute cholecystitis using ultrasound vs. HIDA scan.
• Apply Light's criteria accurately to classify pleural effusions as transudative or exudative.
• Recognize the specific pathogens and clinical presentations associated with various diarrheal syndromes (e.g., Giardia, Vibrio cholerae).
• Understand the pathophysiology of ARDS, particularly differentiating it from cardiogenic pulmonary edema using PCWP.
• Master the principles of coagulation testing interpretation, especially concerning anticoagulants like Warfarin and Heparin.

Board exam buzzwords

Rapid review table

Board-speak -> diagnosis

Differential diagnosis / distinguishing features

Pleural Effusions

Diarrhea Etiologies

Management pearls

• For suspected acute cholecystitis in high-risk patients (ICU/TPN), perform a percutaneous cholecystostomy rather than an elective laparoscopic cholecystectomy due to increased morbidity and mortality risk.
• In the setting of nephrotic syndrome or cirrhosis causing hypoalbuminemia, assume any pleural effusion is likely transudative unless proven otherwise by Light's criteria.
• When managing ARDS, always employ lung protective strategies: low tidal volumes (6 mL/kg) and appropriate PEEP titration.
• For suspected colocolitis due to an obstructing stone in the cystic duct, ERCP is both diagnostic and therapeutic.

Don't miss

Integration & clinical reasoning

• Nephrotic Syndrome & Pleural Effusion: Nephrotic syndrome causes hypoalbuminemia (low oncotic pressure), leading to transudative effusions, which is a key differential diagnosis when evaluating pleural fluid.
• GI Bleeding/Coagulopathy: Severe GI bleeding (e.g., from varices or severe colitis) can lead to consumption of clotting factors and platelets, resulting in DIC (elevated PT and aPTT).
• Drug Overdose Management: The reversal agents for anticholinergic overdose (Atropine) is Physostigmine; the reversal agent for benzodiazepine/Z-drug overdose is also Flumazenil or Pyridostigmine.

OMM / COMLEX integration

• Acute Abdominal Pain: In any patient presenting with acute abdominal pain and signs of peritonitis (e.g., suspected diverticulitis or appendicitis), standard emergency management takes priority over OMT. Surgical consultation is paramount for definitive diagnosis/treatment.
• ARDS Management: Standard critical care protocols (mechanical ventilation, fluid resuscitation) take precedence. OMT should be used adjunctively only after stabilization and in consultation with the primary care team.

Concept connections / cross-references

• For detailed review of GI bleeding and varices, see Episode 105.
• For comprehensive coverage of infectious diarrhea pathogens, see Episode 28.
• For general principles of fluid balance and renal physiology, see Episode 37.

High-yield association table

Key terms glossary

Study optimization

Question pattern recognition

• The "Best Next Step" Question: Requires synthesizing multiple findings (labs, imaging, physical exam) to choose the most appropriate diagnostic or therapeutic action.
• Differential Diagnosis by Location/Symptom: Questions often present a constellation of symptoms (e.g., diarrhea + bloody stool + AKI) requiring selection from several possible diagnoses.
• Physiology Trap Question: Testing knowledge of subtle physiological differences, such as differentiating the cause of pulmonary edema based on PCWP readings.

Test yourself

Common mistakes to avoid

Common traps