Key Clinical Formulas
MELD Score (Liver Disease):
MELD = 3.78×ln[bilirubin] + 11.2×ln[INR] + 9.57×ln[creatinine] + 6.43
≥15: liver transplant evaluation; ≥40: 50-70% 3-month mortality
MELD = 3.78×ln[bilirubin] + 11.2×ln[INR] + 9.57×ln[creatinine] + 6.43
≥15: liver transplant evaluation; ≥40: 50-70% 3-month mortality
Rockall Score (GI Bleed):
Age + shock + comorbidities + diagnosis + stigmata
≥8: high risk of rebleeding/death; <3: low risk, discharge possible
Age + shock + comorbidities + diagnosis + stigmata
≥8: high risk of rebleeding/death; <3: low risk, discharge possible
Core Concepts
1. GERD and Esophageal Disorders
Gastroesophageal reflux disease: heartburn, regurgitation, erosive esophagitis. Complications: Barrett's esophagus (intestinal metaplasia → adenocarcinoma risk 30-60×). Treatment: PPIs (omeprazole), lifestyle, fundoplication for refractory cases.
Gastroesophageal reflux disease: heartburn, regurgitation, erosive esophagitis. Complications: Barrett's esophagus (intestinal metaplasia → adenocarcinoma risk 30-60×). Treatment: PPIs (omeprazole), lifestyle, fundoplication for refractory cases.
2. Inflammatory Bowel Disease (IBD)
Crohn's disease: transmural inflammation, skip lesions, any GI segment. Ulcerative colitis: mucosal inflammation, continuous, colon only. Both have extraintestinal manifestations. Treatment: 5-ASA, steroids, immunomodulators, biologics (anti-TNF, anti-integrin, anti-IL12/23).
Crohn's disease: transmural inflammation, skip lesions, any GI segment. Ulcerative colitis: mucosal inflammation, continuous, colon only. Both have extraintestinal manifestations. Treatment: 5-ASA, steroids, immunomodulators, biologics (anti-TNF, anti-integrin, anti-IL12/23).
3. Liver Disease
Hepatitis (viral A/B/C, alcoholic, autoimmune). Cirrhosis: portal hypertension → varices, ascites, encephalopathy, hepatocellular carcinoma. NAFLD/NASH now leading cause — obesity/diabetes epidemic.
Hepatitis (viral A/B/C, alcoholic, autoimmune). Cirrhosis: portal hypertension → varices, ascites, encephalopathy, hepatocellular carcinoma. NAFLD/NASH now leading cause — obesity/diabetes epidemic.
4. GI Bleeding
Upper GI: peptic ulcers (H. pylori, NSAIDs), varices, Mallory-Weiss. Lower GI: diverticulosis, angiodysplasia, IBD, malignancy. Management: hemodynamic stabilization, endoscopy within 24 hours, PPIs for ulcers.
Upper GI: peptic ulcers (H. pylori, NSAIDs), varices, Mallory-Weiss. Lower GI: diverticulosis, angiodysplasia, IBD, malignancy. Management: hemodynamic stabilization, endoscopy within 24 hours, PPIs for ulcers.
5. Pancreatic Disease
Acute pancreatitis: gallstones (#1), alcohol (#2), severe epigastric pain radiating to back, elevated lipase >3×. Chronic pancreatitis: irreversible destruction, malabsorption, diabetes, chronic pain. Pancreatic cancer: poor prognosis, Whipple procedure.
Acute pancreatitis: gallstones (#1), alcohol (#2), severe epigastric pain radiating to back, elevated lipase >3×. Chronic pancreatitis: irreversible destruction, malabsorption, diabetes, chronic pain. Pancreatic cancer: poor prognosis, Whipple procedure.
Core Definitions
Barrett's Esophagus: Intestinal metaplasia of the distal esophagus (goblet cells replacing squamous epithelium). Premalignant for adenocarcinoma. Surveillance endoscopy every 3-5 years if no dysplasia; more frequent with dysplasia. Ablation therapy for dysplasia.
Dysphagia: Difficulty swallowing. Mechanical obstruction (stricture, tumor, eosinophilic esophagitis). Motility disorders (achalasia, diffuse spasm). Evaluation: barium swallow, endoscopy, manometry.
Hepatic Encephalopathy: Neuropsychiatric impairment from liver failure. Ammonia crosses blood-brain barrier → astrocyte swelling. Precipitants: GI bleeding, infection, constipation, medications. Treatment: lactulose (traps ammonia), rifaximin (reduces ammonia-producing bacteria).
Worked Examples
Example 1: MELD Score
Bilirubin 3.0, INR 1.5, creatinine 1.2:
MELD = 3.78×ln(3.0) + 11.2×ln(1.5) + 9.57×ln(1.2) + 6.43
= 3.78×1.10 + 11.2×0.41 + 9.57×0.18 + 6.43
= 4.16 + 4.59 + 1.72 + 6.43 = 16.9 → MELD 17 (transplant evaluation threshold met)
Bilirubin 3.0, INR 1.5, creatinine 1.2:
MELD = 3.78×ln(3.0) + 11.2×ln(1.5) + 9.57×ln(1.2) + 6.43
= 3.78×1.10 + 11.2×0.41 + 9.57×0.18 + 6.43
= 4.16 + 4.59 + 1.72 + 6.43 = 16.9 → MELD 17 (transplant evaluation threshold met)
Example 2: Child-Pugh Classification
Bilirubin 2.5 (2 pts), albumin 2.8 (2 pts), INR 1.7 (2 pts), mild ascites (2 pts), no encephalopathy (1 pt)
Total = 9 → Class B (moderate liver dysfunction, 80% 1-year survival)
Bilirubin 2.5 (2 pts), albumin 2.8 (2 pts), INR 1.7 (2 pts), mild ascites (2 pts), no encephalopathy (1 pt)
Total = 9 → Class B (moderate liver dysfunction, 80% 1-year survival)
Example 3: Anion Gap Interpretation
Na=140, Cl=100, HCO₃=15: AG = 140 − (100+15) = 25 (elevated).
High AG acidosis → lactic acidosis, renal failure, toxins. If normal AG → GI losses (diarrhea). delta gap = measured AG − 12 = 13 → also check for concurrent metabolic alkalosis.
Na=140, Cl=100, HCO₃=15: AG = 140 − (100+15) = 25 (elevated).
High AG acidosis → lactic acidosis, renal failure, toxins. If normal AG → GI losses (diarrhea). delta gap = measured AG − 12 = 13 → also check for concurrent metabolic alkalosis.
Practice Problems
Problem 1: Calculate MELD for bilirubin 2.0, INR 1.2, creatinine 1.0.
Answer: MELD = 3.78×ln(2) + 11.2×ln(1.2) + 9.57×ln(1) + 6.43 = 3.78×0.69 + 11.2×0.18 + 0 + 6.43 = 2.61+2.02+6.43 = 11
Answer: MELD = 3.78×ln(2) + 11.2×ln(1.2) + 9.57×ln(1) + 6.43 = 3.78×0.69 + 11.2×0.18 + 0 + 6.43 = 2.61+2.02+6.43 = 11
Problem 2: What are the two main types of inflammatory bowel disease and their key difference?
Answer: Crohn's disease: transmural, skip lesions, any GI segment. Ulcerative colitis: mucosal, continuous, colon only. Crohn's can affect anywhere from mouth to anus.
Answer: Crohn's disease: transmural, skip lesions, any GI segment. Ulcerative colitis: mucosal, continuous, colon only. Crohn's can affect anywhere from mouth to anus.
Problem 3: A cirrhotic patient presents with altered mental status. What is the diagnosis and first-line treatment?
Answer: Hepatic encephalopathy. First-line: lactulose 25 mL every 1-2 hours until 2-3 soft stools/day. Rifaximin 550 mg BID as adjunct. Identify and treat precipitant (infection, GI bleed, constipation).
Answer: Hepatic encephalopathy. First-line: lactulose 25 mL every 1-2 hours until 2-3 soft stools/day. Rifaximin 550 mg BID as adjunct. Identify and treat precipitant (infection, GI bleed, constipation).
Problem 4: What is the most common cause of upper GI bleeding?
Answer: Peptic ulcer disease (gastric/duodenal ulcers). Main risk factors: H. pylori infection and NSAID use. Treatment: PPI infusion, endoscopy with hemostasis (clip, cautery, injection).
Answer: Peptic ulcer disease (gastric/duodenal ulcers). Main risk factors: H. pylori infection and NSAID use. Treatment: PPI infusion, endoscopy with hemostasis (clip, cautery, injection).
Problem 5: Differentiate steatorrhea from other types of diarrhea.
Answer: Steatorrhea: bulky, pale, foul-smelling, oily/floating stools that are difficult to flush. Indicates fat malabsorption (pancreatic insufficiency, bile acid deficiency, celiac disease). Other diarrhea: watery (infectious, osmotic), bloody (IBD, infection).
Answer: Steatorrhea: bulky, pale, foul-smelling, oily/floating stools that are difficult to flush. Indicates fat malabsorption (pancreatic insufficiency, bile acid deficiency, celiac disease). Other diarrhea: watery (infectious, osmotic), bloody (IBD, infection).