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🫁 High-Yield Pulmonary Medicine - Must Know

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1. ASTHMA

Key Facts

• Most common chronic lung disease worldwide (~340 million people); ~8% of US adults affected
• Boys > girls before puberty; women > men after puberty (ratio 1.8:1)
• ~60% heritability (twin studies); genes related to immune mechanisms
• Definition: Recurrent episodes of largely reversible airway obstruction, airway hyperresponsiveness, and airway inflammation

Pathology (Endotypes)

Spirometry in Asthma

• Obstructive pattern: FEV1/FVC < 0.70
• Reversibility: FEV1 increase ≥12% AND ≥200 mL after bronchodilator
• Bronchial provocation test (methacholine): Used when spirometry is normal but asthma is suspected

Severity Classification (GINA)

• Intermittent → Mild persistent → Moderate persistent → Severe persistent
• Based on daytime symptoms, nocturnal awakenings, SABA use, activity limitation, FEV1

Treatment Stepwise (GINA)

1. Step 1: PRN low-dose ICS-formoterol (preferred) or SABA alone
2. Step 2: Low-dose ICS + SABA PRN
3. Step 3: Low-dose ICS-LABA
4. Step 4: Medium-dose ICS-LABA
5. Step 5: High-dose ICS-LABA + add-on therapy (tiotropium, biologics)

Biologic Targets (Severe/Refractory Asthma)

Status Asthmaticus - High-Yield Management

• O2 to keep SpO2 > 92%
• SABA nebulization (salbutamol) every 20 min x3, then continuous
• Ipratropium bromide (add to SABA in severe)
• Systemic corticosteroids (IV methylprednisolone or oral prednisolone)
• IV magnesium sulfate (2g over 20 min) - smooth muscle relaxation
• Heliox (helium-oxygen 70:30) in refractory cases
• Intubation if GCS declining, exhaustion, silent chest

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2. COPD

Key Facts

• FEV1/FVC < 0.70 post-bronchodilator (fixed ratio)
• Smoking is the #1 risk factor (15-20% of smokers develop COPD)
• Alpha-1 antitrypsin deficiency: panacinar emphysema, young patients, lower lobes
• GOLD Staging by FEV1 (% predicted): GOLD 1 ≥80%, GOLD 2 50-79%, GOLD 3 30-49%, GOLD 4 <30%

Emphysema Types

COPD vs. Asthma - Key Distinguishing Features

Pulmonary Hypertension in COPD

• COPD is the most common lung disease associated with PH (>80% of all CLD-PH)
• Most common PH definition: mPAP > 25 mmHg; newer threshold >20 mmHg
• Severe PH (mPAP ≥40 mmHg) is rare in COPD - look for alternate cause
• Low DLCO and arterial PO2/PCO2 predict severe PH - Murray & Nadel's, p. 85

COPD Exacerbation Management

• Controlled O2 (target SpO2 88-92%)
• SABA + SAMA (salbutamol + ipratropium)
• Oral prednisolone 40mg x5 days
• Antibiotics if: increased sputum purulence, increased dyspnea, increased sputum volume (Anthonisen criteria)
• Non-invasive positive pressure ventilation (NIV/BiPAP): PaCO2 >45 with pH <7.35
• Intubate if NIV fails or contraindicated

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3. PULMONARY EMBOLISM (PE)

Wells Score (Pretest Probability)

• Score ≤4: PE "unlikely" → D-dimer; if D-dimer <500 ng/mL: PE excluded
• Score >4: PE "likely" → proceed directly to CTPA

Massive PE

• Hemodynamic instability (shock, systolic BP <90 for ≥15 min)
• Treatment: Systemic thrombolysis (tPA alteplase 100mg over 2h) - first line
• Surgical embolectomy or catheter-directed therapy if thrombolysis contraindicated

Submassive PE

• RV strain on echo/CT but hemodynamically stable
• Anticoagulate; consider thrombolysis if deteriorating

PE in Pregnancy

• LMWH is first-line anticoagulation (warfarin and DOACs are contraindicated)
• D-dimer is less reliable in pregnancy (elevated at baseline)
• V/Q scan preferred over CTPA when possible (less radiation to breast tissue)

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4. INTERSTITIAL LUNG DISEASES (ILD)

ILD Pattern Recognition on HRCT

IPF (Idiopathic Pulmonary Fibrosis)

• UIP pattern on HRCT is diagnostic (in right clinical context; may avoid surgical biopsy)
• Treatment: Pirfenidone or Nintedanib (antifibrotic, slow progression - proven 2014)
• Immunosuppression (steroids) was previously used - now shown to increase morbidity/mortality
• Median survival 3-5 years from diagnosis; lung transplant is definitive therapy
• Harrison's 22E, p. 2306: antifibrotic therapy may also benefit other forms of progressive pulmonary fibrosis

NSIP

• Most common ILD pattern in connective tissue diseases (especially SSc, PM/DM)
• Better prognosis than IPF
• Responds to corticosteroids

Sarcoidosis

Scadding Radiographic Stages

Lofgren Syndrome (Acute Sarcoidosis)

• Triad: BHL + erythema nodosum + arthritis/arthralgia (usually periarthritis of ankles)
• Excellent prognosis; often resolves spontaneously
• Uveitis in sarcoidosis → look for hypercalcemia (activated macrophages produce 1,25-OH vitamin D)

Sarcoidosis-associated PH

• Occurs in advanced (Stage IV) sarcoidosis
• Mechanism: fibrotic compression of vessels, granulomatous vasculitis
• Poor prognosis; consider lung transplant

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5. PLEURAL DISEASE

Transudates vs. Exudates - Light's Criteria

• Pleural/serum protein ratio > 0.5
• Pleural/serum LDH ratio > 0.6
• Pleural LDH > 2/3 upper limit of normal serum LDH

TB Pleuritis

• Exudative effusion, lymphocytic predominance
• Low glucose, high LDH
• High adenosine deaminase (ADA) - most useful test (>40 U/L is suggestive)
• Pleural biopsy: granulomas (higher yield than fluid culture for AFB)

Empyema

• pH < 7.2, glucose <60, positive culture or Gram stain → chest tube drainage mandatory
• If multiple loculations → fibrinolytic agents (tPA + DNase) intrapleural

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6. PNEUMOTHORAX

Classification

Management

• Small primary (<2 cm on CXR): observation + O2 (accelerates absorption)
• Moderate-large (>2 cm) or symptomatic: aspiration or chest tube
• Tension PTX: immediate needle decompression (2nd ICS, midclavicular line) → then chest tube
• Recurrent: chemical pleurodesis or VATS with bullectomy

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7. TUBERCULOSIS

Key Diagnostic Tests

Active TB Treatment

Drug Side Effects (Critical!)

LTBI (Latent TB) Treatment

• INH x9 months (standard) or INH + rifapentine x3 months (3HP regimen)
• Screen before starting anti-TNF therapy (biologics)

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8. PNEUMONIA

Classification and Organisms

Atypical Pneumonia Clues

• Mycoplasma: Young adults, "walking pneumonia," cold agglutinins, bullous myringitis
• Legionella: Water towers, hotel/hospital outbreaks; hyponatremia, diarrhea, mental confusion; urine antigen test (best rapid test); treat with fluoroquinolone or azithromycin
• Chlamydophila psittaci: Bird exposure (parrots, psittacines)

CURB-65 Score (Severity/Admission)

• Score 0-1: Outpatient; Score 2: Short admission; Score 3-5: ICU consideration

PCP (Pneumocystis jirovecii Pneumonia)

• HIV patients with CD4 <200
• Dry cough, dyspnea on exertion, fever; CXR: bilateral ground-glass perihilar infiltrates
• Elevated LDH; diagnosis by BAL (silver stain, immunofluorescence)
• Treatment: TMP-SMX (high dose); add prednisone if PaO2 <70 mmHg
• Prophylaxis: TMP-SMX when CD4 <200

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9. LUNG CANCER

Types and Key Features

Paraneoplastic Syndromes

Pancoast Tumor (Superior Sulcus Tumor)

• Apex of lung invading T1 nerve root, brachial plexus, subclavian vessels, sympathetic chain
• Horner's syndrome: Ptosis + miosis + anhidrosis
• Shoulder/arm pain radiating to ulnar distribution (C8-T2)
• Treatment: Concurrent chemoradiation → surgery

SCLC Treatment

• Extremely chemosensitive; Etoposide + Cisplatin (EP regimen) standard first line
• Prophylactic cranial irradiation (PCI) for limited and extensive stage responders (reduces brain mets)
• Limited stage: chemoradiation
• Extensive stage: chemotherapy ± immunotherapy (atezolizumab/durvalumab)

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10. PULMONARY FUNCTION TESTS (PFTs) - The Foundation

Obstructive vs. Restrictive

Flow-Volume Loop Patterns

• Obstructive: Scooped-out expiratory curve, hyperinflation
• Fixed upper airway obstruction: Plateau on both inspiration AND expiration
• Variable extrathoracic obstruction: Plateau on inspiration only (eg vocal cord paralysis)
• Variable intrathoracic obstruction: Plateau on expiration only

DLCO Patterns

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11. ARTERIAL BLOOD GAS (ABG) INTERPRETATION

Step-by-Step Approach

1. pH: acidosis (<7.35) or alkalosis (>7.45)
2. Primary disorder: pCO2 (respiratory) vs. HCO3 (metabolic)
3. Compensation (is it appropriate?)
4. Anion gap if metabolic acidosis

Compensation Formulas

A-a Gradient

• Formula: PAO2 - PaO2 = [(FiO2 × 713) - (PaCO2/0.8)] - PaO2
• Normal: age/4 + 4 (increases with age)
• Elevated A-a with low PaO2: V/Q mismatch, diffusion limitation, intracardiac/intrapulmonary shunt
• Normal A-a with low PaO2: Hypoventilation, high altitude

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12. SLEEP APNEA

OSA vs. Central Sleep Apnea

OSA

• Apnea-Hypopnea Index (AHI): Mild 5-14, Moderate 15-29, Severe ≥30
• STOP-BANG screening tool (≥3 is high-risk)
• CPAP: first-line treatment
• Complications: hypertension, AFib, pulmonary hypertension, metabolic syndrome

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13. CYSTIC FIBROSIS

• CFTR gene mutation (chromosome 7q); most common: ΔF508 (Phe508del)
• Thick, tenacious secretions; obstructive pattern on PFTs
• Classic bugs: Pseudomonas aeruginosa (most common after childhood), Staphylococcus aureus, Burkholderia cepacia (worst prognosis)
• Diagnosis: Sweat chloride >60 mEq/L (two tests)
• CFTR modulators: Elexacaftor/tezacaftor/ivacaftor (Trikafta) - game-changing for ΔF508
• Complications: bronchiectasis, pneumothorax, cor pulmonale, male infertility (absent vas deferens), fat-soluble vitamin deficiency, diabetes

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14. QUICK HIGH-YIELD MNEMONICS

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EXAM TRAPS TO AVOID

1. Fixed ratio FEV1/FVC <0.70 = COPD (not Z-score; post-bronchodilator)
2. IPF: steroids worsen outcomes - give antifibrotics (pirfenidone/nintedanib)
3. Massive PE = hemodynamic instability → systemic thrombolysis (not just anticoagulation)
4. Legionella: Urine antigen (best rapid test); treat with fluoroquinolone, NOT beta-lactam
5. D-dimer is a rule-OUT, not rule-IN test (high sensitivity, low specificity)
6. Tension PTX: don't wait for CXR → immediate needle decompression
7. TB + HIV: Start ART 2-8 weeks after starting TB treatment (not simultaneously - IRIS risk); EXCEPT if CD4 <50 → start ART within 2 weeks
8. SCLC is treated with chemo/radiation, NOT surgery (almost never resectable)
9. Methotrexate, amiodarone, bleomycin, nitrofurantoin - drug-induced ILD (exam favorites)
10. Spontaneous pneumothorax in a young man + Marfan features → suspect Marfan's

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