Key Clinical Formulas & Scores
C = Confusion (new onset) (1)
U = Urea (BUN) >19 mg/dL (7 mmol/L) (1)
R = Respiratory rate β₯30/min (1)
B = Blood pressure: SBP <90 or DBP β€60 (1)
65 = Age β₯65 years (1)
Score: 0-1 = outpatient, 2 = admit, 3-5 = ICU consideration
Mortality: 0=0.7%, 1=3.2%, 2=13%, 3=17%, 4=41.5%, 5=57%
Clinical signs of DVT (3 pts)
PE most likely diagnosis (3 pts)
Heart rate >100 bpm (1.5 pts)
Immobilization/surgery in past 4 weeks (1.5 pts)
Previous DVT/PE (1.5 pts)
Hemoptysis (1 pt)
Malignancy (1 pt)
Score β€4 = PE unlikely (D-dimer if negative β exclude)
Score >4 = PE likely (CTPA directly)
ARDS: P/F β€300 with bilateral infiltrates, not fully explained by cardiac failure
Mild ARDS: 200 < P/F β€ 300 (with PEEP β₯5 cmHβO)
Moderate ARDS: 100 < P/F β€ 200
Severe ARDS: P/F β€ 100
A-a gradient = PAOβ - PaOβ (normal <10-15 mmHg on room air)
PAOβ = FiOβ(PB - PHβO) - (PaCOβ/0.8) = 0.21(760-47) - (PaCOβ/0.8)
B = BMI (β€21=1 point)
O = Obstruction (FEVβ % predicted: β₯65%=0, 50-64%=1, 36-49%=2, β€35%=3)
D = Dyspnea (mMRC scale 0-4: 0-1=0, 2=1, 3=2, 4=3)
E = Exercise capacity (6MWD: β₯350m=0, 250-349=1, 150-249=2, β€149=3)
Score 0-2: 4-year mortality ~16% | Score 4-6: ~38% | Score 7-10: ~80%
Post-bronchodilator FEVβ/FVC <0.70 confirms airflow limitation
GOLD 1 (Mild): FEVβ β₯80% predicted
GOLD 2 (Moderate): 50-79% predicted
GOLD 3 (Severe): 30-49% predicted
GOLD 4 (Very Severe): <30% predicted
Symptoms: CAT score or mMRC
Exacerbations: ABE assessment β Group A (few symptoms, 0-1 moderate exacerbations): bronchodilator; Group B (more symptoms): LABA+LAMA; Group E (β₯2 moderate or β₯1 hospitalization): LABA+LAMA Β± ICS
Core Concepts
Asthma (GINA Guidelines)
Chronic airway inflammation with reversible airflow obstruction and bronchial hyperresponsiveness. Classification: intermittent, mild persistent, moderate persistent, severe persistent. Stepwise approach (GINA 2024): Step 1: as-needed low-dose ICS-formoterol. Step 2: daily low-dose ICS + as-needed SABA, or as-needed ICS-formoterol. Step 3: low-dose ICS-LABA. Step 4: medium-dose ICS-LABA. Step 5: high-dose ICS-LABA + LAMA Β± biologics (anti-IgE, anti-IL-5, anti-IL-4RΞ±). Exacerbation management: Oβ, nebulized SABA + ipratropium, systemic corticosteroids (prednisolone 40-50 mg Γ 5-7 days), IV magnesium sulfate for severe.
COPD & Oxygen Therapy
Chronic bronchitis (productive cough β₯3 months/year Γ 2 years) and/or emphysema (destruction of alveoli, air trapping). Smoking is primary cause (85-90%). Treatment: smoking cessation (most effective), bronchodilators (SABA, LABA, LAMA), ICS for frequent exacerbations with eosinophils β₯300, pulmonary rehabilitation, oxygen (PaOβ β€55 or SaOβ β€88%), lung volume reduction surgery or transplant for severe. Exacerbation: bronchodilators, corticosteroids, antibiotics if purulent sputum, NIV for acute respiratory failure (pH β€7.35 with hypercapnia).
Pulmonary Embolism (PE)
Virchow's triad: stasis, hypercoagulability, endothelial injury. Clinical: dyspnea (most common), pleuritic chest pain, cough, hemoptysis, syncope (massive PE). Massive PE: hypotension, cardiogenic shock. Submassive: RV dysfunction (echo: RV dilation, elevated troponin, BNP) without hypotension. Diagnosis: CTPA (gold standard), V/Q scan if contraindication to contrast. Treatment: anticoagulation (LMWH β DOAC or warfarin) for β₯3 months. Systemic thrombolysis (alteplase 100 mg Γ 2 hrs) for massive PE. Catheter-directed therapy or surgical embolectomy if contraindications to thrombolysis. IVC filter if anticoagulation contraindicated.
Clinical Case Studies
Case 1: Community-Acquired Pneumonia
Patient: 58-year-old male, fever 39.2Β°C, productive cough with rusty sputum, pleuritic chest pain Γ 3 days. RR 28, HR 105, BP 105/70. Crackles in right lower lobe. Labs: WBC 18,000, BUN 22, creatinine 1.1. CXR: right lower lobe consolidation with air bronchograms.
Assessment: CURB-65 = 2 (BUN >19 + RR β₯30 would be 3, but RR is 28 β only BUN and confusion absent β actually: BUN 22>19=1, no confusion=0, RR 28<30=0, BP normal=0, age 58<65=0 β Score 1). Pneumonia Severity Index (PSI) Class III β admit.
Management: Ceftriaxone 1g IV q24h + azithromycin 500mg IV q24h Γ 5 days. Oβ to keep SpOβ β₯92%. IV fluids. Follow-up CXR at 6 weeks if age >50 or smoker. Risk factors: smoking, age >65, comorbidities.
Case 2: Acute Pulmonary Embolism
Patient: 45-year-old female, sudden dyspnea and pleuritic chest pain Γ 6 hours. HR 118, RR 28, SpOβ 91% on room air. PMH: obesity (BMI 38), oral contraceptive use, recent long-haul flight. Wells score = 7.5 (signs of DVT 3 + PE likely 3 + HR>100 1.5). CTPA: large filling defect in right main pulmonary artery extending into lobar branches. Echo: RV dilation, elevated troponin 0.8.
Diagnosis: Submassive (intermediate-high risk) PE β RV dysfunction + positive biomarkers without hypotension.
Management: Therapeutic anticoagulation: enoxaparin 1 mg/kg SC q12h or rivaroxaban 15 mg BID Γ 21 days then 20 mg daily. Oβ therapy. Hemodynamic monitoring. No systemic thrombolysis (not massive PE). If clinical deterioration β rescue thrombolysis. Discharge when stable on DOAC (if no RV dysfunction, can discharge early). Minimum 3 months anticoagulation; indefinite if unprovoked or recurrent.
Case 3: COPD Exacerbation with Respiratory Failure
Patient: 72-year-old male, COPD (GOLD 3, FEVβ 42%), presents with increased dyspnea, purulent sputum Γ 5 days. ABG on 2L NC: pH 7.28, PaCOβ 68, PaOβ 52, HCOβ 32. SpOβ 88%. Bilateral wheezes, prolonged expiratory phase.
Diagnosis: Acute exacerbation of COPD (AECOPD) with acute on chronic respiratory acidosis (pH <7.35 + PaCOβ >45 = NIV indicated).
Management: NIV (BiPAP: IPAP 10-15, EPAP 4-5) β reduces intubation and mortality. Nebulized salbutamol + ipratropium q1h. IV methylprednisolone 40mg daily Γ 5 days. Antibiotics: azithromycin 500mg daily Γ 5 days (purulent sputum). Controlled oxygen therapy (Venturi mask 24-28%, target SpOβ 88-92%). Avoid high-flow Oβ (risk of COβ narcosis). If NIV fails or pH <7.25 β intubation and mechanical ventilation.
Practice Questions
A: Score = 4 (confusion 1 + RRβ₯30 1 + BP<90/60 1 + ageβ₯65 1). High risk β admit to ICU. Mortality ~41%.
A: P/F = 65/0.5 = 130. Moderate ARDS (100 < P/F β€ 200).
A: NIV reduces work of breathing, improves alveolar ventilation (washes out COβ), recruits collapsed alveoli, and unloads respiratory muscles. Indicated when pH β€7.35 with hypercapnia despite optimal medical therapy.
A: Wells score >4 = PE likely β proceed directly to CT pulmonary angiography (CTPA). No D-dimer needed.
A: 88-92%. Higher FiOβ can suppress hypoxic drive, worsen V/Q mismatch, and cause COβ narcosis. Use controlled oxygen therapy (Venturi mask or 2L NC) and monitor ABG.