Chapter 12 of 159% of exam

Pulmonary System

The pulmonary block covers obstructive and restrictive disease, infections from bronchiolitis to tuberculosis, pulmonary circulation, pleural disease, neoplasms and sleep apnea. Pediatric airway emergencies and adult chronic lung disease sit side by side.

Obstruction, restriction and pleura

Spirometry and pleural fluid criteria are applied as fixed rules. Obstruction lowers the FEV1/FVC ratio, while restriction lowers lung volumes with a preserved ratio. Granulomatous disease is identified on biopsy.

COPD spirometry
Post-bronchodilator FEV1/FVC below 0.70; FEV1 percent predicted grades severity.
GOLD 2026 Report
Light's criteria
Exudate if protein ratio above 0.5, LDH ratio above 0.6, or fluid LDH above two thirds of the serum upper limit.
Merck Manual Professional Edition, Pleural Effusion
Sarcoidosis
Bilateral hilar adenopathy with noncaseating granulomas.
Merck Manual Professional Edition, Sarcoidosis

Emergencies and pulmonary circulation

Clinical probability steers the pulmonary embolism work-up. Tension pneumothorax is treated before imaging. Lung cancer types have characteristic locations and paraneoplastic syndromes.

Pulmonary embolism
Low probability: D-dimer; high probability or positive D-dimer: CT angiography.
Merck Manual Professional Edition, Pulmonary Embolism
Tension pneumothorax
Immediate needle decompression without waiting for a radiograph.
Merck Manual Professional Edition, Pneumothorax
Small cell lung cancer
Central tumor associated with SIADH.
Merck Manual Professional Edition, Lung Carcinoma

Pediatric airway and sleep

Stridor in a child is sorted by onset, fever and drooling. Viral lower-respiratory illness in infants is mostly managed supportively. Sleep apnea and cystic fibrosis each have a specific confirmatory test.

Croup
Barking cough and stridor; dexamethasone, plus racemic epinephrine when moderate to severe; steeple sign.
Merck Manual Professional Edition, Croup
Epiglottitis
Thumb sign, drooling and toxicity; secure the airway.
Merck Manual Professional Edition, Epiglottitis
Bronchiolitis
Supportive care; routine bronchodilators and steroids are not recommended.
AAP Clinical Practice Guideline: Bronchiolitis (2014)
Sleep apnea and CF
Sleep studies confirm OSA; elevated sweat chloride confirms cystic fibrosis.
Merck Manual Professional Edition, Obstructive Sleep Apnea; Cystic Fibrosis

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