⌘K
Volume 10

A study guide to respirology.

For the internal medicine resident who'd rather read the flow-volume loop than hold their breath through rounds. Designed to keep your pulmonary reasoning well-ventilated and your differentials adequately oxygenated. Last revised 2026.

07 topics

Respirology

Airways · Parenchyma · Pleura · Vasculature · Sleep

01

Asthma

▾
Clinical Picture

Diurnal variation · wheeze · dyspnea · chest tightness · cough — symptoms that wax and wane and worsen overnight.

Establishing the Diagnosis

Demonstrating variable airflow obstruction

TestThreshold for diagnosis
Bronchodilator / 4-wk ICS↑ FEV1 ≥12% + ≥200 mL
PEF variation≥20%
Methacholine challenge↓ FEV1 ≥20% · CI in pregnancy — use when PFTs normal
Exercise challenge↓ FEV1 ≥10% + ≥200 mL
Occupational asthmaSpirometry before + after workplace exposure
  • Non-pharmacologic › allergen/trigger avoidance · allergen immunotherapy · smoking cessation · vaccinations · avoid NSAIDs/β-blockers · treat GERD & obesity
Stepwise Pharmacologic Escalation
Step up when uncontrolled; step down when stable
Daily low-dose ICS + PRN SABA
› medium-dose ICS
› ICS/LABA
› add LAMA or LTRA
› high-dose ICS
› macrolide · biologics (tezepelumab, anti-IgE, anti-IL5, anti-IL4/IL13, anti-TSLP)
Critical Safety Point

LABA monotherapy › ↑ mortality. Never use a LABA without an ICS.

Well-Controlled Asthma

Daytime symptoms ≤2 d/wk · nighttime symptoms ≤1 night/wk · normal activity · mild/infrequent exacerbations · no work/school absence · reliever ≤2 doses/wk · FEV1/PEF ≥90% · PEF variation ≤10–15% · sputum eosinophils <2–3%.

Well-controlled >2 months + low exacerbation risk › step down.

  • Allergic asthma: atopy, nasal polyps, eosinophilia, ↑IgE, ↑FeNO › skin prick & allergen-specific IgE
  • 2nd trimester pregnancy › ↑ exacerbations
Severe Asthma

Requires high-dose ICS + LAMA/LTRA for ≥12 months, or systemic steroids ≥50% of the year.

Investigate for ABPA, bronchiectasis, tracheal/laryngeal obstruction › blood & sputum eosinophils, FeNO, aspergillus-specific IgE/IgG, total IgE, aspergillus antigen skin test, flow-volume loops, laryngoscopy.

Biomarker-Directed Workup & Biologics

Match the phenotype to the target

FindingAction
Eosinophils >1.5Investigate for EGPA
Eosinophils >0.3Investigate for strongyloides
↑ IgEAnti-IgE — omalizumab
Eosinophils >150Anti-IL5 (mepolizumab, reslizumab, benralizumab) · anti-IL4/IL13 (dupilumab)
AERD — Samter's Triad

Asthma + nasal polyps + sinusitis + ASA/NSAID sensitivity › avoid ASA & COX-1 NSAIDs (celecoxib safe) · ICS + LTRA.

Acute Exacerbation

SABA · ipratropium · glucocorticoids 5–7 d › IV MgSO4

  • No response at 4–6 h › hospitalization
  • PEF 60–80% › discharge
  • Normalizing pCO2 in a tiring patient › impending respiratory arrest
02

COPD

▾
Phenotypes & Picture

Driven by smoking. Encompasses emphysema, chronic bronchitis, obliterative bronchiolitis, asthmatic bronchitis. Productive cough · dyspnea · decreased exercise tolerance · fatigue.

  • Diagnosis: post-bronchodilator FEV1/FVC <0.7 › check A1AT (suspect A1AD if age <45 y)

GOLD Severity by FEV1

Post-bronchodilator % predicted

GradeFEV1
Mild≥80%
Moderate50–80%
Severe30–50%
Very severe<30%
  • Asthma/COPD overlap: some bronchodilator reversibility, atopy, ↑IgE, ↑FeNO, eosinophilia
  • ↑ risk recurrent exacerbations: FEV1 <50% · ≥2/y · prior hospitalization for exacerbation
  • Frequent exacerbations › CT chest (bronchiectasis, emphysema, bullae)
  • Non-pharmacologic: smoking cessation · exercise · pulmonary rehab (FEV1 <50%) · vaccinations (influenza, pneumococcal, COVID-19, RSV)
    • Smoking cessation › varenicline, bupropion, NRT
Pharmacologic Escalation
Inhaled foundation → add-on therapy → surgical
PRN SABA (mild)
› LABA and/or LAMA
› LABA/LAMA/ICS (eosinophils >300)
› macrolide · mucolytics · PDE4i roflumilast (bronchitis)
› lung volume reduction surgery (upper-lobe emphysema) · lung transplant
  • Eosinophils ≥300 › dupilumab
  • Lung volume reduction surgery CI: FEV1 <20%, DLCO <20%

Oxygen & Ventilatory Support

Indications by thresholds

TherapyIndication
Supplemental O2arterial pO2 ≤55 · SpO2 ≤88%
LTOTarterial pO2 ≤59 + tissue hypoxia (polycythemia, PH, right-sided HF)
NIV (chronic)severe + PaCO2 ≥52
Acute Exacerbation

Short-acting bronchodilators · prednisone 40 mg PO OD ×5–7 d · ± antibiotics ×5–7 d (macrolide, tetracycline, β-lactam) · NIV.

  • Antibiotics: ↑ dyspnea + ↑ sputum volume + ↑ sputum purulence, or on NIV/MV
  • NIV: pH ≤7.35 + PaCO2 ≥45 · severe dyspnea · persistent hypoxemia
03

Bronchiectasis & Cystic Fibrosis

▾
Clinical Picture

Productive cough · hemoptysis · dyspnea · fatigue · rhinosinusitis · wheezing · chest pain · clubbing · recurrent chest infections (Pseudomonas, aspergillus, non-TB mycobacteria).

  • Causes: recurrent pneumonia · TB · idiopathic · immunodeficiency · CF · CTD · IBD · ABPA · aspiration · congenital · A1AD · primary ciliary dyskinesia · tumor · foreign body · COPD
  • HRCT › airway diameter greater than accompanying vessel · lack of distal airway tapering · bronchial wall thickening · cysts
  • PFTs › obstructive
  • Workup: sputum CS · sputum AFB · ABPA screen · IgG/IgA/IgM · HIV · RF · anti-CCP · ANA · ANCA
Management

Treat the underlying cause.

  • Airway clearance: bronchodilators · positive expiratory pressure devices · postural drainage · manual techniques · inhaled hypertonic saline · exercise
  • Pulmonary rehab · vaccinations · LTOT (same indications as COPD)
  • PsA colonization › inhaled colistin/gentamicin
  • Recurrent exacerbations (≥2/y) › long-term azithromycin · DPP1i brensocatib
  • Localized disease › lung resection
  • Lung transplant: massive hemoptysis · severe PH · ICU admissions / respiratory failure
Acute Exacerbation

Antibiotics ×14 d (empiric fluoroquinolone). Major hemoptysis › IV antibiotics · tranexamic acid · embolization.

Hemoptysis — localize, protect the airway, then stop the bleeding.
Hemoptysis
  • Common causes: bronchitis · bronchogenic carcinoma · bronchiectasis
  • Workup: CBC (platelets) · coagulation · CXR · CT chest · fiberoptic bronchoscopy · CTA
  • Single lung › position with bleeding lung dependent
  • Airway compromise › MV
Clinical Picture

Recurrent/persistent respiratory infections (Pseudomonas, S aureus, H influenzae, Burkholderia cepacia) · bronchiectasis · hyperinflation · chronic sinusitis with nasal polyps · chronic/recurrent pancreatitis · clubbing · DM · infertility · malabsorption · steatorrhea.

  • Diagnosis: sweat chloride test › genetic testing
Management
  • Vaccinations · chest physiotherapy
  • Advanced lung/liver disease › transplantation
  • Exacerbation › antipseudomonal antibiotics
  • Chronic infection › nebulized tobramycin
  • Airway secretions › nebulized dornase alfa or hypertonic saline
  • Nocturnal hypoxemia/hypercapnia › nighttime BiPAP
  • Pancreatic insufficiency/malabsorption › pancreatic enzyme replacement · fat-soluble vitamin supplementation
  • Airway obstruction › inhaled bronchodilators, ICS
04

Pleural Disease

▾
  • Small effusion › US chest
  • Thoracentesis › suspected exudate · parapneumonic · new/unexplained
    • Send: cytology ×2 · Gram stain · AFB · LDH · Glu · cell count + differential · amylase
Light's Criteria — Exudate if ANY

Pleural:serum protein >0.5 · pleural:serum LDH >0.6 · pleural LDH >200 or >2/3 ULN serum LDH.

Transudate: HF, cirrhosis.  Exudate: parapneumonic, malignancy.

Fluid Analysis Patterns

What the differential points to

FindingDifferential
Blood (RBC ≥5000)malignancy · pulmonary infarction · asbestos-related
PMN >50,000, pH <7.2complicated parapneumonic · empyema (pus, Gram stain +ive)
Lymphocytosis >85%TB (adenosine deaminase) · lymphoma · malignancy · yellow nail · sarcoidosis · RA
Chylothorax (Tg >1.24, chylomicrons)lymphoma · trauma · surgery · TB · lymphangioleiomyomatosis
Eosinophiliaasbestos-related · nitrofurantoin · lung cancer · parasitic · PE · EGPA
Glu <3 or <0.5 serumRA · empyema · malignancy · TB · SLE · esophageal rupture
Pleural:serum amylase >1pancreatic disease · esophageal rupture
Caution — Lymphangioleiomyomatosis

Young female · cystic lung disease / pneumothorax · renal angiomyolipomas.

Chest Drain Indications

Frank pus · pH ≤7.2 · pH 7.2–7.4 + LDH >900 · Glu <3.3 · Gram stain +ive › IV antibiotics 5–7 d then PO ×2–6 weeks.

Rapidly recurrent malignant › pleurodesis (expandable lung) or indwelling pleural catheter (non-expandable lung).  −ive cytology › thoracoscopy + pleural biopsy.

  • Chest pain · dyspnea › CXR
Primary Pneumothorax

RF: smoking · FH · Marfan · thoracic endometriosis · tall male · subpleural blebs/bullae.

  • Minimal symptoms › conservative management
  • High-risk features (tension, significant hypoxia, bilateral, age >50 y + smoker, hemopneumothorax) › small-bore chest drain
  • >2 cm or significant symptoms › needle aspiration
  • Second ipsilateral occurrence › pleurodesis
  • Secondary: COPD (emphysema) · CF · TB · PJP · LAM › chest drain + pleurodesis
Tension Pneumothorax

Hypotension · hypoxia · tracheal deviation · absent breath sounds. Unstable › emergent needle decompression + chest drain (clinical diagnosis — do not wait for imaging).

Contraindications After Resolution

Scuba diving — lifelong.  Air travel — for 7 d from resolution on CXR.

05

Interstitial Lung Disease

▾
Clinical Picture

Subacute/chronic, progressive dyspnea · cough · end-inspiratory fine crepitations · inspiratory squeak · desaturation on ambulation.

  • Causes: CTD · occupational · drugs · sarcoidosis · hypersensitivity pneumonitis · IIP · lymphangioleiomyomatosis · pulmonary Langerhans cell histiocytosis · pulmonary alveolar proteinosis · radiation · post-COVID-19
  • IIP types: IPF · NSIP · cryptogenic organizing pneumonia · acute interstitial pneumonia · lymphocytic interstitial pneumonia · desquamative interstitial pneumonia
  • CXR › interstitial reticular/nodular infiltrates · PFT › restrictive, low DLCO
  • Serology: CRP · ESR · ANA · RF · myositis panel · anti-CCP
General Management

Smoking cessation · pulmonary rehab · vaccinations · lung transplant (FVC <80%, DLCO <40%). Resting hypoxemia › supplemental O2. Persistent dyspnea/cough › low-dose opioids.

Subtypes — HRCT & Treatment

Pattern recognition drives therapy

SubtypeHRCT patternKey features & treatment
IPFUIP — reticular, subpleural/basal, honeycombingage 50–70 y · clubbing › anti-fibrotic (nintedanib, pirfenidone, nerandomilast)
NSIPbilateral lower-lobe reticular · ground-glassyounger · better prognosis › anti-fibrotic, immunosuppression
HPupper-lobe predominant · ground-glass · nodules · 3-density sign · fibrosissymptoms ≤12 h after organic antigen · fever · fatigue › avoid antigen; severe › steroids, MMF/AZA
Pneumoconiosis—asbestos, silica › avoid exposure
SARD-ILD—SSc, RA, IIM, Sjögren's, MCTD › treat underlying cause, anti-fibrotic
Drug-induced—MTX, amiodarone, bleomycin, nitrofurantoin, vaping › DC drug, steroids
COPCXR patchy opacities; HRCT ground-glass + alveolar consolidationsubacute · cough · fever · malaise · fails to respond to antibiotics › glucocorticoids
RB-ILDupper-lobe ground-glass · centrilobular nodulessmokers › smoking cessation › glucocorticoids
Radiation pneumonitisground-glass within radiation field4–12 wk post-radiation · fever · pleuritic pain · fatigue · weight loss › severe: GC
AIPbilateral alveolar opacitiesrapid · respiratory failure · ↑ mortality › MV, critical care
CPFEemphysema upper lobes + fibrosis lower lobesemphysema + fibrosis · PH › lung transplant

Sarcoidosis

A multisystem granulomatous mimic of ILD
Clinical Picture

Constitutional: fever · weight loss · night sweats · dry cough · dyspnea.

Organ involvement: pulmonary · cutaneous (lupus pernio, erythema nodosum) · cardiac (CM, arrhythmia, heart block) · CNS (CN palsy, optic neuritis, headache, ataxia, weakness) · ocular (anterior uveitis) · liver · spleen · MSK · kidney · hypercalcemia.

Classic Syndromes

Löfgren: bilateral hilar lymphadenopathy + erythema nodosum + migratory polyarthralgias + fever · female › spontaneous remission.

Heerfordt: anterior uveitis + parotid enlargement + fever + facial palsy.

CXR Staging

Bilateral hilar lymphadenopathy is the hallmark

StageFindings
Stage 1bilateral hilar lymphadenopathy
Stage 2lymphadenopathy + parenchymal disease
Stage 3parenchymal disease only
Stage 4fibrosis
  • Biopsy (lymph node/transbronchial) › non-caseating granulomas
  • 2/3 undergo spontaneous remission ≤10 y
  • Cardiac workup › ECG · echo · CMR/PET
  • Hypercalcemia › low PTH · high vit D
Glucocorticoid Indications

Extrapulmonary disease · significant pulmonary symptoms · progressive PFT decline · hypercalcemia.

  • Pulmonary › glucocorticoids or MTX
  • Erythema nodosum › NSAIDs
  • Lupus pernio or anterior uveitis › topical steroids
06

Sleep Medicine

▾
  • Daytime sleepiness › actigraphy / sleep diary
Obstructive Sleep Apnea

Excessive daytime sleepiness · nocturnal choking/gasping · morning headaches · snoring › weight loss · avoid alcohol/sedatives/opioids before bed · lateral sleeping position.

RF: BMI >30 · neck circumference >17 in · enlarged/elongated soft palate.

AHI Severity & Treatment

HSAT / polysomnography — AHI ≥5/h defines OSA

SeverityAHI (events/h)
Mild5–15
Moderate15–30
Severe>30
  • Treatment (symptomatic, HTN, or severe) › CPAP/APAP · surgery
  • PAP → xerostomia / nasal congestion › heated humidification
  • Mild/moderate › oral appliances
  • BMI ≥35 › bariatric surgery
Obesity Hypoventilation Syndrome (OHS)

Daytime PaCO2 >45 · HCO3 >27 › polycythemia, RVF, PH. Manage with weight loss · CPAP · supplemental O2.

07

Pulmonary Hypertension

▾
Clinical Picture

Exertional dyspnea · decreased exercise tolerance · syncope/pre-syncope · chest pain · lower-limb edema · signs of RV failure.

  • Workup: TTE (RA/RV dilatation, TR, mean PA pressure) · PFT (isolated ↓DLCO) · left heart catheterization + CAG (LV dysfunction) · HRCT (ILD) · CTD testing · LFTs · HIV · V/Q
Right Heart Catheterization — Diagnostic Criteria

Mean PAP >20 mmHg · PCWP ≤15 mmHg · pre-capillary PVR >2.

WHO Groups

Mechanism dictates therapy

GroupCauses & treatment
1 - PAHidiopathic · heritable · drug/toxin · CTD (limited cutaneous SSc) · HIV · schistosomiasis · PVOD › PDE5i + ERA (ambrisentan, macitentan) › lung/heart-lung transplant
2 - Left heart diseasesystolic/diastolic dysfunction · valvular disease › treat underlying cause
3 - Lung diseaseCOPD · ILD › treat underlying cause
4 - Chronic thromboemboliclifelong anticoagulation + pulmonary thromboendarterectomy; non-operative/persistent › riociguat
5 - Miscellaneousmyeloproliferative disease · splenectomy · sarcoid · LCH · LAM › treat underlying cause
Group 1 — Additional Notes
  • Vasoreactivity testing +ive › CCB
  • Avoid pregnancy
  • SpO2 ≤90% › O2 therapy
Signs of RV Failure

Dyspnea · LL edema · RV heave · widely split S2 · S3 gallop · increased P2 · ↑JVP (large a wave) · TR.