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Lung Abscess & Pulmonary Gangrene

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Lung Abscess

Definition

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Classification

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Etiology & Microbiology

• Anaerobes are implicated in ~90% of cases — typically 3–6 isolates per sample are identified (Harrison's, p. 5087). Common organisms include Fusobacterium nucleatum, Prevotella, Peptostreptococcus, and Bacteroides species.
• Aerobic organisms can also cause abscesses independently: Staphylococcus aureus (including MRSA), Klebsiella pneumoniae, Pseudomonas aeruginosa, Streptococcus milleri group.
• Fungal/parasitic causes (less common): Aspergillus, Entamoeba histolytica, Nocardia.

• Poor dental hygiene / dental infection (often antecedent)
• Alcohol use disorder
• Altered consciousness (seizures, general anesthesia, stroke)
• Dysphagia, esophageal disease

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Pathophysiology

1. Aspiration of oropharyngeal/gastric contents → colonization of dependent lung segments
2. Pneumonitis → tissue necrosis due to bacterial toxins and ischemia
3. Liquefaction of necrotic tissue → cavity formation
4. If communication established with bronchus → air-fluid level appears

• Posterior segments of upper lobes
• Superior segments of lower lobes (when aspiration occurs supine)

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Clinical Features

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Imaging

• Thick-walled cavity, often in dependent segments
• Air-fluid level within the cavity (pathognomonic when present)
• Surrounding consolidation

• Better delineates cavity wall thickness, internal contents, satellite lesions
• Distinguishes abscess from empyema with bronchopleural fistula

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Differential Diagnosis

• Necrotizing pneumonia (more diffuse, multiple small cavities)
• Empyema with bronchopleural fistula (lenticular shape, obtuse pleural angle on CT)
• Pneumatocele (thin-walled, post-infectious)
• Cavitating malignancy (irregular inner wall, no air-fluid level)
• Pulmonary tuberculosis (upper lobe, bilateral, systemic features)
• Wegener's granulomatosis / GPA (multiple nodules with cavitation)

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Management

Antibiotics (Mainstay)

• First-line: Amoxicillin-clavulanate or clindamycin (anaerobic coverage)
• Alternatives: Metronidazole + penicillin, or carbapenems for resistant organisms
• Duration: Typically 4–6 weeks, continued until cavity resolves or stabilizes on imaging
• For S. aureus (MRSA): add vancomycin or linezolid

Postural Drainage

• Positioning to facilitate gravity drainage through communicating bronchus

Bronchoscopy

• Diagnostic: cultures, rule out obstructing lesion/malignancy
• Therapeutic: drainage of abscess contents in selected cases

Surgery

• Reserved for failure of medical therapy (4–6 weeks), massive hemoptysis, or suspected malignancy
• Procedures: lobectomy, pneumonectomy, or CT-guided percutaneous drainage

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Complications

• Bronchopleural fistula
• Empyema thoracis
• Hemoptysis (sometimes massive)
• Septicemia
• Progression to pulmonary gangrene (see below)
• Amyloidosis (chronic cases)

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Prognosis

• Overall mortality ~5–10% with appropriate therapy
• Worse prognosis: elderly, immunocompromised, large abscesses (>6 cm), S. aureus or gram-negative etiology, obstruction by malignancy

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Pulmonary Gangrene

Definition

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Pathophysiology

1. Massive bacterial invasion → intense inflammatory response
2. Thrombosis of pulmonary vasculature (arteries and veins) → ischemia
3. Loss of blood supply + bacterial destruction → gangrene (wet necrosis) of entire lobes or the whole lung
4. Sloughing of necrotic lung tissue → pulmonary sequestrum (free-floating necrotic tissue within a cavity — the hallmark)

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Etiology

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Clinical Features

• Acute, rapidly deteriorating course (unlike subacute lung abscess)
• High fever, rigors, profound toxemia
• Copious foul, bloody, necrotic sputum
• Rapid respiratory failure
• Septic shock

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Imaging Hallmarks

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Comparison: Lung Abscess vs. Pulmonary Gangrene

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Management

1. Aggressive IV antibiotics — broad-spectrum covering gram-positive, gram-negative, and anaerobes (e.g., piperacillin-tazobactam + vancomycin ± metronidazole)
2. Supportive care: ICU-level, mechanical ventilation as needed
3. Surgery (often required):
   • Pneumonectomy or lobectomy for gangrene of a lobe/lung
   • CT-guided drainage for accessible collections
4. Anticoagulation: considered in selected cases due to vascular thrombosis, though evidence is limited

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Prognosis

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Summary

• Lung abscess = focal, subacute, predominantly anaerobic → responds well to prolonged antibiotics
• Pulmonary gangrene = lobar/diffuse, fulminant, virulent aerobic organisms, vascular thrombosis → high mortality, often requires surgery

Chronic Obstructive Pulmonary Disease (COPD)

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Definition

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Epidemiology

• One of the leading causes of morbidity and mortality worldwide (3rd leading cause of death globally)
• Affects ~10% of adults over 40
• Significantly underdiagnosed — many patients present only when disease is advanced

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Etiology & Risk Factors

Environmental (Dominant)

• Cigarette smoking — accounts for ~80–90% of cases in developed countries; pack-year history is the strongest risk factor
• Biomass fuel smoke — cooking/heating fires; major cause globally, especially in women in low-income countries
• Occupational dusts/chemicals — coal dust, silica, grain dust, isocyanates
• Air pollution — outdoor (PM2.5, NO₂) and indoor

Host Factors

• Alpha-1 antitrypsin (AAT) deficiency — genetic risk; panacinar emphysema, especially in lower lobes; onset in younger non-smokers
• Abnormal lung development — low birth weight, prematurity, childhood respiratory infections
• Airway hyperresponsiveness — asthma–COPD overlap
• Genetics — multiple susceptibility loci beyond AAT

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Pathophysiology

Noxious Exposure
       ↓
Chronic Airway Inflammation (neutrophils, macrophages, CD8+ T cells)
       ↓
┌────────────────────────────────────────┐
│  Airway remodeling (small airways)     │  → Airflow obstruction
│  Mucus hypersecretion                  │  → Chronic bronchitis
│  Alveolar wall destruction (elastase > │
│  anti-elastase imbalance)              │  → Emphysema
└────────────────────────────────────────┘
       ↓
Air trapping → Hyperinflation → ↑ Work of breathing
       ↓
V/Q mismatch → Hypoxemia → Hypercapnia (late)
       ↓
Pulmonary hypertension → Cor pulmonale

• Protease–antiprotease imbalance: excess neutrophil elastase and MMPs destroy alveolar parenchyma
• Oxidative stress: amplifies inflammation
• Loss of elastic recoil: dynamic airway collapse on expiration (air trapping)

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Clinical Features

Symptoms

Signs

• Barrel chest (increased AP diameter) — emphysema
• Hyperresonance on percussion
• Diminished breath sounds, prolonged expiration
• Use of accessory muscles, pursed-lip breathing
• Cyanosis (central) — advanced disease
• Cor pulmonale: elevated JVP, peripheral edema, right ventricular heave

Classic Phenotypes

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Diagnosis

Spirometry (Mandatory)

• Post-bronchodilator FEV₁/FVC < 0.70 confirms airflow obstruction
• FEV₁ % predicted classifies severity

GOLD Spirometric Grading

GOLD ABE Assessment (2023 Update)

Other Investigations

• CXR: hyperinflation, flattened diaphragms, bullae, increased retrosternal airspace
• HRCT chest: better characterizes emphysema subtype, bullae, bronchiectasis
• ABG: hypoxemia, hypercapnia in advanced disease
• Alpha-1 antitrypsin level: screen all patients with COPD (especially age <45 or minimal smoking history)
• ECG/Echo: assess for cor pulmonale
• 6-minute walk test: functional assessment
• CBC: secondary polycythemia

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Imaging

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Management

Non-Pharmacological (Foundation)

• Smoking cessation — single most effective intervention; slows disease progression
• Pulmonary rehabilitation — improves dyspnea and exercise capacity
• Vaccination: influenza (annual), pneumococcal, COVID-19, RSV
• Nutritional support — address cachexia
• Oxygen therapy: Long-term O₂ (LTOT) if PaO₂ ≤55 mmHg or SaO₂ ≤88% at rest → improves survival

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Pharmacological — Stable COPD (GOLD 2023)

Bronchodilators (Mainstay)

Inhaled Corticosteroids (ICS)

• ICS + LABA: indicated when eosinophil count ≥300/µL or Group E despite dual bronchodilation
• Triple therapy (ICS + LABA + LAMA): for persistent exacerbations; reduces mortality (IMPACT trial)
• Caution: increased pneumonia risk with ICS

Other Agents

• Roflumilast (PDE-4 inhibitor): oral; for severe COPD with chronic bronchitis phenotype and frequent exacerbations (FEV₁ <50%)
• Azithromycin (long-term): reduces exacerbation frequency in select patients; monitor for hearing loss and cardiac QTc prolongation
• Mucolytics (NAC, carbocisteine): may reduce exacerbations in some patients
• AAT augmentation therapy: IV infusion for confirmed AAT deficiency with emphysema

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Initial Treatment Algorithm (GOLD 2023)

Group A → SABA or SAMA (PRN)
Group B → LABA + LAMA (dual bronchodilation)
Group E → LABA + LAMA ± ICS (if eos ≥300)

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Acute Exacerbations of COPD (AECOPD)

Definition

Causes

• Respiratory infections (bacterial: H. influenzae, S. pneumoniae, M. catarrhalis; viral: rhinovirus, influenza)
• Air pollution
• Non-compliance with therapy
• Pulmonary embolism (must exclude)

Management of AECOPD

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Complications

• Cor pulmonale and right heart failure
• Respiratory failure (Type I and Type II)
• Pneumothorax (especially with bullous disease)
• Pulmonary hypertension
• Secondary polycythemia
• Malnutrition and cachexia
• Anxiety and depression (significantly underdiagnosed)
• Lung cancer (shared risk factors)

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Surgical/Interventional Options

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Prognosis & Prognostic Tools

BODE Index (predicts mortality)

• Smoking cessation and LTOT are the only interventions proven to reduce mortality in stable COPD (along with triple therapy showing mortality benefit in Group E)
• 5-year mortality after first hospitalization for AECOPD: ~50%

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Key Takeaways

1. Spirometry is mandatory for diagnosis — clinical features alone are insufficient
2. LAMA is the preferred initial maintenance bronchodilator for most patients
3. ICS should not be used as monotherapy in COPD; reserve for specific indications (high eosinophils, frequent exacerbations)
4. Target SpO₂ 88–92% during exacerbations — avoid suppressing hypoxic drive
5. Smoking cessation at any stage alters the natural history
6. Screen all COPD patients for AAT deficiency

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1. Bronchial Asthma

Definition

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Pathophysiology

Allergen / Trigger exposure
         ↓
Th2-mediated immune response
→ IL-4, IL-5, IL-13 release
→ IgE production (sensitization)
         ↓
Mast cell & eosinophil activation
         ↓
┌─────────────────────────────────────────┐
│  Bronchoconstriction (acute, reversible) │
│  Airway mucosal edema                    │
│  Mucus hypersecretion                    │
│  Airway remodeling (chronic)             │
└─────────────────────────────────────────┘
         ↓
Airflow obstruction → Wheeze, dyspnea, chest tightness

• Subepithelial fibrosis
• Smooth muscle hypertrophy
• Goblet cell hyperplasia
• Angiogenesis

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Classification of Severity (GINA / NAEPP)

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Triggers

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Clinical Features

• Episodic wheeze, dyspnea, chest tightness, cough (often worse at night/early morning)
• Symptoms vary and are reversible
• Between attacks: patient may be completely asymptomatic
• Diurnal variation: PEF lowest in early morning ("morning dipping")

• Tachypnea, tachycardia
• Prolonged expiration, expiratory wheeze
• Use of accessory muscles
• Pulsus paradoxus (>10 mmHg drop in SBP on inspiration — indicates severe attack)
• Silent chest = very severe (no air movement)

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Diagnosis

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Management (GINA 2023 Stepwise Approach)

Controller + Reliever Therapy

Key GINA 2023 update: SABA-alone reliever is no longer recommended at any step. ICS-containing reliever (ICS-formoterol) is preferred to reduce exacerbation risk.

Biologic Therapies (Step 5, Severe Asthma)

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Acute Severe Asthma (Status Asthmaticus)

Severity Assessment

Treatment

1. Oxygen: Target SpO₂ 94–98%
2. Nebulized SABA: Salbutamol 2.5–5 mg, repeat every 20 min × 3
3. Ipratropium bromide: add to SABA in severe attack
4. Systemic corticosteroids: Prednisolone 40–50 mg PO or IV hydrocortisone 100 mg QID
5. IV magnesium sulfate: 1.2–2 g IV over 20 min for severe/life-threatening attack
6. IV aminophylline: second-line
7. Heliox: reduces turbulent airflow in critical obstruction
8. NIV/Intubation: last resort — intubation in asthma is high risk (dynamic hyperinflation)

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2. Upper Airway Obstruction (UAO)

Definition

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Classification

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Causes

Acute UAO (Emergencies)

Chronic UAO

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Pathophysiology of Airflow Dynamics

• Flow-volume loop is diagnostic: flattening of the inspiratory limb (extrathoracic), expiratory limb (intrathoracic), or both (fixed)

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Clinical Features

• Stridor (inspiratory = supraglottic/glottic; biphasic = subglottic/tracheal)
• Dyspnea, use of accessory muscles
• Hoarseness, dysphonia, dysphagia
• Cyanosis and altered consciousness in severe obstruction
• Paradoxical breathing (chest sucks in on inspiration) in complete obstruction

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Diagnosis

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Management

Emergency

Definitive / Chronic

• Tracheostomy: bypasses obstruction; emergency or elective
• Tracheal dilation/stenting: post-intubation stenosis
• Surgery: laryngeal carcinoma (laryngectomy), goiter, tumor resection
• CPAP: obstructive sleep apnea
• Voice therapy / reinnervation: vocal cord paralysis

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3. Pulmonary Edema

Definition

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Classification: Cardiogenic vs. Non-Cardiogenic

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Pathophysiology

Cardiogenic

LV dysfunction / ↑ filling pressures
       ↓
↑ Pulmonary capillary wedge pressure (>18 mmHg)
       ↓
Fluid transudation: interstitium → alveoli
       ↓
Interstitial edema → Alveolar flooding
       ↓
V/Q mismatch → Hypoxemia → Dyspnea

Non-Cardiogenic (ARDS)

Systemic/pulmonary insult (sepsis, aspiration)
       ↓
Endothelial injury + inflammatory mediators
       ↓
↑ Capillary permeability
       ↓
Protein-rich exudate floods alveoli
       ↓
Surfactant destruction → Alveolar collapse
       ↓
Refractory hypoxemia (P/F ratio <300)

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Clinical Features

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Imaging

Radiological Stages of Pulmonary Edema (Cardiogenic)

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Diagnosis

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Management

Cardiogenic Pulmonary Edema (Acute)

Non-Cardiogenic (ARDS) Management

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4. Nutrition in COPD

Why Nutrition Matters in COPD

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Mechanisms of Malnutrition in COPD

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Consequences of Malnutrition in COPD

• Muscle wasting (sarcopenia) → reduced respiratory muscle strength → ventilatory failure
• Impaired immune function → increased susceptibility to infections/exacerbations
• Reduced exercise capacity and quality of life
• Osteoporosis (compounded by corticosteroid use)
• Increased hospital admissions and mortality
• BMI <21 kg/m² is an independent predictor of mortality (component of BODE index)

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Nutritional Assessment

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Nutritional Requirements in COPD

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Dietary & Practical Recommendations

• Small, frequent meals (4–6 meals/day) — reduces post-meal dyspnea and bloating
• Eat main meals when least breathless (often earlier in the day)
• Avoid gas-forming foods (carbonated drinks, beans, cabbage) — worsen diaphragmatic compression
• Bronchodilators before meals — reduce dyspnea during eating
• Supplemental oxygen during meals if SpO₂ drops on eating
• High-calorie, high-protein oral supplements (e.g., Ensure, Fortisip) if inadequate oral intake
• Dental care — poor dentition is common and limits food intake

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Nutritional Support Algorithm

Screen all COPD patients (BMI, weight trend, muscle mass)
         ↓
BMI <21 or unintentional weight loss >10% in 6 months?
         ↓
YES → Dietary counseling + high-calorie, high-protein diet
         ↓
Inadequate with diet alone?
         ↓
YES → Oral nutritional supplements (ONS)
         ↓
Unable to meet needs orally (severe, mechanically ventilated)?
         ↓
Enteral nutrition (nasogastric/PEG)
    ↓
Use high-fat, low-carbohydrate enteral formula (e.g., Pulmocare)
to minimize CO₂ production

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Pulmonary-Specific Enteral Formulas

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Exercise + Nutrition: Synergistic Effect

• Pulmonary rehabilitation + nutritional supplementation together are more effective than either alone for improving muscle mass, 6-minute walk distance, and quality of life
• Anabolic agents (testosterone, megestrol acetate) explored in severe sarcopenia but evidence remains limited

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Summary Table

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1. Pleural Effusion

Definition

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Anatomy & Physiology of the Pleural Space

• Fluid normally enters via the parietal pleura (systemic capillaries) and drains via lymphatics
• Effusion occurs when:
  • Fluid production exceeds drainage (↑ hydrostatic pressure or ↑ capillary permeability)
  • Lymphatic drainage is impaired
  • Fluid enters from adjacent compartments (abdomen, chest wall)

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Classification: Transudate vs. Exudate

Light's Criteria (1972 — Gold Standard)

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Causes

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Clinical Features

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Investigations

Imaging

• Small effusion (>200 mL): blunting of costophrenic angle
• Moderate: homogeneous basal opacity with meniscus sign
• Large: complete hemithorax opacification with contralateral mediastinal shift
• Subpulmonic effusion: apparent elevated hemidiaphragm

• Detects as little as 20 mL
• Guides thoracentesis (current standard of care — Harrison's, p. 7875)
• Distinguishes free fluid from loculated/solid

• Identifies underlying cause (malignancy, lymphadenopathy, loculations)
• Characterizes effusion (simple, complex, empyema)

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Pleural Fluid Analysis

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Management

General Approach

Pleural effusion detected
        ↓
Clinical context clear? (e.g., bilateral effusions + CHF)
        ↓
YES → Treat underlying cause first
        ↓
No response or unilateral/exudative features?
        ↓
Thoracentesis (diagnostic ± therapeutic)
        ↓
Analyze fluid → Light's criteria + full panel
        ↓
Guide specific management

Specific Management

Pleurodesis

• Aims to obliterate pleural space by inducing inflammation/fibrosis
• Agents: Talc (most effective), bleomycin, doxycycline
• Indication: recurrent malignant or benign symptomatic effusions

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2. Dry Pleuritis (Fibrinous Pleuritis)

Definition

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Pathophysiology

Pleural injury / inflammation
        ↓
Increased vascular permeability → fibrin-rich exudate
        ↓
Fibrin deposits on visceral + parietal pleura
        ↓
Roughened pleural surfaces rub together on breathing
        ↓
PLEURITIC CHEST PAIN (friction rub)
        ↓
If inflammation progresses → fluid accumulation → wet pleuritis (effusion)

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Causes

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Clinical Features

Symptoms

Signs

Key distinction: Pleural friction rub vs. pericardial friction rub — pleural rub disappears when patient holds breath; pericardial rub persists.

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Investigations

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Management

Symptomatic (Core Treatment)

Treat Underlying Cause

• Viral → supportive
• Bacterial pneumonia → antibiotics
• TB → anti-TB therapy
• PE → anticoagulation
• SLE/RA → disease-modifying agents, corticosteroids
• Uraemic pleuritis → dialysis

Patient Advice

• Rest, avoid exertion during acute phase
• Deep breathing exercises once pain controlled (prevent atelectasis)
• Splinting with pillow against chest wall when coughing

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3. Pneumothorax

Definition

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Classification

Pneumothorax
├── Spontaneous
│   ├── Primary (PSP) — no underlying lung disease
│   └── Secondary (SSP) — complicates existing lung disease
├── Traumatic — penetrating/blunt chest trauma, iatrogenic
└── Tension pneumothorax — air enters but cannot escape (one-way valve) → EMERGENCY

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Primary Spontaneous Pneumothorax (PSP)

• Young, tall, thin males (20–30 years)
• Due to rupture of apical subpleural blebs/bullae
• No underlying lung disease
• Smoking increases risk 20-fold
• Recurrence rate: ~30% first episode, ~60% after second

Secondary Spontaneous Pneumothorax (SSP)

• Complicates underlying lung pathology
• More serious — less reserve lung function

Iatrogenic Pneumothorax

• Central line insertion (subclavian/internal jugular)
• Thoracentesis, pleural biopsy
• Mechanical ventilation (barotrauma)
• CT-guided lung biopsy

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Tension Pneumothorax — EMERGENCY

One-way valve mechanism:
Air enters pleural space on inspiration → cannot exit on expiration
        ↓
Progressive ↑ intrapleural pressure
        ↓
Complete ipsilateral lung collapse
        ↓
Mediastinal shift → contralateral lung compression
        ↓
↓ Venous return → ↓ Cardiac output → Obstructive SHOCK
        ↓
DEATH if not immediately decompressed

• Severe respiratory distress + tachycardia
• Tracheal deviation away from affected side
• Absent breath sounds ipsilateral
• Hypotension + raised JVP (Beck's triad variant)
• Cyanosis

Do NOT wait for CXR in suspected tension pneumothorax — treat immediately.

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Clinical Features

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Investigations

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Imaging

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Size Estimation

BTS Classification

ACCP Classification

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Management

Tension Pneumothorax (Immediate)

1. Needle thoracostomy (emergency decompression):
   • 2nd intercostal space, midclavicular line — large-bore cannula (14G)
   • Definitive: chest tube insertion (5th ICS, anterior axillary line) immediately after
2. High-flow oxygen
3. Do NOT delay for imaging

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Spontaneous Pneumothorax — BTS Guidelines

Primary Spontaneous Pneumothorax (PSP)

PSP confirmed on CXR
        ↓
Breathless AND large (≥2 cm)?
        ↓
NO → Conservative management (discharge, review in 2–4 weeks)
        ↓
YES → Aspiration (16–18G cannula, 2nd ICS MCL)
        ↓
Successful (<2 cm residual, improved symptoms)?
        ↓
YES → Discharge + review        NO → Chest drain insertion

Secondary Spontaneous Pneumothorax (SSP)

SSP confirmed
        ↓
Any size SSP = hospital admission
        ↓
Small (<1 cm) + minimally symptomatic → Observation + O₂
        ↓
1–2 cm → Aspiration
        ↓
>2 cm OR failed aspiration → Chest drain

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Chest Drain Management

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Persistent Air Leak (>5–7 days)

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Indications for Surgery (VATS/Thoracotomy)

• Second ipsilateral pneumothorax
• First contralateral pneumothorax
• Bilateral simultaneous pneumothorax
• Persistent air leak >5–7 days despite chest drain
• Failure of lung to re-expand
• High-risk occupation (pilot, diver) — even after first episode
• Haemopneumothorax

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Oxygen Therapy in Pneumothorax

• High-flow 100% oxygen (reservoir mask) accelerates pleural air absorption 3–4 times faster than breathing room air (replaces nitrogen in pleural space with rapidly absorbed oxygen)
• Use with caution in SSP with COPD (target SpO₂ 88–92%)

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Complications

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Summary Comparison Table