Bronchoalveolar Lavage (BAL)

Classification of Lower Respiratory Sampling Techniques

A. Bronchoscopic Techniques

(Performed using fiberoptic bronchoscope)

1. Bronchoalveolar lavage (BAL)
2. Protected specimen brush (PSB / Protected brush)
3. Bronchial wash
4. Transbronchial biopsy (TBB)
5. Endobronchial biopsy

B. Non-Bronchoscopic Techniques

(Blind catheter-based techniques)

1. Mini-BAL (Blind BAL)
2. Blind protected brush
3. Endotracheal aspirate (ETA)

Bronchoalveolar lavage (BAL) is a diagnostic bronchoscopic procedure in which sterile isotonic saline is instilled into a subsegmental bronchus and then aspirated to obtain alveolar epithelial lining fluid, containing:

• Alveolar macrophages
• Lymphocytes
• Neutrophils
• Eosinophils
• Microorganisms
• Malignant cells
• Proteinaceous material

—> BAL reflects distal airway + alveolar pathology, unlike bronchial wash which samples proximal airways.

Objectives / Rationale

BAL is used to:

1. Identify infectious etiology
2. Characterize inflammatory cell pattern
3. Diagnose diffuse lung diseases
4. Detect alveolar hemorrhage
5. Assess malignancy
6. Evaluate immune-mediated lung disease

Anatomy Sampled by BAL

Indications of BAL

1. Infectious Indications (Most common in ICU)

Immunocompromised host

• Pneumocystis jirovecii pneumonia (PCP)
• CMV pneumonia
• Invasive aspergillosis
• Nocardia
• TB (smear / GeneXpert)
• Fungal pneumonias

Non-resolving pneumonia

• Ventilator-associated pneumonia (VAP)
• HAP with negative sputum cultures

Unexplained fever + pulmonary infiltrates

2. Interstitial Lung Diseases (ILD)

BAL helps support diagnosis, not replace biopsy.

3. Acute Hypoxemic Respiratory Failure

• Acute respiratory distress syndrome (ARDS)
• Acute interstitial pneumonia
• Acute exacerbation of ILD
• Suspected alveolar hemorrhage

4. Suspected Malignancy

• Bronchoalveolar carcinoma (lepidic adenocarcinoma)
• Lymphoma
• Lymphangitic carcinomatosis

5. Special Situations

• Pulmonary alveolar proteinosis (milky BAL)
• Lipoid pneumonia (lipid-laden macrophages)
• Aspiration pneumonitis

Contraindications

Absolute Contraindications

• Severe refractory hypoxemia (PaO₂ < 60 mmHg on FiO₂ > 0.8)
• Unstable hemodynamics
• Life-threatening arrhythmias
• Uncorrected severe coagulopathy
• Raised ICP (relative but exam favorite)

Relative Contraindications

• Platelets < 50,000
• INR > 1.5
• Severe pulmonary hypertension
• Recent MI
• Poor tolerance to bronchoscopy

Pre-Procedure Preparation

Patient Evaluation

• ABG
• Chest imaging (localize lesion)
• Coagulation profile
• Platelet count
• Oxygenation status

Ventilated Patients

• FiO₂ → 100% before procedure
• PEEP optimized
• Closed suction bronchoscopy preferred

Technique of BAL (Step-by-Step)

1. Bronchoscope Positioning

• Wedged into a subsegmental bronchus
• Common sites:
• Right middle lobe
• Lingula
  (best yield due to gravity-dependent alveoli)

2. Instillation of Saline

• Sterile 0.9% normal saline
• Volume per aliquot: 20–50 mL
• Total volume: 100–300 mL (usually 100–150 mL)

3. Aspiration

• Gentle suction (low negative pressure)
• Expected recovery: 40–60% of instilled volume

4. Sample Handling

• First aliquot → microbiology (higher contamination)
• Later aliquots → cytology, cell counts

BAL Fluid Analysis

1. Gross Appearance 

2. Cellular Differential (Normal BAL)

3. Abnormal Patterns 

4. Microbiological Tests

• Gram stain
• Bacterial culture
• AFB smear & culture
• GeneXpert MTB/RIF
• Fungal smear & culture
• Galactomannan (aspergillus)
• PCR for viruses
• Silver stain (PCP)

5. Special Tests

• PAS stain → alveolar proteinosis
• Oil Red O → lipoid pneumonia
• Cytology → malignancy
• Iron stain → alveolar hemorrhage

BAL in ICU / Ventilated Patient

Key Points

• Transient hypoxemia common
• Increase FiO₂ & PEEP temporarily
• Perform quickly
• Monitor:
• SpO₂
• BP
• ECG

Complications

BAL vs Bronchial Wash vs Biopsy

BAL in Specific Diseases 

• PCP → BAL sensitivity > 90%
• DAH → Sequential aliquots increasingly bloody
• Sarcoidosis → Lymphocytosis + high CD4/CD8
• HP → Marked lymphocytosis + low CD4/CD8
• IPF → Neutrophilia ± eosinophils
• PAP → Milky BAL + PAS positive

2. Protected Specimen Brush (PSB)

Definition

A bronchoscopic sampling method using a double-sheathed sterile brush designed to prevent contamination from upper airway flora.

Mechanism

• Brush enclosed in catheter sheath
• Outer sheath protects brush during insertion
• Brush exposed only at target bronchial segment
• Specimen transferred to sterile container

Sampling Site

• Distal bronchi
• NOT alveoli (unlike BAL)

Quantitative Diagnostic Cutoff

• ≥10³ CFU/mL → Suggests infection

Advantages

• Minimal contamination
• High specificity for VAP
• Useful when colonization suspected

Limitations

• Smaller sample volume
• Cannot assess cellular patterns
• Lower sensitivity than BAL

3. Bronchial Washing

Definition

Instillation of small saline volume into proximal bronchial tree and suction retrieval.

Characteristics

• Samples large airways
• Less invasive than BAL
• Mainly used for:

Indications

• Endobronchial tumors
• Proximal airway infections
• Cytology for malignancy

Diagnostic Yield

Lower than BAL for alveolar diseases.

4. Mini-BAL (Blind BAL / Non-Bronchoscopic BAL)

Definition

Lower airway sampling using a catheter passed blindly through endotracheal tube.

Technique

• Special catheter inserted via ETT
• Advanced until resistance
• Saline instilled (20–60 mL)
• Aspirated back

Sampling Area

Distal airway and alveoli (approximate)

Quantitative Cutoff

• ≥10⁴ CFU/mL

Advantages

• Does NOT require bronchoscope
• Bedside ICU procedure
• Less hemodynamic disturbance
• Safer in unstable patients

Limitations

• Blind sampling
• Possible contamination
• Cannot visualize airway

5. Blind Protected Brush

Definition

Blind catheter-based version of PSB.

Features

• Similar contamination prevention as PSB
• Performed without bronchoscope
• Used in ventilated patients

Diagnostic Cutoff

• ≥10³ CFU/mL

6. Endotracheal Aspirate (ETA)

Definition

Suction sampling via endotracheal tube.

Features

• Simplest technique
• Non-invasive
• High sensitivity
• Low specificity

Uses

• Initial screening in VAP
• Monitoring colonisation

Limitations

• High contamination risk
• Cannot distinguish infection vs colonization reliably

Comparison Table