Bronchoalveolar lavage (BAL)

Bronchoalveolar lavage (BAL) is a bronchoscopic sampling technique that instills sterile saline into a wedged distal airway and retrieves it for microbiological, cytological, and immunological analysis.

• It provides a direct window into the alveolar environment and outperforms proximal sampling techniques when distal pathology is suspected.
• BAL can be a useful diagnostic tool in critically ill patients for diagnosing pneumonia, diffuse infiltrates, alveolar haemorrhage, and immunocompromised hosts.
• Risk-benefit balance should be considered before performing BAL

INDICATIONS

• Suspected VAP or severe HAP
  • Lower contamination than endotracheal aspirates; supports antibiotic stewardship
• Non‑resolving or atypical pneumonia
  • Fungal, viral, mycobacterial, Pneumocystis, Nocardia
• Diffuse pulmonary infiltrates of unclear cause
  • Distinguish infection vs ARDS vs oedema vs eosinophilic lung disease
• Suspected alveolar haemorrhage
  • Progressively bloodier aliquots; ≥20% haemosiderin‑laden macrophages
• Immunocompromised host with new infiltrates
  • High yield for opportunistic pathogens

BAL is less useful for:

• Classic aspiration pneumonitis with rapid improvement
• Mild CAP responding to therapy
• Obvious cardiogenic pulmonary oedema
• Situations where results will not change management

CONTRAINDICATIONS

Absolute

• Severe hypoxaemia or haemodynamic instability where risk outweighs benefit

Relative

• high oxygen or PEEP requirements (e.g. FiO₂ >0.8 or PEEP >15–18 cmH₂O)
• Poor lung compliance / difficult to ventilate
• Severe bronchospasm
• Uncontrolled arrhythmias
• Recent pneumonectomy or single‑lung physiology
• Raised ICP or inability to tolerate sedation

BAL METHOD

Segment selection

• Diffuse disease: Right middle lobe or lingula (provide highest yield returns)
• Focal disease: Segment corresponding to radiological abnormality

Pre‑procedure

• Optimise oxygenation: FiO₂ 1.0; consider temporary PEEP increase
• Assess stability: FiO₂ requirement, PEEP, vasopressors, arrhythmias
• Clarify goals: microbiology only vs microbiology + cytology
• Ideally sample before new antibiotics (but do not delay life‑saving therapy)

Sedation

• Deep sedation ± paralysis in mechanically ventilated patients

Insertion

• Via ETT adaptor (e.g. Bodai‑Y connector)
• Monitor airway pressures; consider pressure‑controlled ventilation

Wedge

• Advance into target subsegment until a gentle wedge is achieved
• Maintain wedge throughout instillation and aspiration

Instillation

• Instill 3 × 20–40 mL aliquots (typical total 100–120 mL)
• Some centres use up to 150 mL

Aspiration

• Use gentle, low‑pressure suction to avoid airway collapse
• Manual syringe aspiration may improve return if suction poor

Sample handling

• First aliquot: use for cytology (best cellular morphology)
• Pooled aliquots: use for microbiology
• Request: Gram stain, culture, fungal, mycobacterial, viral PCR, cytology, special stains

NON‑DIRECTED BAL (ND‑BAL)

Method

• Confirm ETT tip is correctly placed in trachea (not a mainstem bronchus)
• Insert catheter through ETT (e.g. 50-60cm catheter)
• Advance catheter until resistance, then withdraw slightly
• Instill 20–60 mL total in aliquots
• Aspirate with syringe or suction while maintaining seal
• Label sample clearly as ND‑BAL

Advantages

• Rapid, bedside, low‑resource
• Can be performed by ICU staff without bronchoscopy
• Facilitates early sampling and stewardship

Limitations

• Non‑segmental; variable sample quality
• No airway visualisation
• Lower diagnostic precision than bronchoscopic BAL

ND‑BAL quality improvement data (Lewis et al, 2026):

• Earlier sampling after pneumonia suspicion
• lower oral flora contamination (50%) compared with ETA (90.9%), improving sample quality
• Safe, low complication rates
• Supports antimicrobial de‑escalation/escalation

COMPLICATIONS

• Hypoxaemia
  • transient minor hypoxaemia is common; mitigate with FiO₂ 1.0 and minimising duration
• Haemodynamic instability
  • rarely severe; often related to sedation, vagal stimulation, or underlying cardiovascular disease
• Bronchospasm
  • consider pre‑emptive bronchodilators
• Bleeding
  • usually minor; major bleeding rare
• Ventilator interactions
  • transient high airway pressures, auto‑PEEP during wedging

DIAGNOSTIC PERFORMANCE

Culture thresholds

• Quantitative cut‑offs: 10⁴–10⁵ CFU/mL (centre‑dependent)
• Interpret in context: organism identity, radiology, gas exchange, clinical trajectory

Microbiology

• Common organisms: Gram‑negative bacilli, S. aureus, fungi, viruses
• BAL provides current local epidemiology for ventilated patients
• Integrate results into antibiotic stewardship

Cytology

• Alveolar haemorrhage: progressively bloodier aliquots; ≥20% haemosiderin‑laden macrophages
• Eosinophilic pneumonia: BAL eosinophils >25%
• Malignancy: limited sensitivity; useful in bronchioloalveolar carcinoma, lymphangitis carcinomatosis, diffuse metastases
• Pulmonary alveolar proteinosis: milky, proteinaceous BAL with PAS‑positive debris

Interpretation pitfalls

• Candida, Enterococcus, coagulase‑negative staph are often colonisers
• Viral PCR positivity disease; interpret clinically
• BAL neutrophilia is non‑specific
• Mixed growth may reflect colonisation rather than infection
• BAL must be interpreted alongside radiology and clinical trajectory

Approximate diagnostic yields for different diagnoses

Diagnosis / Indication	Typical BAL Yield	Key Diagnostic Features
VAP / severe HAP	40–70%	Quantitative culture ≥10⁴–10⁵ CFU/mL; lower contamination than ETT aspirate
Atypical / non‑resolving pneumonia	40–70%	Fungal, viral, mycobacterial, Pneumocystis, Nocardia
Immunocompromised host infections	60–80%	High yield for PCP, CMV, fungi, Nocardia, mycobacteria
Alveolar haemorrhage	>90%	Progressively bloodier aliquots; ≥20% haemosiderin‑laden macrophages
Eosinophilic pneumonia	>90%	BAL eosinophils >25%
Pulmonary alveolar proteinosis	>90%	Milky BAL; PAS‑positive lipoproteinaceous debris
Interstitial lung disease patterning	60–80%	Lymphocytosis (HP/sarcoid), neutrophilia (infection/ARDS), eosinophilia (>25%)
Malignancy	20–40%	Best for bronchioloalveolar carcinoma, lymphangitis carcinomatosis
ND‑BAL for VAP	30–50%	Lower contamination than ETT aspirate; early sampling improves yield
Endotracheal aspirate (comparison)	20–40%	High contamination; poor stewardship value

BAL VS ENDOTRACHEAL ASPIRATE

Feature	Endotracheal aspirate	BAL / ND‑BAL
Contamination	High	Lower
Ease	Very easy	Moderate
Resource use	Minimal	Higher
Diagnostic accuracy	Lower	Higher
Stewardship value	Limited	Strong
Airway visualisation	None	complete (BAL, not ND-BAL)
Alveolar haemorrhage diagnosis	Poor	Strong

RELATED TECHNIQUES

Bronchial washings

• Proximal/segmental sampling; bronchoscope held just proximal to abnormality
• Instill 10–20 mL aliquots
• Yield ~50% (21–76%)
• Best for visible mucosal disease

Bronchial brushings

• Cytology brush advanced through working channel; scrape abnormal mucosa
• Yield ~59% (23–93%)
• Complications: minor bleeding; rare pneumothorax if blindly advanced

VIDEOS

ATS video demonstrating and discussing BAL procedure:

Bronchoscopy Academy video on BAL Fundamentals:

CONCLUSION

BAL is a useful diagnostic tool in critical care.

• While ND‑BAL is emerging as a pragmatic option for suspected VAP, bronchoscopic BAL remains essential for focal pathology, haemorrhage, and complex diagnostic dilemmas.
• BAL/ND‑BAL into ICU pneumonia assessment improves diagnostic accuracy and antiobitic stewardship.
• Risk-benefit balance should be considered before performing BAL

REFERENCES AND LINKS

Journal articles

• Anan K, Oshima Y, Ogura T, Tanabe Y, Higashi A, Iwashita Y, Fujita K, Yoshida T, Ando K, Okamori S, Okada Y. Safety and harms of bronchoalveolar lavage for acute respiratory failure: A systematic review and meta-analysis. Respir Investig. 2022 Jan;60(1):68-81. doi: 10.1016/j.resinv.2021.07.008. Epub 2021 Sep 4. PMID: 34489205.
• Azoulay E, Russell L, Van de Louw A, Metaxa V, Bauer P, Povoa P, Montero JG, Loeches IM, Mehta S, Puxty K, Schellongowski P, Rello J, Mokart D, Lemiale V, Mirouse A; Nine-i Investigators. Diagnosis of severe respiratory infections in immunocompromised patients. Intensive Care Med. 2020 Feb;46(2):298-314. doi: 10.1007/s00134-019-05906-5. Epub 2020 Feb 7. PMID: 32034433; PMCID: PMC7080052.
• British Thoracic Society Bronchoscopy Guidelines Committee, a Subcommittee of Standards of Care Committee of British Thoracic Society. British Thoracic Society guidelines on diagnostic flexible bronchoscopy. Thorax. 2001 Mar;56 Suppl 1(Suppl 1):i1-21. doi: 10.1136/thorax.56.suppl_1.i1. PMID: 11158709; PMCID: PMC1765978.
• Davidson KR, Ha DM, Schwarz MI, Chan ED. Bronchoalveolar lavage as a diagnostic procedure: a review of known cellular and molecular findings in various lung diseases. J Thorac Dis. 2020 Sep;12(9):4991-5019. doi: 10.21037/jtd-20-651. PMID: 33145073; PMCID: PMC7578496.
• Lewis G, Smith CD, Sundararajan K. Non-directed bronchoalveolar lavage: improving the quality and timing of pneumonia diagnosis in mechanically ventilated patients in the intensive care unit. BMJ Open Quality. 2026;15:e003787. https://doi.org/10.1136/bmjoq-2025-003787
• Martin WR, Padrid PA, Cross CE. Bronchoalveolar lavage. Clin Rev Allergy. 1990 Summer-Fall;8(2-3):305-32. doi: 10.1007/BF02914451. PMID: 2292101; PMCID: PMC7101538.
• McCarthy C, Bonella F, O’Callaghan M, Dupin C, Alfaro T, Fally M, Borie R, Campo I, Cottin V, Fabre A, Griese M, Hadchouel A, Jouneau S, Kokosi M, Manali E, Prosch H, Trapnell BC, Veltkamp M, Wang T, Toews I, Mathioudakis AG, Bendstrup E. European Respiratory Society guidelines for the diagnosis and management of pulmonary alveolar proteinosis. Eur Respir J. 2024 Nov 14;64(5):2400725. doi: 10.1183/13993003.00725-2024. PMID: 39147411.