Bronchoscopy in inhalation injury

Overview

Fiberoptic bronchoscopy (FOB) is regarded as the current standard for diagnosing and grading subglottic inhalation injury in burn patients ^[1][3]. It provides direct visualization of the tracheobronchial mucosa, allowing assessment of edema, erythema, carbonaceous deposits, mucosal necrosis, and cast formation. Beyond diagnosis, bronchoscopy serves therapeutic purposes including removal of casts, secretion clearance, and guided lavage ^[1][9].

Despite its widespread use, the predictive value of bronchoscopic grading for clinical outcomes such as mortality, ventilator days, and pneumonia remains debated ^[4][5][7].

Grading Systems

Multiple grading systems exist for bronchoscopic assessment of inhalation injury. No single system has achieved global consensus ^[1][3].

Abbreviated Injury Score (AIS)

The most commonly used grading system, classifying injury from grade 0 (no injury) to grade 4 (massive injury) based on mucosal findings:

• Grade 0: No injury. Normal-appearing mucosa.
• Grade 1: Mild. Minor erythema, carbonaceous deposits.
• Grade 2: Moderate. Moderate erythema, bronchorrhea, carbonaceous deposits with friability.
• Grade 3: Severe. Severe edema, friability, obliteration of bronchi by debris.
• Grade 4: Massive. Evidence of mucosal sloughing, necrosis, endoluminal obliteration.

Inhalation Injury Severity Score (I-ISS)

A prospective observational study of 99 intubated burn patients compared three grading systems and found that only the I-ISS was independently associated with overall survival on regression analysis (score 3 vs scores 1-2: OR 13.16, 95% CI 1.65-105.07, P = 0.02) ^[4]. The AIS and mucosal score were not independently associated with survival in this study ^[4].

Deep Learning Approaches

Emerging research has applied deep learning frameworks to bronchoscopic images for automated grading. A vision transformer model trained on 1,089 frames from 36 patients achieved 98.17% accuracy for severity grade identification, suggesting potential for more objective and reproducible grading ^[8].

Diagnostic Value

Bronchoscopic diagnosis of inhalation injury affects clinical decision-making, though its independent contribution to outcomes is complex ^[5][7].

A prospective study of 192 patients found that while inhalation injury diagnosed through history alone did not predict mortality, severe injury on bronchoscopy was an independent predictor of death (adjusted OR 45.357) ^[5]. Mechanical ventilation requirement was also independently associated with mortality (adjusted OR 9.787) ^[5].

However, a large propensity-matched analysis of 3,014 burn patients from the National Burn Repository found that patients who underwent diagnostic bronchoscopy on admission had significantly higher rates of pneumonia, mortality, longer hospitalization, and longer duration of mechanical ventilation compared to matched controls who did not undergo the procedure ^[7]. The authors cautioned that these findings reflect correlations and may indicate selection bias (sicker patients receiving bronchoscopy) rather than procedural harm, but raised questions about the routine use of diagnostic FOB ^[7].

Timing

The optimal timing for initial bronchoscopy is within 24 hours of injury ^[5][9]. Serial bronchoscopy may be valuable for tracking injury progression, as admission bronchoscopic grade may not capture the full extent of evolving mucosal injury ^[4]. In one series, G2-level injuries were re-examined at 24 hours and G1-level injuries at 72 hours, with repeat assessments every 2-3 days until recovery ^[9].

Therapeutic Bronchoscopy

Beyond diagnosis, bronchoscopy serves direct therapeutic roles in inhalation injury management ^[1][3]:

• Cast removal: Direct suctioning and mechanical debridement of fibrin and mucus casts that obstruct airways.
• Secretion clearance: Lavage and aspiration of carbonaceous material and inspissated secretions.
• Assessment of treatment response: Serial bronchoscopy can guide decisions about ongoing nebulized therapy and ventilator management.
• Confirmation of extubation readiness: Airway visualization before planned extubation to assess mucosal healing and airway caliber.

An evidence-based review found that bronchoscopy combined with suctioning for debris removal has supporting data, though no RCTs exist ^[6].

Role in Outcome Prediction

An international RAND/UCLA expert panel identified bronchoscopy as essential for inhalation injury diagnosis but noted significant limitations in its ability to predict outcomes using current grading systems ^[2]. The panel recommended development of more sophisticated assessment tools and considered imaging modalities such as chest CT as potentially complementary ^[2].

A retrospective cohort study of 830 critically injured burn patients found that inhalation injury (diagnosed clinically and confirmed by bronchoscopy in 62% of cases) was associated with increased in-hospital mortality (31% vs 6%, adjusted OR 2.35), pneumonia, and tracheostomy, but was not associated with postdischarge mortality or readmission ^[10].

Controversies and Evidence Gaps

• Whether routine diagnostic bronchoscopy improves outcomes compared to clinical assessment alone has not been demonstrated in a prospective trial ^[7].
• The optimal grading system remains undefined. Agreement between existing systems is strong (Krippendorff's alpha 0.85), but their prognostic value varies ^[4].
• The potential for bronchoscopy itself to cause harm (mucosal trauma, nosocomial infection from the procedure) in already-injured airways has not been rigorously studied ^[7].
• Serial bronchoscopy protocols vary widely between institutions. Standardized timing and indications for repeat assessment are lacking VERIFY.
• Integration of CT imaging and AI-based grading with bronchoscopic assessment is an active research area without established clinical protocols ^[2][8].

References

[1] Foncerrada G et al. "Inhalation Injury in the Burned Patient." Ann Plast Surg 2018;80(3 Suppl 2):S98-S105. PMID: 29461292. [2] Milton-Jones KJ et al. "An international RAND/UCLA expert panel to determine the optimal diagnosis and management of inhalation injury." Crit Care 2023;27:459. PMID: 38012797. [3] Walker PF et al. "Diagnosis and management of inhalation injury: an updated review." Crit Care 2015;19:351. PMID: 26507130. [4] Flinn AN et al. "Inhalation Injury Severity Score on Admission Predicts Overall Survival in Burn Patients." J Burn Care Res 2023;44(6):1273-1277. PMID: 37279511. [5] You K et al. "Inhalation injury in burn patients: establishing the link between diagnosis and prognosis." Burns 2014;40(8):1470-5. PMID: 25406889. [6] Deutsch CJ et al. "The diagnosis and management of inhalation injury: An evidence based approach." Burns 2018;44(5):1040-1051. PMID: 29398078. [7] Ziegler B et al. "Impact of diagnostic bronchoscopy in burned adults with suspected inhalation injury." Burns 2019;45(6):1275-1282. PMID: 31383606. [8] Zhang K, Singh S. "Deep learning framework for bronchoscopic diagnosis of burn inhalation injury." Burns 2025;52(1):107770. PMID: 41297238. [9] Bai C et al. "Application of flexible bronchoscopy in inhalation lung injury." Diagn Pathol 2013;8:174. PMID: 24144059. [10] Witt CE et al. "Inpatient and Postdischarge Outcomes Following Inhalation Injury Among Critically Injured Burn Patients." J Burn Care Res 2021;42(6):1168-1175. PMID: 33560337.