Bronchoscopy-derived correlates of lung injury following inhalational injuries: a prospective observational study

Abstract

Background: Acute lung injury (ALI) is a major factor determining morbidity following burns and inhalational injury. In experimental models, factors potentially contributing to ALI risk include inhalation of toxins directly causing cell damage; inflammation; and infection. However, few studies have been done in humans.

Methods: We carried out a prospective observational study of patients admitted to the NC Jaycees Burn Center who were intubated and on mechanical ventilation for burns and suspected inhalational injury. Subjects were enrolled over an 8-month period and followed till discharge or death. Serial bronchial washings from clinically-indicated bronchoscopies were collected and analyzed for markers of cell injury and inflammation. These markers were compared with clinical markers of ALI.

Results: Forty-three consecutive patients were studied, with a spectrum of burn and inhalation injury severity. Visible soot at initial bronchoscopy and gram negative bacteria in the lower respiratory tract were associated with ALI in univariate analyses. Subsequent multivariate analysis also controlled for % body surface area burns, infection, and inhalation severity. Elevated IL-10 and reduced IL-12p70 in bronchial washings were statistically significantly associated with ALI.

Conclusions: Independently of several factors including initial inhalational injury severity, infection, and extent of surface burns, high early levels of IL-10 and low levels of IL-12p70 in the central airways are associated with ALI in patients intubated after acute burn/inhalation injury. Lower airway secretions can be collected serially in critically ill burn/inhalation injury patients and may yield important clues to specific pathophysiologic pathways.

Figure 1. Comparison of airway injury score (graded for soot, inflammation, epithelial sloughing and secretions at <72 hr post injury), between patients with the lowest PaO₂/FiO₂ ratios during the first 2 weeks post injury (PaO₂/FiO₂) of <200 (N = 16), and patients with PaO₂/FiO₂ ≥200 (N = 24).

Bars represent mean ± SE. P = 0.11, t-test with Welch's correction for unequal variances.

Figure 2. Comparison of the lowest PaO₂/FiO₂ ratios during the first 2 weeks post injury (PaO₂/FiO₂) among patients with no bacterial pathogens isolated from respiratory secretions during the first 2 weeks (NEG), patients with bacterial pathogens of any type (POS), and patients with gram negative bacteria (GN POS).

Patients in whom no bacterial cultures were collected are not included in this analysis. * = P<.05 vs. NEG.

Figure 3. Comparison of averaged early (<72 hr post injury) IL-10 concentrations in mainstem bronchial washings, between the lowest PaO₂/FiO₂ ratios ratios during the first 2 weeks post injury (PaO₂/FiO₂) of <200 (N = 16), and patients with PaO₂/FiO₂ ≥200 (N = 24).

Bars represent mean ± SE. * P<0.05, t-test with Welch's correction for unequal variances.

Figure 4. Comparison of averaged early (<72 hr post injury) IL-12p70 concentrations in mainstem bronchial washings, between the lowest PaO₂/FiO₂ ratios during the first 2 weeks post injury (PaO₂/FiO₂) of <200 (N = 16), and patients with PaO₂/FiO₂ ≥200 (N = 24).

Bars represent mean ± SE.

Figure 5. Comparison of IL-10 to IL-12p70 ratios in mainstem bronchial washings, between patients with the lowest PaO₂/FiO₂ ratios during the first 2 weeks post injury (PaO₂/FiO₂) of <200 (N = 16), and patients with PaO₂/FiO₂ ≥200 (N = 24).

Bars represent mean ± SE. * P<0.05, t-test with Welch's correction for unequal variances.