Abstract 1886

Purpose: Airway colonization with various organisms is common in mechanically ventilated neonates. However, differentiation between colonization and possible infection is difficult and often made on clinical grounds. We examined the relationship between IL-6 and TNF-α concentrations in BAL, their association with isolation of organisms and the effect of systemic steroids.

Methods: We prospectively obtained BAL in intubated newborns [n=15, 26-38 weeks gestation; postnatal ages 1-90d]. Twice-weekly samples were analyzed for white cell count, epithelial cells, isolation of organisms, IL-6, TNF-α and free-secretory piece of IgA [secIgA].

Results: Of the 40 samples, 62% had either gram positive [+ve](25%) or gram negative [-ve](37%) organisms; 5% had multiple organisms. Isolated organisms: Staph, epidermidis (22%), Enterobacter cloacae (25%), Acinobacter (7.5%) and Serratia (5%). IL-6 and TNF-α concentrations varied from 0.22 to 10.72 and 0.025 to 61.02 ng/mg secIgA, respectively. Medium values for IL-6/secIgA: 1.46(25-75%ile:1.17-2.24) no organisms, 2.45 (25-75%ile:1.15-3.39) +ve organisms and 2.02 (25-75%ile:1.35-4.13) -ve organisms [p=0.465 by Kruskal Wallis one way ANOVA on ranks]. Median values for TNF-α/secIgA:4.00 (3.09-12.5) no organisms, 4.95 (2.6-13.4) +ve organisms and 6.04 (2.70-21.10) -ve organisms [p=0.746]. There was a significant relationship between BAL TNF-α and IL-6 [p<0.001, r=0.61]. In the absence of organisms, systemic steroids did not significantly alter the cytokine concentrations; however, in the presence of organisms and systemic steroids, IL-6 increased significantly [p=0.032]. Cytokine concentrations did not change with postnatal age; duration of intubation correlated significantly with isolation of organisms [p<0.001].

Conclusions: There is a strong linear relationship between BAL IL-6 and TNF-α. Cytokine concentrations did not appear to be influenced by the presence or absence of BAL organisms suggesting airway colonization rather than infection. Further, isolation of organisms was more likely with increased duration of intubation. These data suggest that single, random values of IL-6 and TNF-α may not differentiate infection from colonization, rather sequential studies are needed to make the clinical differentiation unless the concentration are markedly increased. IL-6, the pro-inflammatory Cytokine increases with the use of systemic steroids.

Clinical Implications: Isolation of organisms in BAL, even gram -ve organisms, may not indicate infection.