Repeatability of cellular constituents and cytokine concentration in fluidobtained by non-bronchoscopic bronchoalveolar lavage of infants receiving extracorporeal oxygenation

Background-Since few studies have assessed the repeatability of non-broncho scopic bronchoalveolar lavage (NB-BAL), we compared cellular counts and cyt okine concentrations in fluid obtained by standardised NB-BAL from each sid e of 20 intubated infants receiving extracorporeal membrane oxygenation (EC MO). Methods-Total cell counts were obtained from 95 paired lavages and 77 pairs were suitable for differential counts and measurement of cytokine concentr ations. Results-Moderate correlation was noted between the two sides for most cell types including total cell counts and percentages of neutrophils and macrop hages (R=0.700-0.84) and for cytokine concentrations (IL-8 R=0.78, IL-6 R=0 .75, TNF-alpha R=0.64, all p less than or equal to0.001). Using Bland-Altma n analysis the mean difference between the two sides approached zero for ce llular constituents (total cell counts mean difference 1.7, limits of agree ment -187.5 to +190.9 X 10(4)/ml; percentage neutrophils -3.9%, -41.5% to 33.6%; percentage macrophages 3.9%, -33.8% to +41.6%) but tended to be grea ter on the right for logarithmically transformed cytokine measurements (IL- 8: left/ right ratio 0.74, limits of agreement 0.12 to 5.45, IL-6: 0.93, 0. 09 to 5.87, and TNF-alpha: 0.93, 0.27 to 3.16). Using linear regression wit h random effects to assess the variability only the infant's age appeared t o influence the cellular results but, for cytokines, only the volume retrie ved affected the variability. The magnitude of the measurements, the underl ying disease, the operator's experience, days on ECMO, or survival did not affect the variability. Conclusion-Measurements obtained by NB-BAL need to be interpreted with caut ion and strongly suggest that normalisation for the dilutional effects of s aline is essential.