To evaluate surfactant content and function through the lamellar body count (LBC) and stable microbubble test (SMT) in mechanically ventilated infants with severe acute viral bronchiolitis.

Controlled cross-sectional study of 32 infants receiving mechanical ventilation: 16 with a diagnosis of acute viral bronchiolitis and 16 with normal lungs. Tracheal fluid was collected and LBC was performed in an automated cell counter. Samples were kept frozen and thawed for testing. At the time of analysis, samples were diluted in a dithiothreitol solution, vortexed for 10 seconds, and aspirated by the cell counter. SMT was performed using the Pattle technique.

In the bronchiolitis group, the median (IQR) LBC was significantly lower than in the control group: 130 000 (61 250-362 250) vs 518 000 (180 250-896 000) lamellar bodies/μL; P = .003. Median (IQR) SMT values were also significantly lower in the bronchiolitis group: 10 (2-13) vs 400 (261-615) microbubbles/mm²; P < .001.

Infants with acute viral bronchiolitis have reduced surfactant content and function. We speculate that these simple tests may be useful to identify infants with bronchiolitis who would benefit from surfactant replacement therapy.