Objectives: Although the prone position is effectively used to improve oxygenation, its impact on functional residual capacity is controversial. Different techniques of body positioning might be an important confounding factor. The aim of this study was to determine the impact of two different prone positioning techniques on functional residual capacity and ventilation distribution in anesthetized, preschool-aged children. Design: Functional residual capacity and lung clearance index, ameasure of ventilation homogeneity, were calculated using asulfur-hexafluoride multibreath washout technique. After intubation, measurements were taken in the supine position and, in random order, in the flat prone position and the augmented prone position (gel pads supporting the pelvis and the upper thorax). Setting: Pediatric anesthesia unit of university hospital. Patients and participants: Thirty preschool children without cardiopulmonary disease undergoing elective surgery. Measurements and results: Mean (range) age was 48.5 (24-80) months, weight 17.2 (10.5-26.9) kg, functional residual capacity (mean ± SD) 22.9 ± 6.2 ml.kg−1 in the supine position and 23.3 ± 5.6 ml.kg−1 in the flat prone position, while lung clearance indices were 8.1 ± 2.3 vs. 7.9 ± 2.3, respectively. In contrast, functional residual capacity increased to 27.6 ± 6.5 ml.kg−1 (p< 0.001) in the augmented prone position while at the same time the lung clearance index decreased to 6.7 ± 0.9 (p< 0.001). Conclusions: Functional residual capacity and ventilation distribution were similar in the supine and flat prone positions, while these parameters improved significantly in the augmented prone position, suggesting that the technique of prone positioning has major implications for pulmonary functio
