Prone equals prone? – impact of different techniques of body positioning on functional residual capacity and ventilation distribution in anaesthetised, paralysed preschool children

Introduction: In children undergoing anesthesia or sedation, optimizing functional residual capacity (FRC) is of special importance, because they have smaller elastic retraction forces compared with adults and a lower relaxation volume that makes them more prone to airway collapse. Moreover, children are particularly vulnerable to hypoxaemia because of their higher oxygen demand per kilo body weight. Although the prone position is effectively used to improve oxygenation, its impact on FRC is controversial. Thus, additional confounding factors such as changes in ventilation distribution or differences in positioning techniques might be of importance. In fact, positioning techniques such as flat versus augmented prone position could exert different degrees of pressure on the abdominal contents and thus differences in the cephalic displacement of the diaphragm. The aim of this study was to determine the impact of two different prone positioning techniques on FRC and ventilation distribution in anesthetized, paralyzed preschool‐aged children. We hypothesized that augmented prone positioning improves FRC and ventilation distribution compared with the supine or flat prone position. Methods: Following local Ethics Committee approval, 30 preschool children without cardiopulmonary disease undergoing elective surgery were studied. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF6) multibreath washout technique. After intubation, the measurements were taken in the supine position and in random order in the flat prone and augmented prone position (gel pads supporting the pelvis and the upper thorax to ensure free movement of the abdomen). The position of the arms was kept constant and the head was turned to the side for all assessments. Measurements were taken 5 min after each positioning. Results: Mean (range) age was 48.5 (24–80) months, weight = 17.2 (10.5–26.9) kg. FRC (mean ± SD) was 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 LCI was 8.1 ± 2.3 vs 7.9 ± 2.3 in these two positions, respectively. In contrast, FRC increased to 27.6 ± 6.5 ml·kg‐1 (P < 0.001) in the augmented prone position while at the same time the LCI decreased to 6.7 ± 0.9 (P < 0.001). Conclusions: FRC 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 could have a major impact on respiratory function in anaesthetized, mechanically ventilated preschool children. Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland.