Lung function in the supine and lateral decubitus positions in anaesthetized infants and children.

We have measured dynamic lung compliance or static lung thorax compliance, functional residual capacity (FRC), and two indices of pulmonary gas mixing (pulmonary clearance delay (PCD) and single breath alveolar mixing efficiency (SBAME)) in 25 children in the supine and lateral decubitus position during nitrous oxide-halothane anaesthesia. Fifteen children (5 month-8 yr) breathed spontaneously and 10 (4 month-9 yr) underwent mechanical ventilation. Tidal volume and rate of ventilation were, respectively, 3.5-6.6 ml kg-1 and 22-46 b.p.m. in spontaneously breathing supine children, and 8.3-15 ml kg-1 and 20-30 b.p.m. in mechanically ventilated supine children, and did not differ significantly in the lateral position. There was no significant change in compliance when the child was turned to the lateral position, but FRC increased from 22 (SD7) to 25 (8) ml kg-1 (P less than 0.01) in the spontaneously breathing group and from 19 (6) to 24 (8) ml kg-1 (P less than 0.01) in the other group. In spontaneously breathing children, PCD and SBAME indicated a somewhat impaired pulmonary gas mixing (P less than 0.05) after the child had been turned to the lateral position, but no change occurred in the other group. These findings suggest that the distribution of ventilation in anaesthetized children in the lateral position is similar to that reported previously in anaesthetized adults.