Partial forced expiratory flow-volume curves in young children during ketamine anesthesia

Maximal flows at functional residual capacity (V̇max(FRC)) from partial forced expiratory flow-volume (PEFV) curves were obtained in 14 normal preschool children (8 boys, 6 girls) of average age 44 mo, under general anesthesia before elective surgery. PEFV curves were generated from end inspiration by rapid compression of the chest wall with an inflatable jacket. V̇max(FRC), expressed in milliliter per second, correlated linearly with height, weight, age, and FRC in millileter and milliliters per kilogram. The best correlation of V̇max(FRC) (ml/s) was to height to the power of 2.47, which agrees with the results predicted by wave-speed theory. Mean FRC-corrected V̇max(FRC) was 2.42 ± 0.50 (SD) FRC's/s with no significant difference between boys (2.35 FRC's/s) and girls (2.51 FRC's/s). There was no correlation between lung-size corrected V̇max(FRC) and height, weight, or age, but it tended to decrease with increasing FRC. The intersubject variability for V̇max(FRC) was reduced by normalizing for FRC, and was significantly better than that reported for awake children. This can be attributed to the greater control over volume history and more reliable maximal flow generation during anesthesia. The intrasubject coeffient of variation (CV) for V̇max(FRC) was 12.2%, and the intersubject CV was 20.0%. The difference may represent the variability due to dysanapsis. It is concluded that dysanapsis is not a prominent factor in children of this age group. In addition, the similarity of the regression equation for V̇max(FRC) vs. height to that of FRC vs. height supports the concept of equidimensional growth of the airways and lung parenchyma.