Distribution of tidal ventilation during volume-targeted ventilation is variable and influenced by age in the preterm lung.

PURPOSE: Synchronised volume-targeted ventilation (SIPPV + VTV) attempts to reduce lung injury by standardising volume delivery to the preterm lung. The aim of this study is to describe the regional distribution and variability of ventilation within the preterm lung during SIPPV + VTV.
METHODS: Twenty-seven stable, supine, preterm infants with <32 weeks gestation receiving SIPPV + VTV were studied. From each infant, the anterior-to-posterior impedance change due to tidal ventilation (∆Z (VT); countless units) was determined during every breath from three, 30-s, electrical impedance tomography recordings. ∆Z (VT) within the anterior, middle and posterior thirds of the chest were compared using area under the curve analysis. The coefficient of variation (CV) of ∆Z (VT) in the anterior and posterior hemithoraces, inflation pressure and, where available, V (T) at airway opening were compared. Infants were sub-grouped by age (≤7 and >7 days), supplemental oxygen requirement and set tidal volume.
RESULTS: In all sub-groups, the middle third of the chest accounted for the greatest ∆Z (VT) [p < 0.0001, repeated-measures analysis of variance (ANOVA)]. The middle third of the chest constituted a greater relative ∆Z (VT) in infants aged >7 days compared with ≤7 days (p < 0.0001, repeated-measures ANOVA). Set tidal volume and oxygen requirement did not significantly influence the regional distribution of ∆Z (VT). The mean (standard deviation, SD) CV of ∆Z (VTANT) and ∆Z (VTPOST) were 30.6% (14.0%) and 31.9% (12.7%). ∆Z (VTANT) and ∆Z (VTPOST) expressed greater breath-to-breath variability than the variation in inflation pressure and V (T) at airway opening (p = 0.012 and p < 0.0001, respectively, paired t-tests).
CONCLUSION: During SIPPV + VTV the preterm infant exhibits marked breath-to-breath variability in regional ventilation which is influenced by age.