A new method of ventilation inhomogeneity assessment based on a simulation study using clinical data on congenital diaphragmatic hernia cases

Congenital Diaphragmatic Hernia (CDH) is a diaphragm defect associated with lung hypoplasia and ventilation inhomogeneity (VI). The affected neonates are usually born with respiratory failure and require mechanical ventilation after birth. However, significant interindividual VI differences make ventilation difficult. So far, there are no clinical methods of VI assessment that could be applied to optimize ventilation at the bedside. A new VI index is a ratio of time constants T(1)/T(2) of gas flows in both lungs. Pressure-controlled ventilation simulations were conducted using an infant hybrid (numerical-physical) respiratory simulator connected to a ventilator. The parameters of the respiratory system model and ventilator settings were based on retrospective clinical data taken from three neonates (2, 2.6, 3.6 kg) treated in the Paediatric Teaching Clinical Hospital of the Medical University of Warsaw. We searched for relationships between respiratory system impedance (Z) and ventilation parameters: work of breathing (WOB), peak inspiratory pressure (PIP), and mean airway pressure (MAP). The study showed the increased VI described by the T(1)/T(2) index value highly correlated with elevated Z, WOB, PIP and MAP (0.8–0.9, the Spearman correlation coefficients were significant at P < 0.001). It indicates that the T(1)/T(2) index may help to improve the ventilation therapy of CDH neonates.