Respiratory Mechanical Unloading Decreases Thoraco-Abdominal Asynchrony and Chest Wall Distortion In Very Low Birth Weight Preterm Infants. † 1552

Thoraco-abdominal asynchrony (TAA) and chest wall distortion (CWD) occur frequently in preterm infants decreasing the efficiency of the respiratory pump. We hypothesized that respiratory mechanical unloading with proportional assist ventilation (PAV) would reduce TAA and CWD in preterm infants. We determined TAA and CWD in 10 preterm infants (mean BW= 837±195, median age 2.5 days) using calibrated respiratory inductive plethysmography. TAA was expressed as the phase angle between the rib cage and abdominal motion and CWD as the total compartmental displacement/VT ratio (TCD/VT, increases over 1.0 when there is distortion). In addition we measured tidal volume(Vt) with a pneumotachograph and esophageal (δPes) and airway pressure deflections with pressure transducers. These values were used to calculate the end inspiratory transpulmonary pressure (Tpp). Measurements were obtained during alternating periods of CPAP and PAV using two different degrees of unloading(GAIN 1= 1.09±0.68, GAIN 2=1.84±0.84 cmH₂O/ml). PAV decreased TAA and CWD in comparison to CPAP and this was dependent on the degree of unloading. (Table: mean and SD, Repeated Measures ANOVA, *=p<0.05 compared to CPAP, ♦=p<0.05 compared to GAIN 1. δPes, Tpp:cmH₂O, Vt:ml/kg)

Table 1

We conclude that PAV improves thoraco-abdominal synchrony and decreases chest wall distortion in VLBW infants contributing to larger tidal volumes with less negative deflection in esophageal pressure.