204 Maturation of Lung Function During The First Two Years of Life in Infants with Congenital Diaphragmatic Hernia (CDH) Treated with a Gentle Ventilation and Delayed Surgery Strategy

Abstract

Background: CDH is still characterized by high morbidity and mortality, mostly due to lung hypoplasia. Recently, gentle ventilation and delayed surgery have been suggested to improve mortality and long-term pulmonary sequelae. The assessment of lung volumes, particularly functional residual capacity (FRC), is crucial for understanding lung development during the first year of life. The sulphur hexafluoride (SF6) wash-in / wash-out technique together with an ultrasonic flow meter, can measure both FRC and lung clearance index (LCI), a very sensitive and stable index of ventilation homogeneity. Aim: To evaluate changes in lung function during the first two years of life in infants with CDH requiring mechanical ventilation and surgically corrected in the neonatal period. Methods: Ten CDH infants (means±SD: BW=3082±570 g and GA=39.1±1.7 wks, M/F=8/2, Left/Right CDH 8/2) surgically corrected in the neonatal period were studied twice during the first two years of life, with at least six months interval between measurements. Tidal Volume (Vt), Respiratory Rate (RR) and time to peak expiratory flow/expiratory time ratio (tPTEF/Te, an index of lower airways patency) were measured with an ultrasonic flow meter; Compliance (Crs) and Resistance (Rrs) of the respiratory system were studied with the single occlusion technique; FRC and LCI were assessed with the multiple breath SF6 wash-in/wash-out technique. The differences between the first and second measurement were considered statistically significant for p <0.05 by the Student's t-test for paired values. Results: All 10 infants were studied at 5.0±2.7 (T1) and 12.8±4.2 (T2) months of age. At T1: Vt (7.9±2.1 ml/kg), RR (47.8±14.0 b/m'), Crs (2.1±0.4 ml/cmH2O/kg) were within normal limits; tPTEF/Te (0.18±0.05) and FRC (19.2±4.2 ml/kg) were slightly lower, while Rrs (52.2 ± 19.2 cmH2O/l/s) and LCI (10.8±2.5; normal values <7.1) were higher than normal. At T2: Vt (9.7±1.8 ml/kg) and RR (32.5±6.4 b/m') improved significantly (p<0.05 and p<0.01), while Crs (2.2±0.6 ml/cmH2O/kg), Rrs (53.0±25.8 cmH2O/l/s), tPTEF/Te (0.17±0.05), FRC (21.6±3.4 ml/kg) and LCI (11.2±2.5) did not change appreciably when compared with T1. Conclusions: Lung function in infants with severe CDH is characterized by a persistent impairment of lung volumes and ventilation inhomogeneity, despite an improvement in Vt and RR and normal values of Crs, during the first two years of life. These results can explain in part the higher respiratory morbidity in these patients.