Passive total respiratory system compliance and gas exchange in newborns with hyaline membrane disease

Passive total respiratory system compliance (CRS) and gas exchange measurements were performed in nine newborns during the course of hyaline membrane disease. None of the subjects presented bronchopulmonary dysplasia at follow-up investigations. Gestational age ranged from 29 to 37 weeks. CRS was measured by the multiple occlusion technique. Gas exchange parameters were the fraction of inspired oxygen concentration (FIO2) and the arterial/alveolar ratio for oxygen (a/AO2 ratio). In each subject four tests were performed: test 1 during the first day of life; test 2 during the second day of life; test 3 between the fourth and the seventh days of life; test 4 after extubation. CRS/BW (CRS normalized for body weight) was not statistically different at tests 1-3, but it significantly increased (P less than 0.001) between tests 3 and 4. FIO2 and a/AO2 ratio presented no statistical difference at tests 1-2 but several significant differences were noted thereafter: FIO2 decreased significantly (P less than 0.001) when results from tests 2 and 3 were tabulated. The a/AO2 ratio increased significantly between tests 2 and 3 (P less than 0.001), and a further significant increase (P less than 0.01) was also noted when results obtained during tests 3 and 4 were compared. A significant relationship existed during the evolution of the disease between CRS/BW and gas exchange parameters (FIO2 and a/AO2 ratio) (P less than 0.01), but gas exchange improved earlier than lung mechanics.