Evolution of respiratory mechanics in preterm babies after surfactant administration in the neonatal period.

Objective: To evaluate the development of the lung of preterm infants given exogenous surfactant in the neonatal period versus control babies through the evolution of respiratory mechanics (RM) parameters.

Patients and methods: Retrospective analysis of babies < or = 30 weeks' gestation admitted to our intensive care unit in the period 1990-94 in which RM parameters had been followed for the first two years of life. Babies were divided into two groups depending on the fact that they received endotracheal porcine surfactant 200 mg/kg for prophylaxis or rescue treatment of respiratory distress syndrome (RDS) (treatment group, No.37) or not (control group, No.41). Evaluation of RM were performed by means of PèDS at the post-conceptual age of 38-42 wks and/or 3-6 mth and/or 9-12 mth and/or 18-24 mth in spontaneous breathing after sedation with chloral hydrate and positioning of an oesophageal balloon. Chronic lung disease (CLD) was defined a posteriori as presence of polypnea at discharge independently from oxygen-therapy and from radiological findings, including also the most severe forms of bronchopulmonary dysplasia.

Results: The treatment and control group did not differ for birth weight and gestational age (1060 +/- 293 vs 1189 +/- 321 g. and 28.1 vs 28.3 +/- 1.5 wks respectively), however the babies of the treatment group had higher incidence of RDS, mechanical ventilation, nasal continuous positive airway pressure, and use of caffeine (p < 0.01 vs the control group). No difference was found in the incidence of CLD at discharge between the two groups. No difference was found between the treatment and the control group at the various times of the examinations concerning respiratory frequency, tidal volume, minute ventilation, dynamic compliance of the respiratory system (indexed both to body weight and length), and respiratory system resistances. The above cited parameters, except respiratory system resistances, showed significant changes from the first to the last evaluation (p < 0.01) in both groups, indicating a continuous improvement of the RM properties of the lung in the first two years of life. As regards respiratory system resistances, these were significantly reduced in the first two years of life in the treatment group (from 73.9 +/- 38.5 to 31.3 +/- 5.8 cmH2O/L/sec; p < 0.05), while there was no significant improvement in the control group (from 65.1 +/- 26.1 to 42.8 +/- 41.6 cmH2O/L/sec; p = ns).

Conclusion: The use of surfactant both as prophylactic and rescue treatment of RDS seems able to guarantee the lung of the preterm infant to develop in a regular way, in spite of high incidence of respiratory diseases and unfavourable effects of respiratory therapies. This study also allows to have standard reference values of RM parameters for ex-preterm infants in the first two years of life to evaluate their lung development.