Postnatal changes in pulmonary mechanics and energetics of infants with respiratory distress syndrome following surfactant treatment.
BACKGROUND
Postnatal alterations in pulmonary mechanics, energetics and functional residual capacity (FRC) describe the structural maturation of the preterm respiratory system.


OBJECTIVE
To evaluate longitudinal changes in pulmonary function in infants with respiratory distress syndrome (RDS) treated with oxygen, positive pressure ventilation and synthetic surfactant (Exosurf).


METHODS
Serial pulmonary function tests were performed in surfactant-treated infants [mean +/- SD birth weight (BW) = 1,112 +/- 276 g, gestational age (GA) = 29 +/- 3 weeks] at postnatal ages: <3 days, 1, 2, 3, 4 and 6-8 weeks until term postmenstrual age (PMA). Tidal volume, pulmonary compliance (C(L)), pulmonary resistance (R(T)) and flow-resistive work were analyzed following simultaneous measurements of airflow and transpulmonary pressure signals. Serial FRC measurements were made in a randomly selected group.


RESULTS
Prior to 28 weeks' PMA, C(L) was unchanged irrespective of GA. At age 1 week the likelihood ratio (LR) for bronchopulmonary dysplasia (BPD) based on C(L), R(T) and GA was predicted to be >90% for those with BW <750 g (LR >100) as compared to <10% probability (LR = 0.3) for infants >1,500 g. Significant linear increase in C(L) to PMA was evident >28 weeks' PMA (r = 0.86, p < 0.01) at 0.17 ml/cm H2O/kg/week. By term PMA, mean C(L) was 2.60 +/- 0.07 ml/cm H2O. Improvements in FRC of preterm infants with RDS who recovered occur at a more rapid rate ( approximately 25 ml/kg) compared to those who developed BPD ( approximately 20 ml/kg).


CONCLUSIONS
Slow but incremental postnatal pulmonary improvement, minimal <28 weeks' PMA, were comparable for all infants. Along with diminished FRC, these changes reflect persistent deleterious effects of positive pressure ventilation, alveolar hyperoxia and unrecognized pulmonary overdistension.
Department of Pediatrics, Division of Neonatal and Developmental Medicine, Stanford University School of Medicine, Stanford, CA 94305-5731, USA. bhutani@stanford.edu
Vinod K
VK
Bhutani
Frank W
FW
Bowen
Emidio M
EM
Sivieri
D045422:Continuous Positive Airway Pressure; D004338:Drug Combinations; D005233:Fatty Alcohols / Q000008:administration & dosage / Q000627:therapeutic use*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D008137:Longitudinal Studies; D010100:Oxygen / Q000008:administration & dosage; D010767:Phosphorylcholine / Q000008:administration & dosage / Q000627:therapeutic use*; D011092:Polyethylene Glycols / Q000008:administration & dosage / Q000627:therapeutic use*; D011663:Pulmonary Surfactants / Q000008:administration & dosage / Q000627:therapeutic use*; D012127:Respiratory Distress Syndrome, Newborn / Q000188:drug therapy* / Q000503:physiopathology*; D012129:Respiratory Function Tests; D012189:Retrospective Studies
D004338:Drug Combinations; D005233:Fatty Alcohols; D011663:Pulmonary Surfactants; D010767:Phosphorylcholine; D011092:Polyethylene Glycols; C047049:dipalmitoylphosphatidylcholine, hexadecanol, tyloxapol drug combination; D010100:Oxygen