The study also raises the question of whether additional replacement surfactant treatment may benefit such infants, just as it does in the week after birth.
Neonatology researchers from The Children's Hospital of Philadelphia and the University of Pennsylvania published the study in the October 20 online edition of the journal Pediatric Research. It was the first study of surfactant dysfunction in infants beyond the first week of life.
"We studied premature babies who require mechanical ventilation to breathe after one week of age," said Philip L. Ballard, M.D., Ph.D., director of Neonatology Research at The Children's Hospital of Philadelphia. "We found that three-quarters of these high-risk infants have episodes of surfactant dysfunction, and these episodes are associated with worsening of their respiratory status."
Surfactant is a naturally produced mixture of proteins and lipids (fats) that lowers surface tension within alveoli, the tiny air sacs within the lungs. By doing so, it prevents the alveoli from collapsing during exhalation, and eases the work of breathing. Premature infants have underdeveloped respiratory systems and do not produce enough of their own surfactant. Therefore, physicians have found that supplying replacement surfactant may improve infants' lung function during the earliest period after birth.
Replacement surfactant is discontinued after babies begin to produce enough surfactant on their own. However, infants with persistent lung disease may develop a condition called bronchopulmonary dysplasia (BPD), in which chronic respiratory distress makes it necessary for infants to breathe through a mechanical ventilator. BPD can cause long-term disability or death.
In this study, the researchers analyzed samples of fluid from the windpipes of 68 premature infants who had breathing tubes between one to 12 weeks after birth. Seventy-five percent of the infants on at least one occasion had abnormal surfactant function, and diminished amounts of an important component of surfactant, called surfactant protein B. In addition, these surfactant abnormalities were significantly more likely to occur during periods of respiratory infection and worsened respiratory status.
Babies are defined as premature if they are born before 37 weeks of gestation. Most premature babies have symptoms of respiratory distress, with the risk increasing with greater prematurity. The infants in this study were very premature, having been born at 23 to 30 weeks gestation.
"Premature infants with continuing respiratory failure and abnormal surfactant may benefit from treatment with replacement surfactant--or from strategies to increase their own production of surfactant," said Dr. Ballard, who has been studying infant lung development for more than 30 years. He and his colleagues are currently carrying out a pilot trial of surfactant therapy in preterm infants older than 7 days, and they are planning a clinical trial to investigate short- and long-term safety and effectiveness of surfactant treatment in these infants.
The National Institutes of Health and endowed chairs at The Children's Hospital of Philadelphia and Children's Mercy Hospital supported the study. Philadelphia supported the study. Dr. Ballard's co-authors were Jeffrey D. Merrill, M.D., Roberta A. Ballard, M.D., Avital Cnaan, Ph.D., Anna Maria Hibbs, M.D., Rodolfo I. Godinez, M.D., Ph.D., and Marye H. Godinez, M.D., of Children's Hospital and the University of Pennsylvania School of Medicine; and William E. Truog, M.D., of the University of Missouri-Kansas City School of Medicine and Children's Mercy Hospital of Kansas City, Mo.
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