The multicenter Nitric Oxide Chronic Lung Disease Study Group (NOCLD) published the study in the July 27 New England Journal of Medicine.
In addition to the clinical benefits, the researchers found no apparent adverse effects from the nitric oxide up to 44 weeks of age. "Survival for premature infants has greatly improved over the years, but long-term complications often persist in these children," said Elizabeth G. Nabel, MD, director of the National Heart, Lung and Blood Institute of the National Institutes of Health, which funded the five-year study. She added, "Successful and early treatment of breathing problems in these babies could represent a significant advance in improving the health and quality of life of a growing number of premature babies."
An estimated 10,000 to 15,000 infants in the United States have chronic lung disease of prematurity. Ongoing medical care for these infants, such as multiple hospitalizations, prolonged respiratory treatments and follow-up for neurodevelopmental problems, accounts for a significant portion of the overall public health burden of prematurity. In a report released this month, the Institute of Medicine estimated that overall costs for the more than 500,000 babies born prematurely in the U.S. totaled $26 billion, or $51,000 per infant.
The NOCLD clinical trial included 21 neonatal intensive care units throughout the country, enrolling infants with birth weights between 500 and 1250 grams, or about one to three pounds. Their median gestational age was 26 weeks (full-term babies are born at about 40 weeks gestational age). All the infants were receiving oxygen through ventilators and were at high risk of developing chronic lung disease, also known as bronchopulmonary dysplasia, because their lungs were immature and underdeveloped. In this condition, scarring and inflammation in lung tissue make breathing difficult, and the infant often requires prolonged mechanical ventilation and hospitalization.
Although treatment with nitric oxide, a substance naturally produced in the body, is already known to benefit full-term infants with pulmonary hypertension, its value for preterm infants was uncertain. "The mechanism by which nitric oxide affects the lungs is not fully understood," said Dr. Ballard, "but animal studies and pilot studies in infants previously suggested that nitric oxide restores normal growth and development in very immature lungs."
The trial was randomized and double-blinded, with 294 infants receiving inhaled nitric oxide and 288 receiving a placebo. The rate of survival without chronic lung disease at 36 weeks after the mother's last menstrual period was 43.9 percent in treated infants compared to 36.8 percent in the control group.
The effect was more pronounced for the infants entered earlier (between seven and 14 days): 49.1 percent in treated infants vs. 27.8 percent in controls. Lung disease was also less severe in treated infants at 40 and 44 weeks, with treated infants having shorter hospitalizations and less need for mechanical ventilation or oxygen therapy than the control infants.
The NOCLD team expects to provide definitive recommendations for clinical use of nitric oxide after it analyzes follow-up studies of the children's neurodevelopmental status at two years of age. The follow-up studies will be accomplished by the end of 2007, said Dr Ballard.