Do clinical markers of barotrauma and oxygen toxicity explain interhospital variation in rates of chronic lung disease? The Neonatology Committee for the Developmental Network

Abstract

Objective: To explore the hypothesis that variation in respiratory management among newborn intensive care units (NICUs) explains differences in chronic lung disease (CLD) rates.

Design: Case-cohort study.

Setting: NICUs at 1 medical center in New York (Babies' and Children's Hospital [Babies']) and 2 in Boston (Beth Israel Hospital and Brigham and Women's Hospital [Boston]).

Study population: Four hundred fifty-two infants born at 500 to 1500 g birth weight between January 1991 and December 1993, who were enrolled in an epidemiologic study of neonatal intracranial white matter disorders.

Case definition: Supplemental oxygen required at 36 weeks' postmenstrual age.

Results: The prevalence rates of CLD differed substantially between the centers: 4% at Babies' and 22% at the 2 Boston hospitals, despite similar mortality rates. Initial respiratory management at Boston was more likely than at Babies' to include mechanical ventilation (75% vs 29%) and surfactant treatment (45% vs 10%). Case and control infants at Babies' were more likely than were those at Boston to have higher partial pressure of carbon dioxide and lower pH values on arterial blood gases. However, measures of oxygenation and ventilator settings among case and control infants were similar at the 2 medical centers in time-oriented logistic regression analyses. In multivariate logistic regression analyses, the initiation of mechanical ventilation was associated with increased risk of CLD: after adjusting for other potential confounding factors, the odds ratios for mechanical ventilation were 13.4 on day of birth, 9.6 on days 1 to 3, and 6.3 on days 4 to 7. Among ventilated infants, CLD risk was elevated for maximum peak inspiratory pressure >25 and maximum fraction of inspired oxygen = 1.0 on the day of birth, lowest peak inspiratory pressure >20 and maximum partial pressure of carbon dioxide >50 on days 1 to 3, and lowest white blood count <8 K on days 4 to 7. Even after adjusting for white blood count <8 K and the 4 respiratory care variables, infants in Boston continued to be at increased risk of CLD, compared with premature infants at Babies' Hospital.

Conclusion: In multivariate analyses, a number of specific measures of respiratory care practice during the first postnatal week were associated with the risk of a very low birth weight infant developing CLD. However, after adjusting for baseline risk, most of the increased risk of CLD among very low birth weight infants hospitalized at 2 Boston NICUs, compared with those at Babies' Hospital, was explained simply by the initiation of mechanical ventilation.