Neonatal chronic lung disease (CLD) is usually diagnosed if an infant remains oxygen dependent beyond 36 weeks postconceptional age (PCA). Our aim was to determine whether a shorter duration of respiratory support accurately predicted subsequent respiratory morbidity. A total of 103 infants, median gestational age 29 weeks (range 23-35), were followed prospectively for 5 years. They had a birth weight of < 1500 g or, if a birth weight of between 1500 and 2000 g, had required neonatal ventilatory support. Parents completed diary cards; their child had positive symptom status if, in any one year, they coughed and/or wheezed on at least 3 days per week for a 4-week period or for at least 3 days following each upper respiratory tract infection. Subsequent respiratory morbidity, positive symptom status in years 1 and 2 or all 5 pre-school years, was related to various definitions of prolonged respiratory support: intermittent positive pressure ventilation dependence > 7 days; oxygen dependence > 28 days and oxygen dependence > 36 weeks PCA. In years 1 and 2, 25 children were symptomatic and 22 in all 5 years. The patients with subsequent respiratory morbidity were distinguished from those without by requiring longer respiratory support (P < 0.05). Logistic regression analysis demonstrated only oxygen dependence beyond 28 days was independently related to subsequent respiratory morbidity (P < 0.01). The positive predictive values and likelihood ratios (95% confidence intervals) for positive symptom status in all 5 years were for intermittent positive pressure ventilation > 7 days 35% (16-53) and 19.5 (1.01-3.76), for oxygen dependency > 28 days 42% (23-61) and 2.20 (1.45-5.02) and for oxygen dependency >36 weeks PCA 35% (13-58) and 1.67 (0.65-4.31).
Conclusion: Oxygen dependency at 28 days of age remains a useful criterion on which to diagnose "neonatal" chronic lung disease.