CPAP of 4 cm H2O Has No Short-Term Benefit at Term in Infants with BPD

Abstract

Background: Lung development and function is compromised at term in infants with bronchopulmonary dysplasia (BPD), characterized by reduced functional residual capacity (FRC) and impaired gas-mixing efficiency in distal airways. Objective: To determine whether continuous positive airway pressure (CPAP) improves FRC, ventilation, distal airway function, and gas exchange in spontaneously breathing infants with BPD. Design/Methods: Twenty-one infants with BPD (median birth weight 0.72 kg (range 0.50–1.27) and median gestational age 26 weeks (range 23–28)) were studied before and after CPAP of 4 cm H₂O was applied by a facemask system. A multiple-breath nitrogen washout method was used to assess FRC, ventilation, and gas-mixing efficiency. Moment analysis and lung clearance index was calculated from the nitrogen-decay curve for assessment of gas-mixing efficiency. Transcutaneous (Tc) PO₂/PCO₂ was monitored during stable infant conditions before each washout test. Results: When CPAP was raised from 0 to 4 cm H₂O, FRC increased significantly together with a significant increase in moment ratios (M₁/M₀ and M₂/M₀). Tc PO₂ decreased significantly and the breathing pattern changed, with significantly reduced respiratory rate, minute ventilation, and alveolar ventilation. There was also an increase in tidal volume and dead space. Conclusions: CPAP of 4 cm H₂O applied with a facemask at term to infants with BPD did not improve ventilation, gas-mixing efficiency in distal airways, or oxygenation despite an increase in FRC. We speculate that instead of promoting recruitment of unventilated lung volumes, increasing the end-expiratory pressure in infants with BPD may lead to an overexpansion of already ventilated parts of the lung, causing further compromise of lung function.