Correlation of radiographic thoracic area and oxygenation impairment in bronchopulmonary dysplasia

• Hyperinflation can be radiographically assessed by the radiographic thoracic area.
• In premature infants with developing bronchopulmonary dysplasia the radiographic thoracic area is significantly related to the ventilation/perfusion inequality.
• This probably reflects the evolving architectural distortion in bronchopulmonary dysplasia.

We hypothesized that radiographically-assessed hyperinflation in bronchopulmonary dysplasia (BPD) is related to the degree of oxygenation impairment. Our objective was to explore the relation of chest radiographic thoracic area (CRTA) with right-to-left shunt, right shift of the oxyhemoglobin dissociation curve and ventilation/perfusion ratio (VA/Q) in infants with BPD. Twenty-two infants born at median (IQR) gestation of 26 (24–28) weeks with BPD were prospectively studied at 39 (30–69) days. Inspired oxygen (FiO2) was varied to obtain transcutaneous oxygen saturation (SpO2) values between 85 and 96%. Shunt, shift and VA/Q were derived by plotting and analysing pairs of SpO2 and FiO2. CRTA was measured by free hand-tracing the perimeter of the thoracic area in anterio–posterior chest radiographs. Median (IQR) shunt was 8 (1–14)%, shift was 13 (11–19) kPa and VA/Q 0.42 (0.30–0.48). Median (IQR) CRTA/kg was 2495 (1962–2838) mm2 and was significantly related to shift (r = 0.674, p < 0.001), VA/Q (r = −0.633, p < 0.001), weight at study (r = −0.457, p = 0.003) and day of life (r = −0.406, p = 0.009), but not to shunt. CRTA in BPD is significantly related to oxygenation impairment as quantified by shift and VA/Q. CRTA can be used as a simple radiographic test to quantify BPD severity.