In stage 1 (1-3 days), the pathologic appearances of BPD are identical to those of respiratory distress syndrome where there is not enough surfactant in the lungs. Surfactant helps to lower surface tension in the airways and this helps keep the lung alveoli open. It involves the presence of hyaline membranes, atelectasis, vascular hyperemia, and lymphatic dilatation, (E-Medicine, 2009).