Pathophysiology
Clinical meaning
Pulmonary surfactant is a complex mixture of phospholipids (90%, primarily DPPC - dipalmitoylphosphatidylcholine) and surfactant proteins (SP-A, SP-B, SP-C, SP-D). Type II pneumocytes begin producing surfactant at 24-28 weeks but adequate amounts not present until 34-36 weeks. Surfactant reduces alveolar surface tension according to LaPlace's Law (P = 2T/r), preventing atelectasis. Without it, high opening pressures are needed, causing barotrauma and oxygen toxicity leading to BPD.