Fig. 2: Anatomic and physiologic pulmonary differences in extremely preterm infants.

The canalicular stage lung with surfactant deficiency, reduced elastin and fewer pores of Kohn and canals of Lambert increases tendency to collapse. Hypoxemia and brain pathology such as intraventricular hemorrhage (IVH) lead to respiratory depression. A relatively large, floppy epiglottis and laryngotracheobronchomalacia contribute to airway obstruction. Soft, compliant chest wall, stiff lungs, horizontal rib alignment and a flat diaphragm with fewer type I muscle fibers prevent achieving and sustaining functional residual capacity (FRC). Respiratory depression, failure to sustain FRC and presence of right-to-left atrial and ductal shunts contribute to hypoxemia. Copyright Satyan Lakshminrusimha.