Persistent pulmonary hypertension (PPHN) occurs when some factors prevent the normal transition to extrauterine life. This results from the failure of the pulmonary vascular resistance, which is supposed to decrease. This life-threatening condition is aggressively treated with high concentrations of oxygen, inhaled nitric oxide, and pharmacological agents such sildenafil. Transient tachypnea of the newborn (TTN) occurs when fluid is not completely absorbed by the lungs and results in tachypnea for a day or two after birth. Extremely premature babies, not full-term babies, require time for their lungs to develop before being able to breathe without the ventilator. Although the minimum oxygen therapy is generally used in order to prevent cellular damage from free radical oxygen species, the baby with PPHN requires high concentrations of oxygen to help relax the pulmonary vasculature.