Meconium has the potential to wreak havoc when it contaminates the lower airway of a newborn. First, when the particulate material becomes trapped in small distal airways, it tends to function as a ball valve—permitting air to enter alveoli, but not evacuate, thus resulting in ventilation/perfusion (V/Q) imbalance and overinflation of the lung. The abnormally high lung volume predisposes to development of air leaks, such as pneumothorax or pulmonary interstitial emphysema. Second, if the meconium reaches the alveoli, it will inactivate endogenous surfactant, thus leading to atelectasis and further contributing to V/Q mismatch. Overdistension of the lung through air trapping and ventilator therapy may also damage alveolar integrity, leading to leakage of serum proteins and further inactivation of surfactant. Third, the hypoxemia resulting from the airway problems may result in pulmonary vasoconstriction, thus leading to extrapulmonary right-to-left shunting and more V/Q mismatch. Therefore, there are many reasons why the concept...

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