Interpretation of Blood Gases
Physiology of gas exchange
Oxygenation. The movement of O 2 from the alveolus into the blood is dependent upon the matching of ventilation and perfusion. Ventilation/perfusion matching is abnormal if:
Pulmonary blood flows past unventilated alveoli, causing an intrapulmonary right-to-left shunt. In newborns, this is typically caused by atelectasis. The treatment for atelectasis is positive pressure, which opens previously unventilated alveoli and decreases intrapulmonary shunting.
Blood flows right-to-left through the foramen ovale or patent ductus arteriosus, causing an extrapulmonary right-to-left shunt. This sort of extrapulmonary shunt is typically caused by elevated pulmonary vascular resistance (pulmonary hypertension), and can be treated by decreasing pulmonary vascular resistance (e.g., with inhaled nitric oxide).
Ventilation. Ventilation is the removal of CO 2 from the blood.
During spontaneous breathing or conventional mechanical ventilation, the...