[What Should We Know about Respiratory Physiology for the Optimal Anesthesia Management?]

Gas exchange in the lungs is dependent on the balance between ventilation and pulmonary perfusion, and such balance could be modified and affected by various factors, including gravity, body position, physical property of the lung, and neurological as well as humoral factors. Oxygenation is the process where the oxygen molecule moves from alveoli to the blood plasma, and this process is highly dependent on the diffusion capacity. Although the oxygen partial pressure in the blood plasma at alveoli rises rapidly because of its very low solubility, hemoglobin is essential to maintain adequate oxygen content in the whole blood. When a part of the lung has atelectasis, pulmonary shunt and desaturation of arterial blood ensue. For the optimal patient care, atelectasis and pulmonary shunt should be taken care of well with thorough monitoring. Ventilation is the process where carbon dioxide (CO2) moves from blood plasma to alveoli, and can eliminate CO2, produced by metabolism. The understanding of ventilator-induced lung injury (VILI) during acute respiratory failure leads us to ventilate the lungs in less harmful way, with lung protective ventilation, and the most important factor is driving pressure (inspiratory plateau pressure-PEEP). When the ventilator setting should be adjusted in order to maintain adequate ventilation, the respiratory frequency is essential to adjust alveolar ventilation without affecting driving pressure.