並列摘要
The lung is important organ for gas exchange, including absorb oxygen from atmosphere and eliminate carbon dioxide to atmosphere. For adequate gas exchange, it need matching between ventilation and perfusion. Clinically, among patients with hypoxemia and hypercapnia, evaluation of ventilation-perfusion ratio could define etiology and follow up therapeutic effect. Dead space was defined as alveoli which have ventilation but not perfusion. It could be subdivided into airway or alveolar dead space depend on anatomical location. The former correlates with emphysema and ventilator circuits. The later has been already proved to diagnose pulomonary embolism, choose optimal positive end-expiratory pressure, predict successful weaning, and evaluate prognosis and therapeutic effect of acute respiratory distress syndrome. Evaluating dead space ratio adequately could improve clinical care.