1 Introduction

Managing respiratory dysfunction is a fundamental aspect of critical care medicine. Although respiratory failure is a rare cause of death in the intensive care unit (ICU)1, the vast majority of patients admitted to the ICU experience respiratory dysfunction2. This introductory chapter focuses on pulmonary mechanics as related to critical care and pulmonary gas exchange, V/Q relationships, dead space, shunting, and evaluation of hypoxemia and hypercarbia. Such knowledge provides a framework that clarifies the rationale behind the various approaches to mechanical ventilatory support.