Principles of Critical Care > Part IV. Pulmonary Disorders > Chapter 38. Acute Lung Injury and the Acute Respiratory Distress Syndrome Jason D. Christie,  Paul N. Lanken

Key Points

"Severe arterial hypoxemia that is resistant to supplemental oxygen is a common reason for admission to the ICU. This form of respiratory failure, termed acute hypoxemic respiratory failure (AHRF), arises from widespread flooding or collapse of alveoli. As a result, a substantial fraction of mixed venous blood traverses nonventilated alveoli (i.e., alveoli with ventilation-perfusion ratio of 0). This in turn results in a large right-to-left intrapulmonary shunt (Fig. 38-1). In addition to its adverse effects on oxygenation, fluid that accumulates in alveoli and interstitial tissues increases lung stiffness, which decreases lung compliance. This imposes a larger mechanical load on the patient's respiratory system, resulting in an increased elastic work of breathing. Without treatment with supplementary oxygen and assisted ventilation, the gas exchange derangement and abnormal lung mechanics can result in progressive hypoxemia, respiratory muscle fatigue, and eventual respiratory arrest and death...."