Introduction

Acute respiratory distress syndrome (ARDS) is characterized pathophysiological^ by increased intrapulmonary shunt and ventilation-perfusion imbalances, increased intrapulmonary dead space, and decreased respiratory system compliance. Most ARDS patients experience hypoxemia while ventilating spontaneously, even with high fractions of inspired oxygen (FiO2). Many patients cannot sustain adequate ventilation, leading to hypercapnia, respiratory acidosis, and worsening hypoxemia. Without mechanical ventilation, death may occur within a short time. With mechanical ventilation, adequate ventilation and oxygenation can be sustained in most patients, providing more time for administration of specific treatments such as antibiotics for infections and for natural healing. However, mechanical ventilation may also cause acute lung injury (ventlation-associated or ventilator-induced lung injury, VILI). Thus, our primary means of respiratory support, which is criticalfor survival of most patientswith ARDS,mayparadoxicallyprevent recovery of some patients.

Many studies in experimental animal models suggested that some specific aspects of mechanical ventilation techniques are responsible for VILI, and that modifications of mechanical ventilation approaches could decrease or prevent VILI [1-9]. However, these modifications could also have adverse effects on respiratory or circulatory function which could be detrimental to recovery of ARDS patients. Therefore, clinical trials were necessary to demonstrate the value of different mechanical ventilation strategies for improving important clinical outcomes. This chapter summarizes the rationale for the modified mechanical ventilation strategies and the results of several randomized clinical trials designed to compare clinical outcomes among patients who received different mechanical ventilation approaches.

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