Airway pressure release ventilation in the acute respiratory distress syndrome following traumatic injury.

Abstract

Respiratory insufficiency that occurs following a traumatic injury is due to both mechanical and physiological disruption of pulmonary integrity. Although an overall decrease in pulmonary compliance (Δ V/Δ P) is a component of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS)*, this may not be a homogeneous process. Changes in compliance may actually occur at varying degrees throughout the lung parenchyma in a heterogeneous fashion. Attempting to open or recruit collapsed alveoli without causing lung injury by overdistention or stretch of alveoli with more normal compliance remains a clinical challenge. Airway pressure release ventilation (APRV) is a ventilator mode that incorporates features that optimize the spectrum of alveolar mechanics present in ARDS/ALI. In the past, the focus on ventilator support was on conforming the patient to the ventilator; alternatively, APRV accommodates the patient's breathing pattern and superimposes ventilation onto a pressure framework to support spontaneous breathing, 1 - 3 and thereby conforms the ventilator to the patient. APRV differs from other modes of positive-pressure ventilation in that it delivers a continuous positive airway pressure (CPAP) that releases periodically to augment CO 2 exchange. The patient's breathing is spontaneous and unrestricted throughout the entire ventilator cycle, allowing infinite inspiratory/expiratory ratios. Studies have shown that APRV can augment ventilation with lower pulmonary artery pressures and improved efficiency compared to traditional modes of ventilatory support; these elements may reduce the risk of ventilator-associated lung injury while improving oxygenation. After a brief review of the incidence and outcome of traumatic ARDS, we will present basic concepts of ventilator management with APRV and then will address the use of APRV in the patient with respiratory failure secondary to trauma.