Acute Hypoxaemic Respiratory Failure and Acute Respiratory Distress Syndrome

Acute hypoxaemic respiratory failure (AHRF) constitutes a group of conditions characterized by the acute onset of severe hypoxaemia, increased respiratory work, leading to respiratory failure. AHRF causes range from ARDS, to acute viral or bacterial pneumonia, to infectious exacerbations asthma or COPD, and even to extrinsic pathologies such acute heart failure induced hydrostatic pulmonary oedema. ARDS is a clinical syndrome characterized by inflammation induced diffuse alveolar damage resulting in permeability pulmonary oedema. The current ‘Berlin’ ARDS definition includes criteria regarding timing of onset, chest imaging findings, origin of the oedema, underlying predisposing factors, and hypoxaemia severity. In contrast, ‘other cause’ AHRF constitutes a more ill-defined entity, with no broadly agreed criteria for definition. Mortality rates remain high, at 40% in patients requiring critical care irrespective of the type of AHRF, despite encouraging advances in management. This chapter focuses on patients with AHRF due to ARDS and other acute pulmonary causes. We will explore our current understanding of the definitions of these conditions and propose a simple ‘operational’ definition for AHRF. We explore the epidemiology and pathophysiology of AHRF and ARDS. We will critically assess current management approaches, including the extrapolation of management approaches from ARDS to patients with other causes of AHRF. We will address outcomes from different types of AHRF, and whether how mortality relates to the underlying cause versus the extent of lung pathology. We will then identify key challenges to be addressed to improve the outcomes from these devastating clinical conditions.