Respiratory failure

The respiratory system consists of two main components: the lungs and the respiratory muscle pump. Respiratory failure is the consequence of lung failure leading to hypoxaemia, or respiratory muscle pump failure resulting in hypercapnia. Type 1 respiratory failure (hypoxaemic respiratory failure) is defined as a partial pressure of arterial oxygen (PaO2) less than 8.0 kPa, and type 2 respiratory failure (hypercapnic respiratory failure) as PaO2 less than 8 kPa and a partial pressure of arterial carbon dioxide (PaCO2) over 6 kPa. Diagnosis is made easier by understanding the pathophysiological mechanisms that cause hypoxaemia and hypercapnia. Furthermore, a basic knowledge of acid–base balance allows distinction between acute, acute-on-chronic and chronic type 2 respiratory failure. In addition to the standard assessment, careful consideration must be given to neurological conditions as well as obstructive sleep apnoea as these are frequently overlooked causes of respiratory failure. Imaging and pulmonary function tests provide useful information to ascertain the diagnosis. Management of these patients will depend on the underlying cause, but the objective of treatment must be to improve oxygenation and/or ventilation to resolve hypoxaemia and hypercapnia.