Respiratory failure is a condition in which there is a fall in the blood oxygen level (see hypoxia) caused by the inadequate exchange of gases in the lungs. Respiratory failure may have a number of causes: lung disorders such as severe asthma or pneumonia; depression of the respiratory center in the brainstem due, for example, to an overdose of opioid analgesic drugs; a stroke, or a head injury; damage to the chest wall, such as flail chest; and nerve and muscle diseases that affect breathing, including poliomyelitis.

The symptoms of respiratory failure include breathlessness, cyanosis (bluish coloration of the skin), confusion, and agitation. Treatment is for the underlying cause, and oxygen and/or assisted ventilation may also be given if required. In some cases, a respiratory stimulant drug may be prescribed.