Respiratory failure is a condition of impaired gas exchange in which the circulatory system fails to provide sufficient oxygenated blood to the organs (hypoxemia), fails to remove sufficient carbon dioxide (hypercapnia), or a combination of both.

Respiratory failure may be classified as an acute, severe, sudden-onset medical emergency, or as chronic, which develops over a period of time and necessitates long-term treatment. Chronic respiratory failure occurs in association with chronic obstructive pulmonary disease (COPD) or chronic drug- or alcohol-induced respiratory suppression. Broadly, respiratory failure is also classified into 4 major classes based on the underlying etiology of the condition.

Type I respiratory failure is characterized by hypoxemia-damaged lung tissue. Several mechanisms cause such severe hypoxemia, including ventilation perfusion mismatch (pulmonary edema, pulmonary embolism, or chronic lung disease), right-to-left shunting (acute respiratory distress, pneumonia, edema, or congenital heart defect), or diffusion impairment (interstitial lung diseases).

Type II respiratory failure, or ventilation failure, is characterized by hypercapnia, high levels of carbon dioxide in the circulating blood, or respiratory acidosis, which can be fatal if untreated. Possible underlying causes include pre-existing chronic lung conditions (COPD, asthma, cystic fibrosis, etc), impaired central respiratory drive (traumatic or drug-related), neuromuscular diseases (myopathies, myasthenia gravis, Guillain-Barré syndrome), spinal cord injury, sepsis, diabetic ketoacidosis, or hyperthermia.

Type III respiratory failure involves perioperative atelectasis secondary to low functional residual capacity. This can result in hypoxia, hypercarbia, or both. It can be prevented with pulmonary toileting and effective pain management for postoperative patients.

Type IV occurs following intubation and recovery from hypoperfusion-related injury or shock.

Depending on the root cause of respiratory failure, treatments include treating the causative disease, oxygen therapy, mechanical ventilation, and tracheostomy.