Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Respiratory Failure

(Lung Failure)


Bhakti K. Patel

, MD, University of Chicago

Last full review/revision Apr 2020| Content last modified Apr 2020
Click here for the Professional Version
Topic Resources

Respiratory failure is a condition in which the level of oxygen in the blood becomes dangerously low or the level of carbon dioxide in the blood becomes dangerously high.

  • Conditions that block the airways, damage lung tissue, weaken the muscles that control breathing, or decrease the drive to breathe may cause respiratory failure.

  • People may be very short of breath, have a bluish coloration to the skin, and be confused or sleepy.

  • Doctors use a fingertip sensor (pulse oximetry) to detect low levels of oxygen and blood tests to detect high levels of carbon dioxide in the blood.

  • Oxygen is given.

  • Sometimes people need the help of a machine to breathe until the underlying problem can be treated.

Acute respiratory failure is a medical emergency that can result from

  • Long-standing lung disease that suddenly gets worse

  • Severe lung disease that develops suddenly in otherwise healthy people

An example of lung disease that develops suddenly is acute respiratory distress syndrome.

Chronic respiratory failure is an ongoing breathing problem that can result from long-standing lung disease such as chronic obstructive pulmonary disease (COPD).

Causes of Respiratory Failure

Almost any condition that affects breathing or the lungs can lead to respiratory failure. Respiratory failure can occur in two ways:

  • The level of oxygen in the blood becomes too low (hypoxemic respiratory failure).

  • The level of carbon dioxide in the blood becomes too high (hypercarbic respiratory failure).

Sometimes people have both low oxygen and high carbon dioxide levels.


What Causes Respiratory Failure?

Underlying Problem


Abnormality of the chest wall

A chest wound, deformities resulting from chest surgery, injury, extreme obesity, or scoliosis

Abnormality of lung tissue

Acute respiratory distress syndrome (ARDS), a drug reaction, pneumonia, pulmonary edema (excess fluid in the lungs) due to heart failure or kidney failure, pulmonary fibrosis, radiation, sarcoidosis, or widespread tumors

Airflow obstruction

Muscle weakness

Poor breathing (decrease in the drive to breathe)

Drug or alcohol intoxication, hypothyroidism, obesity, or sleep apnea

Low oxygen level (hypoxemic respiratory failure)

A common cause of hypoxemic respiratory failure is an abnormality of the lung tissue, such as acute respiratory distress syndrome, severe pneumonia, excess fluid in the lungs (for example, caused by heart failure or kidney failure), or lung scarring. Such abnormalities disrupt the usual ability of the lung tissues to take in oxygen from the air.

Hypoxemic respiratory failure can also occur if blood flow through the lungs becomes abnormal, as happens when a blood clot blocks a lung artery (pulmonary embolism). This disorder does not disrupt the usual ability of the lung tissues to take in oxygen, but without blood flowing to a portion of the lungs, oxygen is not properly extracted from the air.

High carbon dioxide level (hypercarbic respiratory failure)

With hypercarbic respiratory failure, the level of carbon dioxide is usually too high because something prevents the person from breathing normally. Common examples of such causes include the following:

  • A low level of thyroid hormone (hypothyroidism)

  • Sedation due to an overdose of opioids or alcohol

  • Blockage or narrowing of the airways

  • Injury to the lungs

  • Damage to bones and tissues around the lungs

  • Weakness of muscles that normally inflate the lungs

Hypothyroidism, sleep apnea, and an overdose of opioids or alcohol all decrease the unconscious reflex that drives people to breathe. Blockage or narrowing of the airways can result from disorders (such as asthma and chronic obstructive pulmonary disease) as well as inhaled foreign objects.

People who are not breathing adequately also may have a low oxygen level, but they are not considered to have hypoxemic respiratory failure if they do not also have a disorder of their lung tissue.

High levels of carbon dioxide tend to cause the blood to become acidic.

Did You Know?

  • Age-related reductions in lung function place older people at higher risk of severe symptoms after developing pneumonia

Symptoms of Respiratory Failure

Hypoxemic respiratory failure and hypercarbic respiratory failure often cause similar symptoms. People are usually very short of breath. Low oxygen levels in the blood cause shortness of breath and result in a bluish coloration to the skin (cyanosis). Low oxygen levels, high carbon dioxide levels, and increasing acidity of the blood cause confusion and sleepiness. If the drive to breathe is normal, the body tries to rid itself of carbon dioxide by deep, rapid breathing. If the lungs cannot function normally, however, this breathing pattern may not help. Eventually, the brain and heart malfunction, resulting in drowsiness (sometimes to the point of becoming unconscious) and abnormal heart rhythms (arrhythmias), both of which can lead to death.

Some symptoms of respiratory failure vary with the cause. If the drive to breathe is abnormal (for example, after an overdose of alcohol or sedatives), people may be extremely sleepy, breathe too slowly, and quietly slip into a coma. A child with an obstructed airway due to the inhalation (aspiration) of a foreign object (such as a coin or a toy) may suddenly gasp and struggle for breath.

Diagnosis of Respiratory Failure

  • Measurements of the amount of oxygen and carbon dioxide in the blood

  • Chest x-ray and other tests to determine the cause

A doctor may suspect respiratory failure because of the symptoms and physical examination findings.

The level of oxygen in the blood can be measured without taking a blood sample by using a sensor placed on a finger or an earlobe—a procedure called pulse oximetry.

A test done on a sample of blood taken from an artery confirms the diagnosis of respiratory failure when it shows a dangerously low level of oxygen and/or a dangerously high level of carbon dioxide.

Chest x-rays and usually other tests are done to determine the cause of respiratory failure.

Treatment of Respiratory Failure

  • Supplemental oxygen

  • Mechanical ventilation

  • Treatment of the cause

People with acute respiratory failure are treated in an intensive care unit (ICU).

Supplemental oxygen is given to correct any lack of oxygen in people with respiratory failure. Oxygen can be given using small plastic prongs placed in the nose (nasal cannula) or using a face mask, depending on how much oxygen people need. Oxygen is usually given initially in a greater amount than is needed and adjusted down later.

Mechanical ventilation corrects the problem of ventilating the lungs (and decreases carbon dioxide levels) in people with hypercarbic respiratory failure. In mechanical ventilation, a machine (ventilator) is used to help air get in and out of the lungs. The air is delivered under pressure from the machine through a face mask (noninvasive positive pressure ventilation) or through a tube placed in the windpipe (invasive positive pressure ventilation). Doctors often try noninvasive methods first, but invasive mechanical ventilation may be necessary unless respiratory failure resolves rapidly with noninvasive treatment. Most people with respiratory failure are treated with both supplemental oxygen and some kind of mechanical ventilation.

The underlying disorder causing the respiratory failure must be treated. For example, antibiotics are used to fight pneumonia caused by bacterial infection, and bronchodilators are used in people with asthma to open the airways. Other drugs may be given, for example, to decrease inflammation or treat blood clots.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version


Others also read

Test your knowledge

Goodpasture Syndrome
Goodpasture syndrome is an uncommon autoimmune disorder in which bleeding into the lungs and progressive kidney failure occur. People with the syndrome usually have difficulty breathing and cough up blood. Which of the following groups is most likely to developing Goodpasture syndrome?
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID