Section 4. Lung and Airway Disorders

Chapter 55. Respiratory Failure

Topic: Respiratory Failure

Respiratory Failure

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

Respiratory failure, which is a medical emergency, is often the final stage of chronic lung disease. Respiratory failure can also result from severe, sudden lung disease (such as acute respiratory distress syndrome (see Section 4, Chapter 56)) in otherwise healthy people. Almost any condition that affects breathing or the lungs can lead to respiratory failure. An overdose of opioids or alcohol can cause such profound sedation that a person stops breathing and suffers respiratory failure. Obstruction of the airways, injury to the lung tissues, damage to the bones and tissues around the lungs, and weakness of the muscles that normally inflate the lungs are also common causes. Respiratory failure can occur if blood flow through the lungs becomes abnormal, as happens in pulmonary embolism (see Section 4, Chapter 46). This disorder does not stop air from moving in and out of the lungs, but without blood flow to a portion of the lungs, oxygen is not properly extracted from the air.

Symptoms and Diagnosis

Low oxygen levels in the blood cause a bluish coloration (cyanosis), and high carbon dioxide levels and increasing acidity of the blood cause confusion and sleepiness. The body tries to rid itself of carbon dioxide by deep, rapid breathing, but if the lungs cannot function normally, this breathing pattern may not help. Eventually low levels of oxygen make the brain and heart malfunction, resulting in deteriorating consciousness or unconsciousness and abnormal heart rhythms (arrhythmias), which can lead to death.

Some symptoms of respiratory failure vary with the cause. A child with an obstructed airway due to the inhalation (aspiration) of a foreign object may gasp and struggle for breath (see Section 24, Chapter 299); someone who is intoxicated or weak may quietly slip into a coma.

A doctor may suspect respiratory failure from the symptoms and examination. A blood test confirms the diagnosis when it shows a dangerously low level of oxygen or a dangerously high level of carbon dioxide.

If respiratory failure develops slowly, pressure in the blood vessels of the lungs increases, a condition called pulmonary hypertension (see Section 4, Chapter 54). If left untreated, this condition damages the blood vessels, further impairs the transfer of oxygen to the blood, and stresses the heart, causing heart failure.

See the table What Causes Respiratory Failure?

Treatment

Almost always, oxygen is given initially. Usually, the amount given is more than is needed, but this can be readjusted at a later time. In people with chronically high carbon dioxide levels, excess oxygen can result in slowing of the movement of air (ventilation) in and out of the lungs and a dangerous further increase in the carbon dioxide level. In such people, the dosage of oxygen needs to be more carefully regulated.

The underlying cause of the respiratory failure must also be treated. Antibiotics are used to fight infection, and bronchodilators are used to open the airways. Other drugs may be given to decrease inflammation or prevent blood clots.

Mechanical Ventilation: Some very ill people need mechanical ventilation to aid breathing. Mechanical ventilation can be lifesaving whenever people are not able to move enough air in and out of their lungs. A plastic tube is inserted through the nose or mouth into the trachea; this tube is attached to a machine that forces air into the lungs. Exhalation occurs passively because of the elastic recoil of the lungs. Many types of ventilators and modes of operation may be used, depending on the underlying disorder. If the lungs are not functioning well, additional oxygen may be delivered through the ventilator. In people who do not require complete support of their breathing, a mask may be placed over the nose or face, which permits the delivery of positive pressure, thus assisting the person's own breathing efforts and preventing fatigue of the respiratory muscles. In about half of the people with respiratory failure, use of these techniques (called bi-level positive airway pressure or continuous positive airway pressure) can avoid the need to intubate the trachea. Use of bi-level positive airway pressure at night can help people whose respiratory failure was caused by muscle weakness, because after resting at night, the respiratory muscles are able to function more effectively during the day.

The amount of fluid in the body must be carefully monitored and adjusted to maximize lung and heart function. The acidity of the blood must be kept in balance by adjusting the frequency and size of breaths delivered by the ventilator. A person undergoing mechanical ventilation may experience agitation, which can be controlled with sedating drugs such as lorazepam and midazolam or opioids such as morphine or fentanyl. Bacterial infections that may develop while the person undergoes mechanical ventilation must be diagnosed as quickly as possible and treated.