Respiratory Failure Health Article

Definition

Respiratory failure occurs when the lungs' ability to either add oxygen to the bloodstream or remove carbon dioxide from it is impaired. Respiratory failure can have any one of several causes, such as lung disease or infection, electrolyte imbalance, interruption of the nerve signals that regulate breathing or nervous system damage, structural (rib cage) collapse, or airway obstruction.

Description

During respiration, the lungs extract oxygen from inhaled air, oxygenate the bloodstream, and eliminate carbon dioxide (CO₂) from the blood into exhaled air. In respiratory failure, the level of oxygen in the blood becomes dangerously low, and/or the level of CO₂ becomes dangerously high. This result can happen if the gas-exchange process breaks down or if ventilation is inhibited.

There are two main types of respiratory failure. Hypoxemic failure occurs when normal gas exchange is interrupted, causing a condition called hypoxemia. When this happens, there is too little oxygen in the blood, and all of the body's organs and tissues suffer as a result. One common type of hypoxemic respiratory failure, which occurs in both adults and premature infants, is respiratory distress syndrome, a condition in which fluid or tissue changes or physical immaturity prevent oxygen from passing out of the lungs' air sacs into the circulating blood. Hypoxemia is also caused by exposure to high altitudes, where there is less oxygen in the air; lung diseases that impair the transfer of oxygen into the blood through the alveolar capillaries; severe anemia; and blood vessel disorders that shunt blood away from the lungs, thus preventing the lungs from picking up oxygen.

Ventilatory failure occurs when the body cannot exhale CO₂ properly. The resulting buildup in the blood is called hypercapnia. Ventilatory failure can result when the respiratory center in the brainstem fails to drive breathing, when muscle disease prevents the chest wall from expanding during inhalation, or when a patient has chronic obstructive pulmonary disease that impairs exhalation. Many of the diseases and conditions that produce respiratory failure can cause both hypoxemia and hypercapnia simultaneously.

Causes and symptoms

Respiratory failure can have a variety of causes; all of them inhibit breathing in some way.

• Airway obstructions: chronic bronchitis with heavy secretions, emphysema, cystic fibrosis, asthma, and obstructive sleep apnea, in which patients stop breathing for short periods during sleep.
• Depressed respiration: weakened breathing that is caused by drug abuse (especially narcotics or opiates) and/or alcohol intoxication, both of which depress the respiratory center. Extreme obesity can also be a factor, because it restricts chest wall expansion during inhalation, diminishing the body's ability to acquire enough oxygen.
• Muscle weakness: this can be caused by such neuromuscular diseases as myasthenia gravis, muscular dystrophy, multiple sclerosis, polio, and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease), as well as strokes that paralyze respiratory muscles and spinal cord injuries.
• Lung diseases and disorders: severe pneumonia, respiratory distress syndrome, pulmonary fibrosis and other scarring diseases of the lung, radiation exposure, burn injury from smoke inhalation, and widespread lung cancer. Pulmonary edema, often a result of heart disease, can also cause respiratory failure.
• Chest wall abnormalities: these can be caused by scoliosis or severe thoracic injuries, including trauma to the phrenic nerve, which supplies the lungs and diaphragm.
• Cellular disorders: any interruption of the Krebs cycle can impede respiration, as can such electrolyte disorders as hypokalemia.

Patients with respiratory failure often have a rapid, weak, or shallow pulse; they are also usually short of breath, restless, and may become confused and disoriented when normal blood gas levels are altered. High blood CO₂ levels can cause headaches and, in time, a semi-conscious state, or even coma. Low blood oxygen causes cyanosis, and can produce arrhythmias. Lung disease may cause abnormal breath sounds that are audible through a stethoscope: wheezing in asthma, rales in pneumonia, or distant breath sounds in obstructive lung disease. A patient with ventilatory failure is prone to gasp for breath, and may use the neck and shoulder muscles to help expand the chest.

Diagnosis

The signs and symptoms of respiratory failure depend on the underlying condition causing it. The key to diagnosis and treatment is measuring the levels of oxygen, carbon dioxide, and acid in the blood at regular intervals. Generally, laboratory technologists and respiratory therapists perform all needed blood work and lung-function testing.