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Respiratory Failure

Definition

Respiratory failure is nearly any condition that affects breathing function or the lungs themselves and can result in failure of the lungs to function properly. The main tasks of the lungs and chest are to get oxygen from the air that is inhaled into the bloodstream, and, at the same to time, to eliminate carbon dioxide (CO₂) from the blood through air that is breathed out. In respiratory failure, the level of oxygen in the blood becomes dangerously low, and/or the level of CO₂ becomes dangerously high. There are two ways in which this can happen. Either the process by which oxygen and CO₂ are exchanged between the blood and the air spaces of the lungs (a process called "gas exchange") breaks down, or the movement of air in and out of the lungs (ventilation) does not take place properly.

Description

Respiratory failure often is divided into two main types. One of them, called hypoxemic respiratory failure, occurs when something interferes with normal gas exchange. Too little oxygen gets into the blood (hypoxemia), and all organs and tissues in the body suffer as a result. One common type of hypoxemic failure, occurring in both adults and prematurely born infants, is respiratory distress syndrome, a condition in which fluid or tissue changes prevent oxygen from passing out of the air sacs of the lungs into the circulating blood. Hypoxemia also may result from spending time at high altitudes (where there is less oxygen in the air); various forms of lung disease that separate oxygen from blood in the lungs; severe anemia ("low blood"); and blood vessel disorders that shunt blood away from the lungs, thus precluding the lungs from picking up oxygen.

The other main type of respiratory failure is ventilatory failure, occurring when, for any reason, breathing is not strong enough to rid the body of CO₂. Then CO₂ builds up in the blood (hypercapnia). Ventilatory failure can result when the respiratory center in the brainstem fails to drive breathing; when muscle disease keeps the chest wall from expanding when breathing in; or when a patient has chronic obstructive lung disease that makes it very difficult to exhale air with its CO₂. Many of the specific diseases and conditions that cause respiratory failure cause both too little oxygen in the blood (hypoxemia) and abnormal ventilation.

Causes and symptoms

Several different abnormalities of breathing function can cause respiratory failure. The major categories, with specific examples of each, are:

Obstruction of the airways. Examples are chronic bronchitis with heavy secretions; emphysema; cystic fibrosis; asthma (a condition in which it is very hard to get air in and out through narrowed breathing tubes).
Weak breathing. This can be caused by drugs or alcohol, which depress the respiratory center; extreme obesity; or sleep apnea, where patients stop breathing for long periods while sleeping.
Muscle weakness. This can be caused by a muscle disease called myasthenia; muscular dystrophy; polio; a stroke that paralyzes the respiratory muscles; injury of the spinal cord; or Lou Gehrig's disease.
Lung diseases, including severe pneumonia. Pulmonary edema, or fluid in the lungs, can be the source of respiratory failure. Also, it can often be a result of heart disease; respiratory distress syndrome; pulmonary fibrosis and other scarring diseases of the lung; radiation exposure; burn injury when smoke is inhaled; and widespread lung cancer.
An abnormal chest wall (a condition that can be caused by scoliosis or severe injury of the chest wall).

A majority of patients with respiratory failure are short of breath. Both low oxygen and high carbon dioxide can impair mental functions. Patients may become confused and disoriented and find it impossible to carry out their normal activities or do their work. Marked CO₂ excess can cause headaches and, in time, a semi-conscious state, or even coma. Low blood oxygen causes the skin to take on a bluish tinge. It also can cause an abnormal heart rhythm (arrhythmia). Physical examination may show a patient who is breathing rapidly, is restless, and has a rapid pulse. Lung disease may cause abnormal sounds heard when listening to the chest with a stethoscope: wheezing in asthma, "crackles" in obstructive lung disease. A patient with ventilatory failure is prone to gasp for breath, and may use the neck muscles to help expand the chest.

Diagnosis

The symptoms and signs of respiratory failure are not specific. Rather, they depend on what is causing the failure and on the patient's condition before it developed. Good general health and some degree of "reserve" lung function will help see a patient through an episode of respiratory failure. The key diagnostic determination is to measure the amount of oxygen, carbon dioxide, and acid in the blood at regular intervals. A sudden low oxygen level in the lung tissue may cause the arteries of the lungs to narrow. This, in turn, causes the resistance in these vessels to increase, which can be measured using a special catheter. A high blood level of CO₂ may cause increased pressure in the fluid surrounding the brain and spinal cord; this, too, can be measured.

Treatment

Nearly all patients are given oxygen as the first treatment. Then the underlying cause of respiratory failure must be treated. For example, antibiotics are used to fight a lung infection, or, for an asthmatic patient, a drug to open up the airways is commonly prescribed.

A patient whose breathing remains very poor will require a ventilator to aid breathing. A plastic tube is placed through the nose or mouth into the windpipe and is attached to a machine that forces air into the lungs. This can be a lifesaving treatment and should be continued until the patient's own lungs can take over the work of breathing. It is very important to use no more pressure than is necessary to provide sufficient oxygen; otherwise ventilation may cause further lung damage. Drugs are given to keep the patient calm, and the amount of fluid in the body is carefully adjusted so that the heart and lungs can function as normally as possible. Steroids, which combat inflammation, may sometimes be helpful but they can cause complications, including weakening the breathing muscles.

The respiratory therapist has a number of methods available to help patients overcome respiratory failure. They include:

Suctioning the lungs through a small plastic tube passed through the nose, in order to remove secretions from the airways that the patient cannot cough up.
Postural drainage, in which the patient is propped up at an angle or tilted to help secretions drain out of the lungs. The therapist may clap the patient on the chest or back to loosen the secretions, or a vibrator may be used for the same purpose.
Breathing exercises often are prescribed after the patient recovers. They make the patient feel better and help to strengthen the muscles that aid breathing. One useful method is for the patient to suck on a tube attached to a clear plastic hosing containing a ball so as to keep the ball lifted. Regular deep breathing exercises are simpler and often just as helpful. Another technique is to have the patient breathe out against pursed lips to increase pressure in the airways and keep them from collapsing.

Prognosis

The outlook for patients with respiratory failure depends chiefly on its cause. If the underlying disease can be effectively treated, with the patient's breathing supported in the meantime, the outlook is usually good.

Care is needed not to expose the patient to polluting substances in the atmosphere while recovering from respiratory failure; this could tip the balance against recovery. When respiratory failure develops slowly, pressure may build up in the lung's blood vessels, a condition called pulmonary hypertension. This condition may damage the vessels, worsen hypoxemia, and cause the heart to fail. If it is not possible to provide enough oxygen to the body, complications involving either the brain or the heart may prove fatal.

If the kidneys fail or the diseased lungs become infected, the prognosis is worse. In some cases, the primary disease causing the lungs to fail is irreversible. The patient, family, and physician together then must decide whether to prolong life by ventilator support. Occasionally, lung transplantation is a possibility, but it is a highly complex procedure and is not widely available

Prevention

Because respiratory failure is not a disease itself, but the end result of many lung disorders, the best prevention is to treat any lung disease promptly and effectively. It is also important to make sure that any patient who has had lung disease is promptly treated for any respiratory infection (even of the upper respiratory tract). Patients with lung problems should also avoid exposure to pollutants, as much as is possible. Once respiratory failure is present, it is best for a patient to receive treatment in an intensive care unit, where specialized personnel and all the needed equipment are available. Close supervision of treatment, especially mechanical ventilation, will help minimize complications that would compound the problem.

Resources

Organizations

National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. http://www.nhlbi.nih.gov.

National Respiratory Distress Syndrome Foundation. P.O. Box 723, Montgomeryville, PA 18936.

Key terms

Chronic obstructive lung disease — A common form of lung disease in which breathing, and therefore gas exchange, is labored and increasingly difficult.

Gas exchange — The process by which oxygen is extracted from inhaled air into the bloodstream, and, at the same time, carbon dioxide is eliminated from the blood and exhaled.

Hypoxemia — An abnormally low amount of oxygen in the blood, the major consequence of respiratory failure, when the lungs no longer are able to perform their chief function of gas exchange.

Pulmonary fibrosis — An end result of many forms of lung disease (especially chronic inflammatory conditions). Normal lung tissue is converted to scarred, "fibrotic" tissue that cannot carry out gas exchange.

respiratory failure

An acute or chronic condition in which pulmonary function is markedly impaired, usually characterized by elevated carbon dioxide or decreased oxygen (or both) in the arterial blood. Patients in respiratory failure often require ventilators to breathe.

respiratory failure,

the inability of the cardiovascular and pulmonary systems to maintain an adequate exchange of oxygen and carbon dioxide in the lungs. Respiratory failure may be caused by a failure in oxygenation or in ventilation. Oxygenation failure is characterized by refractory hypoxemia and occurs in diseases that affect the alveoli or interstitial tissues of the lungs, such as alveolar edema, emphysema, fungal infections, leukemia, lobar pneumonia, lung carcinoma, various pneumoconioses, pulmonary eosinophilia, sarcoidosis, or tuberculosis. Ventilatory failure, characterized by increased arterial tension of carbon dioxide, occurs in acute conditions in which retained pulmonary secretions cause increased airway resistance and decreased lung compliance, as in bronchitis. Ventilation may also be reduced by depression of the respiratory center by barbiturates or opiates, hypoxia, hypercapnia, intracranial diseases, trauma, or lesions of the neuromuscular system or thoracic cage. Respiratory failure in preexisting chronic lung diseases may be precipitated by added stress, as with cardiac failure, surgery, anesthesia, or respiratory tract infections. Treatment of respiratory failure includes clearing the airways by suction, bronchodilators, or tracheostomy or endotracheal tube with ventilator support; antibiotics for infections that are usually present; anticoagulants for pulmonary thromboemboli; and electrolyte replacement in fluid imbalance. Oxygen may be administered in some cases; in others it may further decrease the respiratory reflex by removing the stimulus of a decreased level of oxygen. Chronic respiratory failure may result in cor pulmonale with congestive heart failure and respiratory acidosis. See also acute respiratory failures, airway obstruction, carbon dioxide, hypercapnia, hyperventilation, hypoxemia, hypoxia, respiratory acidosis.

respiratory failure,

n a condition in which the level of oxygen in the blood is too low and the level of carbon dioxide is too high. This condition may be life threatening.

failure

inability to perform or to function properly.

failure to conceive

said of cows which return to estrus after mating.

kidney failure

see renal failure.

failure of passive transfer

see maternal immunity.

respiratory failure

called also ventilatory failure; see respiratory failure.

failure to thrive

used generally to describe young animals which are not gaining weight or growing; can be due to disease or management problems. In llamas, used to describe a specific syndrome in which the young are normal in early age, but later stop growing. Rickets is one possible cause, but there may be others.

respiratory

pertaining to respiration. See also pulmonary.

acute respiratory disease of turkeys

see turkey coryza.

acute respiratory distress syndrome

a noncardiogenic pulmonary edema characterized by disruption of pulmonary capillary endothelium and accumulation of high-protein edema fluid in the lungs. See also shock lung, atypical interstitial pneumonia, neonatal maladjustment syndrome.

respiratory arrest

sudden complete cessation of respiratory movement.

respiratory burst of neutrophils

the series of biochemical reactions that take place within a neutrophil when a particle is phagocytosed. Important in the host defense mechanisms.

respiratory centers

see respiratory centers.

chronic respiratory disease

see chronic respiratory disease.

respiratory cilia

see cilia.

respiratory clearance

clearance of inhaled particles from the respiratory system by absorption of finally solubilized material through the respiratory epithelium, passage through the alveolar epithelium at special sites near the alveolar ducts, or to the exterior by a flow of alveolar fluid to the bronchi, a moving sheet of mucus into the bronchioles, up the bronchioles, bronchi and trachea with the assistance of repiratory cilia to the pharynx.

respiratory control

quantitative relationship between oxidative phosphorylation and electron transfer. Traditionally presented as a P/O ratio indicating the number of ATP molecules synthesized per atom of oxygen consumed.

respiratory control ratio

ratio of oxygen uptake in the presence of ADP to that in the absence of ADP. Used as an index of the functional integrity of prepared mitochondria since it is above 10 in good preparation and unity in aged or damaged mitochondria.

respiratory cycle

the cycle of inspiration, expiration, pause of the normal resting cycle depends on sensors in the respiratory system which provide stimuli to initiate the next part of the cycle.

respiratory dead space

see dead space (2).

respiratory depression

the rate and/or depth of respiration are insufficient to maintain adequate gas exchange in the lungs; a subjective judgment tending to be superseded, at least during anesthesia, by instrumentation. See respiration monitors.

respiratory depth

amplitude of each respiratory movement.

respiratory difficulty

see dyspnea.

respiratory disease pattern

may be aerogenous when the pathogen is inhaled or hematogenous when the pathogen is delivered to the lungs in the blood supply.

respiratory distress syndrome of newborn (RDS)

see hyaline membrane disease.

respiratory exchange ratio

the carbon dioxide output divided by the oxygen uptake; see also respiratory quotient (below).

respiratory failure

a life-threatening condition in which respiratory function is inadequate to maintain the body's need for oxygen supply and carbon dioxide removal while at rest; called also acute ventilatory failure. The type of failure varies with the CO₂ content of the blood and may be asphyxial, when there is gasping, dyspneic when there is dyspnea, paralytic when the respiratory movements gradually fade away, tachypneic when the movements are fast and shallow.

respiratory grunting

grunting at the peak of each inspiration, or on percussion of the chest wall; indicates pain in the pleura.

respiratory insufficiency

a condition in which respiratory function is inadequate to meet the body's needs when increased physical activity places extra demands on it. Insufficiency occurs as a result of progressive degenerative changes in the alveolar structure and the capillary tissues in the pulmonary bed.

respiratory noises

includes sneezing, snorting, stridor, stertor (snoring), wheezing, roaring, grunting.

respiratory paralysis

see respiratory failure (above).

respiratory quotient (RQ)

the ratio of the volume of expired carbon dioxide to the volume of oxygen absorbed by the lungs per unit of time. Called also respiratory exchange ratio (above).

respiratory rate

the number of respirations per minute. Normal rates per minute are: horses 8 to 10; cattle 10 to 30; sheep and pigs 10 to 20; goats 25 to 35; dogs 10 to 30; cats 20 to 30.

respiratory rhythm

normally consists of three phase cycles of inspiration, expiration, pause; prolongation of inspiration suggests obstruction of the upper respiratory tract, prolongation of expiration, or a double respiratory effort suggests loss of recoil elasticity of the lungs. See also biot's respirations, cheyne-stokes respiration.

respiratory secretion

includes samples collected by nasal swab, nasopharyngeal swab, percutaneous tracheobronchial lavage and fiberoptic endoscopic sampling. Assessment is by laboratory examination for cellular content, bacteria, viruses, helminth parasites, fungi.

respiratory system

the group of specialized organs whose specific function is to provide for the transfer of oxygen from the air to the blood and of waste carbon dioxide from the blood to the air. These functions are performed by the tubular and cavernous organs which allow atmospheric air to reach the membranes across which gases are exchanged with the blood. The system includes the organs of the respiratory tract (below) plus the respiratory centers in the medulla. The supportive roles of the nervous system, the muscular, cardiovascular and hemopoietic systems are also essential.

respiratory tract

the organs of the tract include the upper respiratory tract of the nasal cavities, the pharynx, larynx, trachea and bronchi, and the lower respiratory tract comprising the bronchioles and alveoli of the lungs.

respiratory viruses

see Table 8.2.