Acute respiratory failure can be caused by various factors that affect gas exchange in the lungs, resulting in high levels of carbon dioxide or low levels of oxygen in the blood. Causes are classified as hypoxemic or hypercapnic, with lung diseases and injuries being common culprits.
Acute respiratory failure can be caused by anything that causes inadequate gas exchange in the lungs. When a person breathes, carbon dioxide (CO2) is absorbed into the bloodstream from the lungs and oxygen is absorbed into the blood; inadequate gas exchange causes high levels of carbon dioxide or low levels of oxygen in the blood. “Acute” refers to an imbalance that develops very quickly, anywhere from a few minutes to an hour. Acute respiratory failure can be caused by an injury, illness, or blood flow problems.
Causes of acute respiratory failure are classified as hypoxemic or hypercapnic. Hypoxemic failure, known as type 1 respiratory failure, refers to causes that reduce the amount of oxygen in the blood at pressures below 60 millimeters of mercury (mmHg). Normal blood oxygen pressure ranges from 85 to 100 mmHg. The main causes of hypoxemic acute respiratory failure are bleeding or fluid accumulation in the lungs.
Hypercapnic or type 2 respiratory failure is due to a buildup of carbon dioxide in the blood. Normal blood carbon dioxide pressure ranges from 35 to 45 mmHg; hypercapnic levels are higher, above 50 mmHg. The main causes of hypercapnic acute respiratory failure include loss of consciousness, lung disease, and hypoventilation or low respiratory rate.
Several types of lung disease can cause both type 1 and type 2 acute respiratory failure. Pneumonia and cystic fibrosis cause the lungs to fill with fluid. Emphysema and severe asthma can cause CO2 to build up when the lungs or lung cells become blocked. In each of these conditions, blood oxygen levels are reduced and CO2 cannot be released from the blood.
Conditions that limit blood flow to the lungs, such as pulmonary embolism, also result in inadequate gas exchange. A pulmonary embolism is a blockage of the pulmonary arteries so that blood cannot reach the lung cells to exchange carbon dioxide for new oxygen. High levels of carbon dioxide build up in the bloodstream, eventually reaching levels high enough for respiratory failure.
Injuries to specific parts of the body can cause both hypocapnic and hypoxemic insufficiency. A severe blow to the head or an alcohol or drug overdose can alter the brain functions that control the lungs, causing the breathing rate to decrease. A strong blow to the chest can injure ribs or lung tissue, causing improper breathing. If a broken rib punctures the lung, acute respiratory failure can occur due to the bleeding.
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