What is respiratory failure?
Respiratory failure means the respiratory system is not performing gas exchange in an appropriate way. It can mean that one or both gas exchange processes have failed- oxygenation and/or carbon dioxide elimination.
Respiratory failure is defined as PaO2 value of less than 60 mm Hg or PaCO2 value of more than 50 mm Hg.
Classification of respiratory failure includes hypoxemic or hypercapnic failure. It can also be acute or chronic.
Hypoxemic respiratory failure with PaO2 of 60 mm Hg or less, while PaCO2 is normal, is the most common form of respiratory failure. It can be seen in almost all the acute diseases of the lungs, with fluid filling or alveolar collapse. Pulmonary edema, pneumonia and pulmonary hemorrhage are some of the hypoxemic respiratory failure.
Hypercapnic respiratory failure means that PaCO2 values are higher than 50 mm Hg. Hypoxemia is often seen in patients with hypercapnic respiratory failure, especially if they are breathing indoor air. This type of respiratory failure is seen in people suffering from drug overdose, chest wall abnormalities, diseases affecting neuromuscular system, but also from asthma and chronic obstructive pulmonary disease.
As for the causes, this disorder can result from many different diseases and conditions, involving problems with central nervous system, spinal cord and nerves, muscles, lungs, airways, blood stream and others.
Acute and chronic respiratory failure
Acute respiratory failure sets in quickly, over the course of several minutes or several hours. The pH levels in acute form of this disorder are less than 7.3, because of the sudden onset. On the other hand, in chronic respiratory failure, which develops over an extended period of time, the kidneys have time to adapt and compensate so the pH levels are only slightly decreased.
It may be difficult to tell the difference between acute and chronic respiratory failure basing only on the value of arterial blood gasses. Certain clinical markers are helpful in diagnosing chronic hypoxemia, such as cor pulmonale and polycythemia.
Signs and symptoms of acute respiratory failure
A person suffering from acute respiratory failure will try to breathe normally by adopting a characteristic posture, for example sitting forward, possibly with drooling, eyes closed and all the muscles participating in respiration fully engaged. Anxiety and preoccupation with breathing are also very common.
Acute respiratory failure affect the central nervous system and cardiovascular system, causing confusion and drunk-like state, bradycardia and cyanosis in hypoxia, and tremor, rapid pulse, redness and blood pressure changes in hypercapnia.