Respiratory failure develops when the lungs and respiratory system become unable to provide the body with sufficient oxygen (O2) and fail to excrete or “blow off ” accumulated carbon dioxide (CO2). When the major disturbance is primarily an inability of the respiratory system to meet the body’s oxygen (O2) requirements, then hypoxemic respiratory failure is present. When CO2 and acid levels rise within the body because the lungs are unable to keep up their excretory function, then hypercarbic respiratory failure occurs. A mixed hypoxemic and hypercarbic pattern may exist.
Respiratory failure can be very gradual, and it may develop and progress slowly over time, from months to years, as in the case of chronic respiratory failure. Progressive cigarette-related emphysema is one example of a cause of gradual respiratory insufficiency that may, with time, continue on to respiratory failure. Asthma is not typically a cause of chronic respiratory failure. Acute respiratory failure, as the name implies, occurs rapidly over a period of hours to days.
Fatal or near-fatal asthma, thankfully rare events, are both causes of acute respiratory failure. In either situation, acute or chronic, there comes a point where the respiratory failure becomes so marked that the body will become deprived of adequate oxygen and be subjected to dangerously rising levels of carbon dioxide and acids. Sampling of arterial blood gases (ABGs) in fatal and near-fatal asthma, for example, show low values of oxy-gen (the PaO2 value is <60 mmHg) and rising levels of carbon dioxide (the PaCO2 value rises above 41 mmHg).
As the lungs no longer function effectively and fail, other organs will begin to fail in response. The brain, in particular, is very sensitive to low oxygen levels, as well as to elevations in carbon dioxide values, each of which are harmful separately. As the oxygen and carbon dioxide levels become more abnormal, consciousness becomes impaired. Coma and death will ensue. An individual with progressive respiratory failure is usually critically ill and in danger of death without aggressive medical intervention and life support, as reviewed in more detail in endotracheal intubation.