Physicians and other health care providers refer to a number of different indications for intubation when deciding whether to provide breathing assistance. Patients who are unable to keep an open airway are often intubated to maintain the ability of air to reach the lungs, and for the expired air to be released into the environment. Another indication for intubation is having a problem in getting enough oxygen from the inspired air into the blood. Similarly, if patients are unable to expire enough carbon dioxide, they are also intubated.
One of the common indications for intubation is to protect the airway. Some patients without the cognitive function required to keep their airways open could allow the airway to clog with stomach contents that have been vomited. For this reason, patients who are under general anesthesia, who are intoxicated with a number of different substances, or who have a variety of brain disorders are intubated to make sure that the lung continues to receive an uninterrupted flow of air. Patients who might be bleeding into the airway are also intubated to protect the airway, as the accumulating blood could block the passage of air.
Another one of the common indications for intubation is a failure of the blood to obtain enough oxygen from the lungs. This can occur as a result of a number of pathologic processes, including pneumonia, pulmonary embolism, and diseases that destroy the lung tissue. Whereas the air present in the environment contains less than 30% oxygen, a ventilator can pump gas containing 100% oxygen into the intubated patient. With the higher oxygen content present in the lungs, the blood is able to pick up more oxygen to distribute to the rest of the body.
Patients are also considered to have one of the indications for intubation if they cannot get rid of enough carbon dioxide gas, a waste product of metabolism that is typically released through the process of expiration. This can occur as a result of a number of different conditions, including chronic obstructive pulmonary disease (COPD) and severe asthma attacks. It can also occur as a result of metabolic abnormalities that increase the acidity of the blood.
Sometimes, patients who are obtaining enough oxygen through inspiration and getting rid of enough carbon dioxide via expiration are still intubated in order to further decrease the release of carbon dioxide from the body. This is considered one of the indications for intubation in patients who have an increased intracranial pressure. By increasing the rate of breathing, more carbon dioxide is expelled. The resulting decreased concentration of carbon dioxide present in the blood decreases the diameter of the blood vessels in the brain, and therefore decreases the pressure inside the brain.