Hypoxia refers to a insufficient oxygenation of the tissues and is of course dangerous. We will start by first discussing some basics about oxygen and then review common causes of tissue hypoxia. The goal of a portable oxygen machine is to prevent this deadly condition.
What is oxygen?
Oxygen is a gas that we breathe everyday and is about 20% of the atmosphere (most of the rest is Nitrogen). Oxygen is an electron acceptor and drives the pathway that produces energy (ATP) that our cells use. Lack of oxygen results in the hypoxia.
What causes tissue hypoxia?
We can divide tissue hypoxia into three main categories: ischemia, hypoxemia, and hemoglobin related abnormalities.
Ischemia is when there is a decrease in arterial blood flow and includes examples such as atherosclerosis of the coronary arteries (which can lead to a heart attack). So, when the coronary artery is blocked, not enough blood will flow to provide the oxygen that the heart needs. This will result in Ischemia, a type of hypoxia.
Hypoxemia is a decrease in the arterial Oxygen content. In this case, the flow may be ok but there is not enough oxygen being supplied. Cause of this can be respiratory acidosis, ventilation defects, perfusion defects, and diffusion defects. Respiratory acidosis is when there is a retention of carbon dioxide in the lungs. Ventilation defects result when there is impaired oxygen delivery to the lungs (giving oxygen by a portable oxygen machine will not help such a patient). Perfusion defects arise when there is an absence of blood flow to the alveoli. Diffusion defects result when the oxygen cannot move from across the capillary walls between the air and the blood.
Hemoglobin related abnormalities that cause hypoxia include anemia, methemoglobinemia, carbon monoxide poisoning, and cyanide poisoning.
Role of Oxygen Machines?
Portable oxygen is only useful in some types of hypoxia such as in certain hypoxemias. In many cases such as in ischemia or poisoning, oxygen benefits may be very limited.