What is refractory hypoxemia?

Hypoxemia is a condition in which the oxygen levels in the blood are too low. Refractory hypoxemia is rare and refers to hypoxemia that cannot be corrected by giving the patient additional oxygen to breathe. It usually develops as the end result of a condition known as adult respiratory distress syndrome, in which breathing becomes extremely difficult. Various techniques have been tried to treat refractory hypoxemia, but no really effective therapies have been found. Hypoxemia is a form of hypoxia, which is a more general term used to describe low oxygen levels in any part of the body, including the tissues and blood.

There are numerous causes of hypoxemia including anemia, high altitude, and an obstructed airway. The most common causes leading to respiratory distress syndrome, which is associated with hypoxemia, are pneumonia or an infection that overwhelms the entire body. Hypoxemia can usually be improved by giving patients oxygen, but refractory hypoxemia does not respond to this treatment.

Refractory hypoxemia often occurs because the air spaces within the lungs are filled with fluid. This could be the result of bleeding in the lungs, infection, or heart failure. As the air spaces fill with fluid, this prevents inhaled oxygen from passing through the blood vessels lining the lung spaces and entering the bloodstream. In this situation, despite administering oxygen, blood oxygen levels remain abnormally low.

Signs of hypoxemia include increased dyspnea, confusion, and loss of consciousness. If the lungs are filled with fluid, doctors may hear characteristic crackling noises when listening to the chest through a stethoscope. Refractory hypoxemia is diagnosed when blood oxygen levels do not improve after treating hypoxemia with therapies such as supplemental oxygen and mechanical ventilation.

Several potentially beneficial treatments for refractory hypoxemia have been tried. These include patients lying on their fronts, using special ventilation techniques where smaller than normal volumes of air are delivered at a faster rate, and administering medications that dilate blood vessels in the lungs. Lying patients on their fronts is believed to aid breathing by allowing air spaces to open in the lungs. In another treatment, blood is pumped out of the body through an artificial lung to increase oxygen levels, before returning to the patient. Unfortunately, none of the therapies tested have shown a significant improvement in survival rates for patients with refractory hypoxemia.

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