Pulmonary shunt is a respiratory problem where gas exchange fails to take place in the lungs, leading to low oxygen levels in the blood. This can cause problems for the patient, as lack of oxygen will injure organs and tissues. Most commonly, patients experience pulmonary shunt as a symptom of a larger respiratory problem. To treat it, doctors must determine the origins of the issue and treat them to increase the blood oxygen level.
In patients with pulmonary shunt, blood can reach the lungs successfully and the alveoli, the tiny air sacks in the lungs, are fully perfused with blood. Oxygen, however, does not enter the blood in the normal gas exchange process where carbon dioxide leaves the blood and oxygen replaces it. As a result, blood passes through the pulmonary artery, fails to pick up oxygen, and enters the pulmonary vein to return to the heart. The heart pumps the blood through the body, but it is not carrying enough oxygen, and the patient's tissues will start to experience hypoxia.
Doctors can determine the severity of the problem by calculating the shunt fraction, a reflection of much blood the heart is pumping without any oxygen. Usually, only part of the lung is involved and blood is picking up oxygen from other alveoli, providing some for the cells to use, but not enough for the patient to be healthy. It is normal for a small percentage of the blood to not carry oxygen, usually around five percent, but having low oxygen saturation can be very dangerous.
A common cause of pulmonary shunt is pulmonary edema, where fluid appears in and around the lungs and interferes with gas exchange. People commonly experience this issue during heart failure, when the heart cannot circulate blood effectively and patients may become very ill. Severe pneumonia and bronchitis can also cause pulmonary shunt by filling the lungs with fluids like mucus.
When a patient's oxygen saturation is low, a doctor may decide to put the patient on supplemental oxygen, increasing the chance of successful gas exchange. Doctors may also pursue other measures like medications, procedures to remove fluid from the lungs, and treating underlying heart failure and related conditions. If the patient does not receive treatment, death is an eventual possibility, as the organs will start to shut down due to hypoxia, and patients will be more vulnerable to infection and other complications as a result of their ill health.