Chronic Hypoxemia in Pediatrics
Hypoxemia is a condition from which there is a low level of partial pressure of oxygen in the arterial blood. Blood oxygen level is measured by an arterial blood test or through a pulse oximeter. Normal blood oxygen readings are between 95 to 100 percent, values under 90 percent are considered low. Severe hypoxemia occurs when oxygen saturation drops below 80 percent.
Causes of Hypoxemia
The oxygen that is inhaled passes from the air sacs in the lungs and through tiny blood vessels (capillaries) in the air sac walls. It enters the bloodstream and is distributed throughout the body. Anything that interferes with this process can cause low blood oxygen.
Hypoxemia is usually precipitated by respiratory disorders. Additionally, hypoxemia may also occur as a result of one or a combination of the following:
- Hypoventilation- the oxygen content in the blood is decreased and there is a marked increase in the levels of carbon dioxide
- Low Inspired Oxygen- the fraction of inspired oxygen (FIO2) in the blood is decreased
- Left to right shunt- a condition when there is a transfer of blood from the left side of the heart to its right side. This may occur as a result of a hole in the following walls: the arterial walls, the wall separating the two upper chambers (left and right atrium) or the wall separating the two lower chambers (left and right ventricles) of the heart.
- Ventilation-Perfusion mismatch- an imbalance between the volume of gas expired by the alveoli (alveolar ventilation) and the pulmonary capillary blood flow
- Diffusion Impairment- a marked reduction or restriction of oxygen movement from the alveoli to capillaries.
Signs and Symptoms
- Symptoms of mild hypoxemia:
- Shortness of breath
- Disorientation, confusion, lassitude and listlessness
- Symptoms of severe hypoxemia:
- Cyanosis – bluish discoloration of the skin
- Cheyne-Stokes respiration – alternating periods of shallow and deep breathing with episodes of apnea
- Increased blood pressure
- Apnea – temporary cessation of breathing
- Tachycardia, Hypotension
- Ventricular fibrillation – irregular and uncoordinated contractions of the ventricles
- Polycythemia – abnormal increase in RBCs
- Cardiac arrest, Coma
Children’s Response to Chronic Hypoxemia
- Persistent hypoxemia may elicit an increased production of red blood cells to compensate for the low levels of oxygen. This increase is mediated by the increased levels of erythropoietin by the kidneys in response to low oxygen levels in the blood. This may lead to secondary polycythemia.
- To compensate for chronic hypoxemia, the child generally goes into constant tachycardia, leading to congestive heart failure. Tachycardia is the hypoxemic body’s response in an attempt to increase perfusion by increasing cardiac output or it may be due to increased catecholamine activity from the adrenal medulla in response to the stress of hypoxemia.
Image by: normalbreathing.com