Our body needs oxygen to carry out the functions like cellular respiration and energy metabolism which are essential for its survival. One is therefore most likely to experience distressing symptoms in event of a decrease in the levels of oxygen. The term 'hypoxemia' refers to a medical condition that is characterized by a decrease in the partial pressure of oxygen in the arterial blood (PaO2). PaO2 is measured in millimeters of mercury (mm Hg or Torr). It refers to the pressure exerted by oxygen in a mixture of other gases. Arterial Blood Gas (ABG) testing helps measure PaO2.
Though these medical conditions are in some way related to reduction in the levels of oxygen in the body, these are distinct medical conditions. Here's some information that will help you distinguish hypoxemia from the rest of the aforementioned conditions.
What is Hypoxemia?
This condition occurs when the pulmonary alveoli (microscopic sacs in lungs where exchange of oxygen and carbon dioxide takes place) are starved of oxygen. In this condition, a substantial decrease is observed in the levels of partial pressure of arterial oxygen. Under normal circumstances, partial pressure of oxygen in arterial blood should be within 95 to 100 mmHg. When the partial pressure of arterial oxygen in the blood falls below 80 mmHg, one is diagnosed with severe hypoxemia.
Also referred to as oxygen desaturation, hypoxemia should not be confused with medical conditions such as anoxia, asphyxia, hypoxia or anemia. Hypoxemia refers to a condition that is characterized by low oxygen content and low partial pressure of oxygen in arterial blood. The term 'hypoxia' refers to the deficiency of oxygen in the body as a whole or in some specific part of the body. 'Asphyxia' is a condition that is characterized by the absence of oxygen along with the accumulation of carbon dioxide. 'Anoxia' refers to the absence of oxygen in the body tissues or in the arterial blood. This implies extremely low levels of oxygen in the body. 'Anemia'is another medical condition that is characterized by a decrease in the number of red blood cells or low levels of hemoglobin in the blood. While the oxygen content in the arterial blood is low in people who are anemic, the partial pressure of oxygen in the arterial blood doesn't decrease.
Arterial Oxygen Content
The arterial oxygen content can be calculated with the help of the following equation:
Arterial Oxygen Content = (Hgb x 1.36 x SaO2) + (0.0031 x PaO2)
In the equation given above, Hgb stands for the hemoglobin, SaO2 is the percentage of hemoglobin saturated with oxygen and (PaO2) refers to the partial pressure of arterial oxygen.
The symptoms of hypoxemia will vary depending on the extent to which the partial pressure has fallen.
Symptoms of Mild Hypoxemia
- Disorientation, confusion, lassitude, and listlessness
- Cyanosis (Skin appearing bluish due to insufficient oxygen)
- Cheyne-Stokes respiration (irregular pattern of breathing)
- Elevated blood pressure
- Apnea (temporary cessation of breathing)
- Tachycardia (increased rate of heartbeat, more than 100 per minute)
- Hypotension (abnormally low blood pressure, below 100 diastolic and 40 systolic. Here, as an effect of an initial increase in cardiac output and rapid decrease later.)
- Ventricular fibrillation (irregular and uncoordinated contractions of the ventricles)
- Asystole (severe form of cardiac arrest, heart stops beating)
- Polycythemia (abnormal increase in the number of red blood cells. The bone marrow may be stimulated to produce excessive RBCs in case of patients suffering from chronic hypoxemia)
Hypoxemia is usually triggered off by respiratory disorders.
- Chronic obstructive pulmonary disease (COPD)
- Airway obstruction
- Acute respiratory distress syndrome
- Pneumothorax (collapsed lung)
- Congenital heart defects
- Pulmonary embolism (blood clot in lungs)
- Pulmonary edema (fluid in lungs)
- High altitude ascension could also lead to low partial pressure of oxygen in the arterial blood.
Hypoventilation: This refers to a condition wherein the oxygen (PaO2) content in the blood decreases and a marked increase in the levels of carbon dioxide is observed. This lowered PaO2 content can cause hypoxemia.
Low Inspired Oxygen: The FiO2 content in the blood is called the fraction of inspired oxygen in the blood. A decrease in this fraction of inspired oxygen may cause hypoxemia.
Right to Left Shunt: A right-to-left shunt refers to a condition in which there is a transfer of blood from the right side of the heart to its left side. An opening between the atria, ventricles, or blood vessels can lead to this. Structural defect or a problem in a heart valve can also result in right to left shunt.
Ventilation-Perfusion Mismatch: This is a condition in which an imbalance between the volume of gas expired by the alveoli (alveolar ventilation) and the pulmonary capillary blood flow is seen. This mismatch may cause hypoxemia.
Diffusion Impairment: In this condition, a marked reduction is seen in the oxygen movement from the alveoli to capillaries. This restricted movement may trigger hypoxemia.
More often than not, it is difficult to decide one single cause of hypoxemia in acute illnesses. It also becomes almost impossible to determine the extent of contribution of the causes of hypoxemia in such cases.
Now that you have some idea about the circumstances under which one may develop hypoxemia, let's move on to the treatment options for this pathological condition.
Mechanical Ventilation: Mechanical ventilation is a mechanism by which it is possible to aid or substitute spontaneous breathing mechanically. Continuous Positive Airway Pressure (CPAP) refers to a type of device that forces a steady stream of air into the nasal passage. This flow is set at a pressure that can overcome obstructions, thereby preventing the airway from closing. The pressure to be maintained should be determined through careful observation.
Supplemental Oxygen Therapy: In severe cases, it becomes essential to administer oxygen to the patient. Oxygen may be supplied through oxygen concentrators, cylinders or tanks. However, it is crucial to determine the precise levels of oxygen to be administered. Special care needs to be taken during supplemental oxygen therapy for infants. Supplemental oxygen therapy and CPAP are usually prescribed together as a treatment for hypoxemia. This is particularly effective for treating hypoxemia caused due to hypoventilation.
Transfusion of Packed RBCs: Packed red blood cells refers to the concentrate of red blood cells obtained after the removal of plasma in the blood. Packed red blood cells can be transfused as a treatment option for patients suffering from hypoxemia. This is known to increase the oxygen-carrying capacity of the blood. Sufficient care should be taken during the blood transfusion to avoid infections. This form of treatment cannot be used in case of patients who develop polycythemia (which is characterized by abnormally high RBC count) as a result of chronic hypoxemia.
Increasing Inspired Oxygen: This form of treatment is effective for hypoxemia that develops as a result of hypoventilation or due to the reduction in inspired oxygen.
Since hypoxemia can be caused by serious medical conditions, it is extremely essential to identify the underlying cause. Treating the underlying condition can certainly help to bring back the partial pressure of oxygen in arterial blood to normal. Drug therapy, oxygen therapy and lifestyle modification can certainly help in normalizing the partial pressure of oxygen in arterial blood.
Disclaimer: This HealthHearty article is for informative purposes only, and should not be used as a replacement for expert medical advice.