What is oxygen saturation?
Oxygen saturation indicates what proportion of the red blood pigment (hemoglobin) is loaded with oxygen. The hemoglobin absorbs the oxygen inhaled via the lungs and transports it to the tissues via the bloodstream. There, the hemoglobin releases the charged oxygen molecules to the cells. A distinction is made between:
- sO2: oxygen saturation without more precise designation
- SaO2: oxygen saturation in arterial blood
- SVO2: oxygen saturation in venous blood
- SZVO2: Oxygen saturation in central venous blood
The pressure exerted by gaseous oxygen in the blood is called the partial pressure of oxygen.
What factors affect oxygen saturation?
Oxygen saturation in blood depends on its pH, carbon dioxide partial pressure, temperature, and the concentration of bisphosphoglycerate in red blood cells. Hemoglobin releases oxygen more readily at:
- increased CO2 concentration
- increased temperature
- increased concentration of 2,3-bisphosphoglycerate in red blood cells
On the other hand, opposite conditions (increased pH, decreased CO2 concentration, etc.) stabilize the binding of oxygen to hemoglobin.
When do you determine oxygen saturation?
The physician measures the oxygen saturation in the arterial blood (SaO2) with a so-called pulse oximeter – a small portable measuring device. A measuring clip is attached to the patient’s fingertip or earlobe and transmits the measured values to a monitor. Heart rate, respiratory rate and blood pressure are usually measured simultaneously. For newborns, the clip can also be attached to the heel.
Oxygen saturation: Normal values
Neither age nor gender influence oxygen saturation. Values in healthy people should be between 90 and 99 percent.
The partial pressure of oxygen in the blood, on the other hand, depends on age and is measured either in kPa or mmHg. Young adults usually show a spO2 value of about 96 mmHg (equivalent to 12.8 kPa). Over the course of life, the partial pressure decreases and is about 75 mmHg (equivalent to 10 kPa) in an 80-year-old.
If there is too little oxygen in the blood due to a lung disease, less hemoglobin can be loaded with oxygen – oxygen saturation drops. This is the case, for example, with:
- emphysema
- Asthma
- Chronic obstructive pulmonary disease (COPD)
Decreased respiration also decreases saturation, for example, in the case of intoxication with mind-obscuring substances. Other reasons for decreased oxygen saturation include:
- Circulatory disorders
- Heart defects
- Disorders of the acid-base balance with acidosis (hyperacidity)
False low values can be caused by hypothermia or restricted blood flow to the extremities (such as in shock or vascular occlusion). Nail polish and nail fungus can also falsify the reading.
When is oxygen saturation elevated?
If you breathe in and out particularly deeply and rapidly (hyperventilation), the saturation can rise up to 100 percent. At the same time, the carbon dioxide content in the blood decreases.
What to do if oxygen saturation changes?
If the oxygen saturation is too low, oxygen therapy is necessary. In this case, oxygen is supplied to the patient, for example, via a nasal cannula or a mask. If necessary, the patient may also need to be intubated: A tube is inserted into the trachea, and the patient is artificially ventilated.
In addition, the cause of the lowered oxygen saturation must be remedied. For example, an asthma attack is stopped with medication.
