- 1. Pulse oximeter (or finger)
- 2. Arterial blood gas analysis
- Normal values of oximetry
- Care for a more accurate result
Oximetry is an exam capable of measuring blood oxygen saturation, that is, the percentage of oxygen being transported in the bloodstream. This measure is usually necessary when diseases that impair or interfere with the functioning of the lungs are suspected, such as asthma, emphysema, pneumonia, lung cancer, pulmonary congestion or neurological diseases, for example.
Generally, oximetry above 90% indicates good blood oxygenation, however, it is necessary for the doctor to evaluate each case. A low blood oxygenation rate may indicate the need for treatments such as a catheter or oxygen masks, and may indicate a life-threatening condition if proper treatment is not done. Understand the consequences of lack of oxygen in the blood.
There are two ways to take this exam:
1. Pulse oximeter (or finger)
It is the most used way to measure the amount of oxygen in the blood, where small devices are used, called pulse oximeters, which can do this measurement when placed on a finger or on the lobe of the ear.
The main advantage of this measure is the fact that it is not invasive, as there is no need to sting or collect blood. In addition to oximetry, this device may also be able to measure other vital data, such as the amount of heartbeat and respiratory rate, for example.
- How it works: The pulse oximeter has a light sensor that captures the amount of oxygen that passes in the blood under the place where the test is being done and, in a few seconds, indicates the value. These sensors take immediate, regular measurements and are designed for use on the fingers, toes or ears.
Pulse oximetry is widely used by doctors and other health professionals during clinical evaluation, especially in cases of diseases that cause difficulty in breathing, such as lung, heart and neurological diseases, or during anesthesia.
The oximeter can be purchased at medical or hospital supply stores, and is available in different brands and prices. It is recommended to obtain reliable brands, to avoid measurement errors.
2. Arterial blood gas analysis
Unlike pulse oximetry, arterial blood gas analysis is an invasive way of measuring the rate of oxygen in the blood, as it is done by collecting blood into a syringe, and for this a needle stick is needed to access the blood vessel that carries arterial blood. For this reason, this type of examination is less frequent than pulse oximetry.
The advantage of arterial blood gases is a more accurate measure of oxygen saturation levels in the blood, in addition to being able to provide other important measures, such as the amount of carbon dioxide, pH or amount of acids and bicarbonate in the blood, for example.
- How it works: it is necessary to perform an arterial blood collection and then this sample is taken to be measured in a specific device in the laboratory. The blood vessels most used for this type of measurement are the radial artery, in the wrist, or femoral, in the groin, but others can also be used.
This type of measurement is usually used only in cases where the patient needs to be monitored continuously or more accurately, which is more common in situations such as major surgery, severe heart disease, arrhythmias, generalized infection, sudden changes in pressure blood pressure or in cases of respiratory failure, for example. Learn what respiratory failure is and how it can decrease blood oxygenation.
Normal values of oximetry
A healthy person, with adequate oxygenation of the body, usually has an oxygen saturation above 95%, however, it is not uncommon that due to mild conditions, such as colds or flu, the saturation is not between 90 and 95%, without cause for concern.
When saturation reaches values below 90%, it may indicate that blood oxygenation is deficient, which can arise in more serious diseases such as asthma, pneumonia, emphysema, heart failure or neurological diseases, for example.
In arterial blood gases, in addition to the measurement of oxygen saturation, partial oxygen pressure (Po2) is also assessed, which must be between 80 and 100 mmHg.
In any case, the evaluation of the doctor or a health professional is always necessary, as other clinical data need to be evaluated in order to reach a conclusion about the cause and how the treatment should be done.
Care for a more accurate result
It is very important that the devices that make this type of measurement are calibrated regularly, to avoid altered results. In addition, when using the pulse oximeter, some precautions to avoid altering the exam include:
- Avoid using enamel or false nails, as they alter the passage of the light sensor; Keep the hand relaxed and below the level of the heart; Protect the device in a very bright or sunny environment; Observe if the device is well positioned;
Before taking the exam, the doctor should also investigate diseases such as anemia or impaired blood circulation, which can interfere with the measurement of blood oxygenation.
