blood analysis

Oxygen saturation

Generality

Oxygen saturation is a blood index that reflects the percentage of hemoglobin saturated with oxygen compared to the total amount of hemoglobin present in the blood.

Under normal conditions, during the passage in the lungs, the red blood cells rich in hemoglobin are charged or saturated with oxygen, which will then be transported and transferred to the various tissues of the body.

What's this

Oxygen saturation is a parameter that reflects the percentage of oxygen molecules linked to hemoglobin (oxyhemoglobin), thus making it possible to establish the state of hypoxemia (reduced amount of O 2 available in the blood).

The oxygen saturation is measured with a transcutaneous electromedical instrument, called the oximeter (oximeter or pulse oximeter), with a shape similar to that of a clothespin.

This device is equipped with a probe and two photo-emitting diodes (sensors that emit light rays of different wavelengths between them and communicate with a photocell). The blood index is then estimated by absorbing the light emitted by the oximeter applied to a finger of the hand or an ear lobe (anatomical regions rich in capillaries).

The useful element for the evaluation of oxygen saturation is the color of the blood, which, when oxygenated, is a bright red tint, vice versa, it is darker.

Why do you measure

Non-invasive monitoring of oxygen saturation values ​​is important both at home and during health emergencies, to quickly assess the need for assisted ventilation.

Monitoring of oxygen saturation values ​​is not important for diagnostic purposes only, but it is also essential to evaluate the efficacy of drug therapies or other treatments undertaken to restore oxygen saturation to normal values, or to cure the underlying disease ( eg bronchodilators).

Normal values

Oxygen saturation is considered normal when the values ​​are higher than 95%, while it starts to become pathological if equal or less than 90%.

If the oximeter shows indices lower than 95%, we speak of hypoxia, which can be mild (between 91-94%), moderate (between 86-90%) and severe (equal to or less than 85%).

High Oxygen Saturation

High levels of oxygen saturation are not usually associated with medical problems and / or pathological consequences, therefore they are not considered clinically relevant.

Low Oxygen Saturation

Hypoxemia, characterized by low oxygen saturation values, is typical of various diseases:

  • Airway obstructions;
  • Anemia;
  • Acute respiratory distress syndrome;
  • COPD;
  • Emphysema;
  • Interstitial lung disease;
  • Pneumonia, pneumothorax;
  • Pulmonary edema;
  • Pulmonary embolism;
  • Pulmonary fibrosis;
  • Obstructive sleep apnea syndrome.

Even altitude and anemia are associated with hypoxic pictures, for example between 5, 000 and 5, 500 m of altitude, oxygen saturation drops to around 85%.

Hypoxia is also observed in patients with atherosclerosis, angina, heart attack, stroke, head injury and rib fractures. Furthermore, a lack of oxygen can occur in case of drug intoxication, carbon monoxide or heavy metals (such as mercury).

How to measure it

Oxygen saturation can be determined on an arterial blood sample, usually taken from the radial artery of the wrist.

The examination is not painful, although some patients consider it a little more annoying than the classic venous withdrawals from a vein in the forearm.

Oxygen saturation can also be measured non-invasively through portable devices called pulse oximeters (or oximeters or oximeters), which allow you to quickly estimate the amount of hemoglobin bound to oxygen by applying the appropriate sensor to a finger of the hand or to the lobe of an ear.

Preparation

The measurement of oxygen saturation is performed in an outpatient manner and does not require special preparation.

Removal of the nail polish before the examination is important, in order not to alter the results.

The amplitude of the pulse oximeter signal can be conditioned by arrhythmias, hypotension or profound systemic vasoconstriction.

Interpretation of Results

The oximetry allows to know if the blood oxygenation values ​​are normal or lower than the norm. The results make it possible to identify whether there is respiratory failure and of what extent, to set up an eventual oxygen therapy.

A reduced amount of oxygen in the blood can lead to hypoxemia. This condition involves manifestations such as pallor of the skin and mucous membranes (cyanosis), hyperventilation and dyspnea, as well as generating a state of confusion and disorientation. Often, hypoxemia is associated with hypoxia, ie a lack of oxygen available in the tissues.

The causes are attributable to ventilation and oxygenation disorders, such as sleep apnea, pneumonia, pulmonary embolism and respiratory failure. In fact, these pathological conditions involve alveolar hypoventilation, ie the air leaving the lungs is less rich in oxygen than the norm. This can also happen when the upper respiratory tract is occluded, thus preventing the passage of oxygen. Clearly, this deficit causes damage correlated to the duration of the hypoxic event itself: from the diminished synthesis of ATP, to cell death.

Normal and Pathological Values

The percentage of oxygen-saturated hemoglobin in normal conditions is greater than 95%, with optimal values ​​around 97-98%.

However, in the presence of some diseases, mainly pulmonary, a lower percentage of red blood cells binds and transports oxygen to the body; consequently, oxygen saturation falls below 95% and, once it reaches values ​​below 90%, we speak of hypoxemia, or a reduced amount of oxygen in the blood.

A value less than 80% shows a serious hypoxic state.