Oxygen saturation rate o2 : definition, measurement and standards
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The measurement of oxygen saturation is an examination that allows the evaluation of the hematosis function: the oxygenation of the blood. This analysis of oxygen saturation is particularly used in people with a respiratory pathology.
Definition of oxygen saturation level
Blood supplies oxygen to all tissues and transports carbon dioxide to the lungs for removal from the body. A small amount of oxygen is carried by plasma. Most of it is carried by hemoglobin in the red blood cells.
Blood oxygen is expressed in three ways:
the percentage saturation of its main carrier hemoglobin (SaO2),
the pressure exerted in the blood in a dissolved manner (PaO2)
its quantity in the blood (CaO2).
In case of respiratory dysfunction, the blood contains less oxygen and more carbon dioxide. The degree of oxygenation can be measured with two means: oxygen saturation (SaO2, measured in arterial blood, SpO2 measured by a pulse oximeter or saturometer) and oxygen partial pressure (PaO2).
Oxygen saturation (SaO2) is the percentage of oxygen-saturated hemoglobin (oxyhemoglobin) relative to the total amount of hemoglobin in the blood. Oxygen saturation is measured to assess the function of hematosis: the oxygenation of the blood.
The different measurements
The oxygen saturation level can be measured in two ways:
By arterial blood sampling (blood gas measurements).
This involves taking a blood sample from an artery. This is the only technique that allows a reliable and definitive measurement of blood gases. Arterial blood gas analysis allows the analysis of the acid-base balance (pH) and the measurement of the arterial oxygen pressure (PaO2) and carbon dioxide pressure (PaCO2), which provides information on the respiratory status. Oxygen saturation of hemoglobin measured by arterial blood sampling is expressed as Sao2. Oxygen saturation is measured directly in the red blood cells.
With a pulse oximeter or saturometer (easiest to use)
A pulse oximeter or saturometer is a device that non-invasively measures the oxygen saturation of the blood. This device is most commonly used in hospitals to monitor patients who are in respiratory distress or who are on invasive or non-invasive ventilatory support (oxygen therapy). It is equipped with a light emitter and receiver that allows the determination of blood oxygen saturation.
It transmits a light beam through the tissue, most often a finger or toe in adults, but also the nose or earlobe, or the hand or foot in young children. Oxygen saturation of hemoglobin measured by pulse oximetry is expressed as SpO2 (the p standing for pulse saturation). This is called pulsed hemoglobin oxygen saturation.
Indications for measuring oxygen saturation
There are several indications for measuring the oxygen saturation level by saturometer in adults:
During anesthesia or in the monitoring room after surgery
In emergency medicine departments
In intensive care units, especially for people who are or may be ventilated.
In children, oxygen saturation measurement also has several indications:
evaluation of the severity of a respiratory pathology (bronchiolitis, pneumonia, asthma...)
assessment of the severity of bronchiolitis in infants; a saturation below 94% is one of the indicators of severity
evaluation of the effectiveness of an aerosol
detection of possible cardiopathy in a cyanotic newborn
Arterial blood gas is performed when the respiratory status is severe and when a major metabolic disorder is suspected.
Oxygen saturation standards
Normal oxygen saturation for a healthy person is between 95% and 100% depending on age. SpO2 (Pulse saturation measured with a pulse oximeter). It is insufficient below 95%. It is called hypoxemia. The notion of hypoxemia applies to any insufficiency of oxygenation of the blood and thus as soon as the SpO2 is lower than 95%. The 90% limit marks a hypoxemia corresponding to the equivalent of respiratory failure.
Normal arterial oxygen saturation (SaO2) is between 96% and 98% in a young adult and 95% in a person over 70 years old. When it is lower than 90%, the person is said to be desaturated. Desaturation also corresponds to a drop of 4 points in saturation compared to the baseline value (for example during an effort).
A "normal" SpO2 for a child corresponds to a value above 95%. An SpO2 level below 94% in a child is a criterion of severity and leads to hospitalization. SpO2 measurement is very important in children, because a child only appears cyanotic (bluish in color) when SaO2 is less than 75% and because arterial blood gas measurements are very rarely performed in children. The pulse oximeter is essential to detect early hypoxia.
Low saturation levels
Hypoxemia occurs when the oxygen saturation value is below 93%. The main risk is that of cellular suffering (ischemia) resulting from insufficient oxygen supply to the various tissues of the body. Acute hypoxemia can occur following an acute exacerbation of asthma, acute heart failure, pneumonia or an acute exacerbation of Chronic Obstructive Pulmonary Disease (COPD), following a pulmonary embolism, pleural effusion, pneumothorax.
Symptoms of low oxygen saturation
Hypoxemia (oxygen saturation level below 93%) is manifested by shortness of breath, accelerated and shallow breathing, bluish skin (cyanosis) but all these signs are less specific and sensitive than pulse oximetry.
Low oxygen saturation and COVID-19
COVID-19 can cause low oxygen saturation. The most severe cases of COVID can lead to pneumonia resulting in acute respiratory distress syndrome. Symptoms are fairly mild at first. That's why doctors may monitor oxygen saturation levels with an oximeter. Difficulty breathing and shortness of breath are signs that you should call emergency services.
Caution: Using a pulse oximeter is also prone to error and it is best to learn how to use it with a healthcare professional.
Saturation level too high
Too much oxygen during oxygen therapy can lead to hyperoxia. Hyperoxia is dangerous for people with respiratory failure.
Treatments for hypoxemia
If hypoxemia (oxygen saturation below 93) occurs, oxygen therapy can be initiated. Oxygen can be administered nasally (goggles) or nasally and orally (masks) but also by artificial ventilation (ventilator, intubation) or by extracorporeal circulation (ECMO). The amount of oxygen administered is guided by arterial blood gases or pulse oximetry to maintain Pao2 between 60 and 80 mmHg (saturation of 92 to 100%) without causing oxygen toxicity.
Definition of oxygen saturation level
Blood supplies oxygen to all tissues and transports carbon dioxide to the lungs for removal from the body. A small amount of oxygen is carried by plasma. Most of it is carried by hemoglobin in the red blood cells.
Blood oxygen is expressed in three ways:
the percentage saturation of its main carrier hemoglobin (SaO2),
the pressure exerted in the blood in a dissolved manner (PaO2)
its quantity in the blood (CaO2).
In case of respiratory dysfunction, the blood contains less oxygen and more carbon dioxide. The degree of oxygenation can be measured with two means: oxygen saturation (SaO2, measured in arterial blood, SpO2 measured by a pulse oximeter or saturometer) and oxygen partial pressure (PaO2).
Oxygen saturation (SaO2) is the percentage of oxygen-saturated hemoglobin (oxyhemoglobin) relative to the total amount of hemoglobin in the blood. Oxygen saturation is measured to assess the function of hematosis: the oxygenation of the blood.
The different measurements
The oxygen saturation level can be measured in two ways:
By arterial blood sampling (blood gas measurements).
This involves taking a blood sample from an artery. This is the only technique that allows a reliable and definitive measurement of blood gases. Arterial blood gas analysis allows the analysis of the acid-base balance (pH) and the measurement of the arterial oxygen pressure (PaO2) and carbon dioxide pressure (PaCO2), which provides information on the respiratory status. Oxygen saturation of hemoglobin measured by arterial blood sampling is expressed as Sao2. Oxygen saturation is measured directly in the red blood cells.
With a pulse oximeter or saturometer (easiest to use)
A pulse oximeter or saturometer is a device that non-invasively measures the oxygen saturation of the blood. This device is most commonly used in hospitals to monitor patients who are in respiratory distress or who are on invasive or non-invasive ventilatory support (oxygen therapy). It is equipped with a light emitter and receiver that allows the determination of blood oxygen saturation.
It transmits a light beam through the tissue, most often a finger or toe in adults, but also the nose or earlobe, or the hand or foot in young children. Oxygen saturation of hemoglobin measured by pulse oximetry is expressed as SpO2 (the p standing for pulse saturation). This is called pulsed hemoglobin oxygen saturation.
Indications for measuring oxygen saturation
There are several indications for measuring the oxygen saturation level by saturometer in adults:
During anesthesia or in the monitoring room after surgery
In emergency medicine departments
In intensive care units, especially for people who are or may be ventilated.
In children, oxygen saturation measurement also has several indications:
evaluation of the severity of a respiratory pathology (bronchiolitis, pneumonia, asthma...)
assessment of the severity of bronchiolitis in infants; a saturation below 94% is one of the indicators of severity
evaluation of the effectiveness of an aerosol
detection of possible cardiopathy in a cyanotic newborn
Arterial blood gas is performed when the respiratory status is severe and when a major metabolic disorder is suspected.
Oxygen saturation standards
Normal oxygen saturation for a healthy person is between 95% and 100% depending on age. SpO2 (Pulse saturation measured with a pulse oximeter). It is insufficient below 95%. It is called hypoxemia. The notion of hypoxemia applies to any insufficiency of oxygenation of the blood and thus as soon as the SpO2 is lower than 95%. The 90% limit marks a hypoxemia corresponding to the equivalent of respiratory failure.
Normal arterial oxygen saturation (SaO2) is between 96% and 98% in a young adult and 95% in a person over 70 years old. When it is lower than 90%, the person is said to be desaturated. Desaturation also corresponds to a drop of 4 points in saturation compared to the baseline value (for example during an effort).
A "normal" SpO2 for a child corresponds to a value above 95%. An SpO2 level below 94% in a child is a criterion of severity and leads to hospitalization. SpO2 measurement is very important in children, because a child only appears cyanotic (bluish in color) when SaO2 is less than 75% and because arterial blood gas measurements are very rarely performed in children. The pulse oximeter is essential to detect early hypoxia.
Low saturation levels
Hypoxemia occurs when the oxygen saturation value is below 93%. The main risk is that of cellular suffering (ischemia) resulting from insufficient oxygen supply to the various tissues of the body. Acute hypoxemia can occur following an acute exacerbation of asthma, acute heart failure, pneumonia or an acute exacerbation of Chronic Obstructive Pulmonary Disease (COPD), following a pulmonary embolism, pleural effusion, pneumothorax.
Symptoms of low oxygen saturation
Hypoxemia (oxygen saturation level below 93%) is manifested by shortness of breath, accelerated and shallow breathing, bluish skin (cyanosis) but all these signs are less specific and sensitive than pulse oximetry.
Low oxygen saturation and COVID-19
COVID-19 can cause low oxygen saturation. The most severe cases of COVID can lead to pneumonia resulting in acute respiratory distress syndrome. Symptoms are fairly mild at first. That's why doctors may monitor oxygen saturation levels with an oximeter. Difficulty breathing and shortness of breath are signs that you should call emergency services.
Caution: Using a pulse oximeter is also prone to error and it is best to learn how to use it with a healthcare professional.
Saturation level too high
Too much oxygen during oxygen therapy can lead to hyperoxia. Hyperoxia is dangerous for people with respiratory failure.
Treatments for hypoxemia
If hypoxemia (oxygen saturation below 93) occurs, oxygen therapy can be initiated. Oxygen can be administered nasally (goggles) or nasally and orally (masks) but also by artificial ventilation (ventilator, intubation) or by extracorporeal circulation (ECMO). The amount of oxygen administered is guided by arterial blood gases or pulse oximetry to maintain Pao2 between 60 and 80 mmHg (saturation of 92 to 100%) without causing oxygen toxicity.