Oxygen saturation: normal and pathological values in the elderly and children

By Cristiano Antonino On Apr 21, 2023

Oxygen saturation (more correctly ‘arterial haemoglobin saturation’) in medicine refers to the saturation of haemoglobin in arterial blood

Physiology

The tissues of the human body constantly need an adequate amount of oxygen to survive.

Red blood cells transport the oxygen the body needs from the lungs to the body via the arteries.

The saturation level is nothing more than an index representing the percentage of haemoglobin saturated with oxygen, in relation to the total amount of haemoglobin in the blood.

A reduced load of oxygen carried by the erythrocytes (saturation) may be due to certain diseases: too low a saturation could be a sign of respiratory or circulatory problems.

Oxygen saturation, how is it measured?

Saturation is normally measured by a doctor or nurse with a pulse oximeter or oximeter or saturation meter, a portable instrument that is placed on a finger or ear painlessly.

Portable saturimeters, whether adult or paediatric, i.e. for children, all work on the same principle: they measure the haemoglobin present in the blood, and from this they estimate the amount of oxygen present in the blood.

In addition to this (main) function, saturation meters are usually also equipped with a heart rate detector.

And by the way, taking a measurement with a saturation meter is very simple.

Simply place the instrument’s sensors

at the fingertip of a finger of the hand or foot;
at the earlobe.

The display of the device then returns the values automatically.

What to do if the saturimeter does not work?

If the instrument fails to detect data, it may be useful to try changing the position on the finger or changing the finger altogether.

Detection may not occur correctly or not at all:

if the saturimeter is malfunctioning or has a flat battery;
if the saturimeter is removed too quickly from the finger;
if the finger is cold (in this case it is useful to warm the finger by rubbing it with the other hand or by lowering the hand towards the ground so that the force of gravity causes blood to pool on the finger);
if there is a glove on the hand;
if there is nail varnish and/or false nails on the finger.

Oxygen saturation, normal values

A physiological measurement of saturation ‘in room air’, i.e. without artificial ventilation, reported as ‘SpO²’, is between 95% and 99%, usually around 97%, in both adults and children.

Slightly different values do not necessarily indicate pathology: e.g. in the elderly, the value may be normal despite being slightly lower than physiological values, e.g. around 93%.

Sometimes even values around 90%, thus apparently pathological, may in reality be normal in some patients: this is the case with people suffering from chronic obstructive pulmonary disease (COPD).

Values between 99% and 100% may be normal in the case of artificial oxygen administration, e.g. in oxygen therapy.

Oxygen saturation, low values and hypoxia

SpO² values between 90 and 95% indicate a partial absence of oxygen (mild hypoxia, potentially indicative of pathology), while values below 90% are not physiological and indicate severe oxygen deficiency (severe hypoxia) requiring oxygen therapy and urgent ventilatory assistance for children and adults.

High values and hyperventilation

A value of 100 measured ‘in room air’ may be a symptom of hyperventilation, which may be due, for example, to panic attacks.

Impaired oxygen saturation: is it serious?

A saturation below 90 is potentially serious and is generally an indication of respiratory or haematological pathology causing hypoxia.

The severity of an impaired saturation depends on many factors:

its duration (the condition may be acute or chronic);
the possible presence of other pathologies or conditions (e.g. blood vessel wall disease, coagulation disease, tumours, diabetes, high blood pressure, trauma, malnutrition, malabsorption, pregnancy);
the patient’s age.

Each case of altered arterial haemoglobin saturation is highly subjective and its severity should not be overestimated, but neither should it be underestimated.

When the alteration is mild, perhaps even transient, not recurrent and in the absence of other symptoms such as dyspnoea, dizziness, general malaise, it is generally not a cause for concern and often no treatment is even necessary.

An elevated alteration in saturation that lasts over time and leads to symptoms undoubtedly requires further rapid medical investigations, in addition to artificial oxygen administration, because it could be caused by even serious pathologies that require prompt treatment.

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