Oxygen Saturation: Measuring the Oxygen Levels in Blood, Air or Water

I have mentioned many times in my articles the fact that the blood oxygen monitor or the pulse oximeter is a medical device which measures the blood oxygen saturation. However, what exactly is oxygen saturation? Is it a purely medical notion? Can it be applied to other areas of research as well?

The term ‘oxygen saturation’ (or ‘dissolved oxygen’) indicates the amount of oxygen present in a certain medium. The term is being used in several fields: medicine, environmental research, vehicle construction etc.

In the medical field, ‘oxygen saturation’ indicates the blood oxygen levels of a patient or – in one word – his or her oxygenation. But how does our blood get oxygenated? As we all know, oxygen or O₂ enters our body through the lungs during the breathing process. The lungs have the capacity of transporting the atmosphere oxygen into our bloodstream. After being oxygenated, the blood changes its color from dark purple to red – as we all know it. The oxygen saturation, therefore, indicates the percentage of hemoglobin saturated with oxygen.

The blood oxygen saturation can be influenced by many factors: certain medical conditions (such as pulmonary or cardio-vascular diseases), altitude or physical effort. At sea level, the normal oxygen saturation of a healthy person is > 95%. If the oxygen levels in the blood are lower than 90%, it may lead to dangerous complications. There is a really thin line between normal oxygenation (95-98%) and respiratory failure (85-90%). An oxygen saturation of 100% is not normal when breathing simple air; it can be achieved only during supplemental oxygen therapy for shorts periods of time: an excess of oxygen, just like its deficiency, could be life-threatening.

As I mentioned in my previous posts, there are two main ways of measuring the oxygen saturation levels of a person: traditional blood tests and pulse oximetry.

Pulse oxymeters or blood oxygen monitors come in different types and sizes – from the compact finger oxygen monitor for personal use to the complex medical tabletop monitors used in hospitals. The oxygen saturation values delivered by pulse oximetry are also referred to as SpO₂.

These monitors can be used for various purposes, depending on the needs of the patient. Some people (especially athletes, mountaineers and pilots) may need to check on their oxygenation from time to time to determine their body’s response to extreme conditions. The same procedure is advisable for people who suffer from a certain chronic disease.

Patients in a critical condition or infants suffering from sleep apnea, however, may need a continuous measurement. In such cases, the use of an oxygen monitor with alarm is recommended. Whenever the oxygen saturation will drop below a limit programmed in advance (for example, 90%), the alarm will sound.

Environmental oxygen saturation usually indicates how much oxygen is dissolved in the ambient air, in the soil or in water. These measurements can alert researchers if an ecosystem’s sustainability is being threatened. For example, if there is insufficient oxygen in a certain environment (a lake or a river) it may lead to the gradual extinction of aerobic organism, at the same time contributing to the development of dangerous anaerobic organisms. Dissolved oxygen monitors are usually used by specialists to measure the oxygen saturation in a given liquid medium. Ideally, in fresh water the Dissolved Oxygen Concentration should be at least 4 milligrams per liter (ppm). Salty waters (seawater) have a lower oxygen saturation.

The oxygen saturation in the breathing air is determined by using oxygen deficiency monitors – these devices are especially helpful in factories and other industrial facilities prone to gas leakages. The normal oxygen levels in the ambient air range around 21%.