Oxygen Saturation

Oxygen is a vital need for every living entity. But how do you go about measuring how much oxygen is contained in your blood, or in the water you drink or in the air you breathe? The answer lies in the term 'oxygen saturation'. Relative measurement of oxygen content that is carried or dissolved in a given medium is termed as oxygen saturation. In a human body, oxygen saturation is a measure of oxygen that is dissolved in blood. Let me state with an example - One hemoglobin molecule contains four molecules of oxygen. So how much oxygen would 100 hemoglobin molecules contain? 100 x 4, right? Say, these 100 hemoglobin molecules are carrying 380 oxygen molecules. So the oxygen saturation of blood can be calculated as (380/400) x 100 which is 95%. Oxygen saturation is often referred to as SpO₂.

Oxygen Saturation Levels: Their Implications
A normal human body needs a constant oxygen supply for healthy functioning. Low oxygen saturation levels identified in blood can lead to serious and life-threatening medical conditions. Normal oxygen levels in body range between 95-100% at sea level. If the percentage goes below the oxygen saturation normal range or drops even less than 80%, it indicates that the blood contains very low level of oxygen. Some facts to remember on this:

• If the oxygen saturation falls below normal oxygen saturation levels (i.e. less than 92%), there is a strong probability of body succumbing to respiratory ailments such as hypoxemia. Hypoxemia is a respiratory ailment diagnosed by symptoms of body ache, fatigue, shortness of breath and confusion.
• As the blood oxygen levels are low, the oxygen is unable to penetrate the walls of red blood cells. In cases of low oxygen levels in the body, people are afflicted with weakening eyesight, memory loss, weakening heart muscles, tingling fingers, chronic cough and water retention at feet and ankles.
• Low oxygen saturation in blood is most possible in cases of already existing respiratory illnesses, retention of excess fluid in body, sleep apnea and inhaling extremely polluted air.
• Not to miss, if the blood oxygen saturation is below 88%, no insurance company will pay for your medication.

How is it Measured?
Oximeter, a small device is used to measure the oxygen saturation in blood. The precision and accuracy of the measurement is based on various factors like hemoglobin level, percentage of inhaled oxygen, atmospheric temperature, arterial blood flow to vascular tissue in body, venous return of blood and the oxygenation capacity of the person. With the above factors and recordings by oximeter, an oxygen saturation curve can be achieved. This curve plots the oxygen saturation against the partial pressure of oxygen giving the p50 value. This value indicates the point where the hemoglobin has a 50% oxygen saturation value. With the help of this value, one can assess the index of oxygen affinity in blood. For a healthy human, the clinically accepted oxygen saturation level is 95% although the saturation value may vary between 97% - 99%.

Pulse oximeters although used for measuring oxygen saturation, cannot be used in certain medical conditions like carbon monoxide poisoning and cardiac arrest situations. This is because they fail to detect any difference between the oxygen and carbon monoxide bound to hemoglobin in blood.

How to Test Oxygen Saturation?
Testing for oxygen saturation can be done by two methods. One of them is by fitting a finger clip on your finger. The clip shines a light through a side of the finger and the light is measured from the other end by a detector. Blood cells with different levels of oxygen saturation exhibit a different color. Blood cells give a bright red color if they are loaded with oxygen. Else the color is a bluish tinge indicating that there is not enough oxygen in the blood cell. The finger clip gives a rough estimate of oxygen saturation value which is not precise. The better alternative is to go for an arterial blood gas test. Usually, for blood tests, blood is drawn from veins. In this test, however, blood is drawn from arteries (the artery for blood test is mostly in the wrist). This test provides with the exact value of the oxygen saturation. Both these procedures yield fast results with the former being available immediately and the later being available in a span of 15 minutes.

Hope the above information was helpful in understanding oxygen saturation, how it is measured and how it needs to be tested. So if a low oxygen saturation level is observed in your blood (less than 90%), seek immediate medical attention!