Oxygen is essential for life. In order for humans to function properly, oxygen must be present in adequate amounts throughout the body. A person's oxygen saturation level measures the amount of oxygen carried in the blood. A number that falls too low can signal catastrophic consequences. That's why hospitals monitor oxygen saturation alongside pulse rate and blood pressure when determining a patient's condition.
Blood transports oxygen throughout the body thanks to haemoglobin, an iron-containing protein in red blood cells. Haemoglobin molecules can carry up to four oxygen molecules. The percentage of oxygen carried in the blood provides the saturation level.
For instance, if one haemoglobin molecule is carrying three oxygen molecules, the haemoglobin is carrying only 75 per cent of its total capacity. In a larger blood sample, 1,000 haemoglobin molecules could carry up to 4,000 oxygen molecules. If only 3,920 oxygen molecules are transported, that equals 98 per cent of total capacity. That means the blood's oxygen saturation level is 98 per cent.
If a person's oxygen saturation level is too low, it means inadequate amounts of oxygen are reaching vital organs and body cells. This can lead to respiratory failure and possiblly death.
While ideal levels may vary depending upon the individual, the oxygen saturation level for a young, healthy adult tends to fall between 95 and 100 per cent. Respiratory failure actually can set in when the oxygen saturation level drops to 90 per cent. That doesn't leave much deviation between normal and possibly fatal, so it's critical for doctors and nurses to monitor a patient's oxygen saturation at all times.
An accurate, easy way to measure oxygen saturation levels is through pulse oximetry. A pulse oximeter is a small clip that attaches to a patient's finger. The oximeter shines two bright lights, one red and one infrared, through the finger to measure the blood oxygen levels. It does this by analysing the colour of the arterial blood. Oxygen-rich blood is bright red. In order to tell the arterial blood apart from the surrounding tissue, the oximeter measures the change in the overall colour in coordination with the beating pulse.
Pulse oximeters require a strong regular pulse to register an accurate oxygen saturation reading. People with cold hands and feet can sometimes have weak pulses in their extremities, leading to inaccurate readings.
Despite some erroneous reports, the accuracy of pulse oximeters isn't affected when patients have anaemia, sickle cell disease or bilirubin in the blood.