You are a living repository of oxygen. Without oxygen, you are not alive. Without oxygen, you are different: you don’t have lungs or nose; you have rough, scaly skin; and you do not feel tired. If there’s no oxygen, you are not seating in front of your computer right now. You cannot browse the Internet nor create a facebook account. Say that you don’t need oxygen, and I would assume that you are an alien reading this.

Well, you are not an alien (hopefully). You need oxygen. You are breathing oxygen. Your body is a system of blood circulating with oxygen. Oxygen keeps you alive. But how would you know that you have enough oxygen in your blood?

Actually, there are two answers; one is the difficult, painful way, while the other is the comfortable, carefree way. The difficult and painful way is through the direct acquisition of blood sample. The nurse or the doctor will get a sample of your blood to test your oxygen saturation. Your nurse might use an injection or might prick your finger. Of course, the very thought of injection― even of blood seeping from your open wound― might scare the hell out of you. How much more if you have respiratory or cardiac problems? And in an emergency, say a car accident, will your nurse be able to find the time and convenience to puncture your finger and draw out blood from you?

That is why there is another option, the straight path, the calm river bend: the use of indirect, noninvasive means of knowing one’s blood oxygenation. No injection, prick or wound is needed. All that your nurse (or even you) has to do is attach a gadget somewhere on your body, and voila, you’ll know the measure of your blood oxygenation. One gadget that doctors and nurses all over the world use now is the pulse oximeter.

The pulse oximeter is a medical technology that acts as an oxygen monitor because it measures the percentage of hemoglobin (oxygen-transporting substance in blood) that is mixed with oxygen. It has a probe that is attached to a specific translucent body part (finger or ear lobe). The probe contains a pair of small light-emitting diodes (LEDS); one is red and the other is infrared. The absorption of these lights differs between oxyhemoglobin (blood plus oxygen) and its deoxygenated form (the blood with removed dissolved oxygen).Therefore, to get the ratio of oxyhemoglobin and deoxyhemoglobin, you can simply take a look at the ratio of the absorption of the red and the infrared light. The gadget is connected to a unit that displays the percentage of oxygenation together with a signal for each pulse beat.

This device is advantageous especially if the procedure is conducted in a place where the patient’s oxygenation is unstable, such as in the intensive care unit, and in an operating or emergency room. A doctor would not want to repetitively draw out blood from his patient, especially in a surgery. Portable pulse oximeters also serve as an oxygen monitor among mountain climbers and athletes whose oxygenation might go down at high altitudes or under strenuous exercise.

However, oximetry is not an absolute measure of respiratory and circulatory insufficiency. Certainly, there is always a possibility that the device might go wrong.