Pulse oximetry has revolutionized the ability to monitor oxygenation in a continuous, accurate, and non-invasive fashion. Despite its ubiquitous use, it is our impression and supported by studies that many providers do not know the basic principles behind its mechanism of function. This knowledge is important because it provides the conceptual basis of appreciating its limitations and recognizing when pulse oximeter readings may be erroneous. In this review, we discuss how pulse oximeters are able to distinguish oxygenated hemoglobin from deoxygenated hemoglobin and how they are able to recognize oxygen saturation only from the arterial compartment of blood. Based on these principles, we discuss the various conditions that can cause spurious readings and the mechanisms underlying them.

The pulse oximeter allows pilots to monitor the oxygen saturation of hemoglobin in their blood, an invaluable tool when climbing above 10,000 feet.

The use of a pulse oximeter allows pilots to monitor the oxygen saturation of hemoglobin in their blood. How a pulse oximeter works is pretty ingenious. Rather than directly measuring hemoglobin concentration, the small device, which costs about $40 and can be purchased online, takes constant measurements of the absorption of specific wavelengths of light in oxygenated hemoglobin. Blood is red due to the quality of oxyhemoglobin it contains, causing it to absorb light of certain wavelengths. The pulse oximeter incorporates two LEDs, one red and one infrared. Infrared light is absorbed by the oxyhemoglobin and red light by the reduced hemoglobin. The oxygen saturation of the blood determines the degree of light absorption, and the result is shown on a digital display of oxygen saturation on the pulse oximeter’s screen.

On the ground, your oxygen saturation level should be around 98 percent. As you climb, your goal is to keep your blood-oxygen level above 90 percent. When using a mask, you should find it easy to keep your blood-oxygen level at 95 percent or higher. If you’re using a cannula and talking a lot or exerting yourself, make sure you take the time to relax and breath through your nose