Clinical applications and issues of oxygen saturation level measurements obtained from peripheral sites

Studies have suggested that the saturated oxygen level within one's arterial blood can provide crucial information about the status of one's cardiopulmonary system. Currently, a popular and convenient approach is to obtain this vital physiological sign through non-invasive measurement on suitable peripheral sites such as a finger, toe or ear lobe. This measurement is known as the SpO2 parameter. It has been increasingly adopted in not only clinical settings but also remote monitoring purposes. In order to measure this optical based parameter, light sources of both the red and infrared wavelengths are required. The most recognized waveform feature is the peripheral pulse or its AC component which is synchronized to each heartbeat. The AC component is superimposed on a constant DC baseline attributed to breathing efforts, sympathetic nervous system activities and thermoregulation. The popularity of the SpO2 parameter may be due to its viable cost, simplicity to build and portability. Moreover, the basic building blocks of a SpO2 based measurement consists of control, filtering and amplification functions that can easily be incorporated with an embedded system. In this review, a brief description of the SpO2 measurement, its normative values and technical issues in its application as a clinical monitor are discussed.