Which of these two parameters does a pulse oximeter measure? 1. O2Hb 2. Hb 3. COHb 4. MetHb

a. 1 and 2
b. 1 and 3
c. 2 and 3
d. 3 and 4

ANS: A
Pulse oximetry provides continuous, noninvasive measurements of arterial oxygen saturation. A sensor is placed over a digit, an earlobe, the forehead or the bridge of the nose; this sensor measures the absorption of selected wavelengths of light beamed through the tissue (Fig. 10-1). For example, oxyhemoglobin can be differentiated from deoxygenated hemoglobin by shining two wavelengths of light (660 and 940 nm) through the sampling site. As Figure 10-2 illustrates, at a wavelength of 660 nm (red light), deoxygenated hemoglobin absorbs more light than oxy-hemoglobin. Conversely, oxyhemoglobin absorbs more light at 940 nm (infrared light [IR]) than does deoxygenated hemoglobin.