A new method for the measurement of percent oxyhemoglobin

A new method is presented for the spectrophotometric determination of percent oxyhemoglobin (percent saturation) in whole blood. The method is based on a theory of light absorption and scattering by particulate suspensions and requires the measurement of optical densities (D) of blood at three closely spaced wavelengths. The contribution of scattering to the optical density at each wavelength is determined from optical density values at two isosbestic wavelengths (546 and 520 nm) and the optical density at the third wavelength (555 nm) is related to the extent of oxygenation of the hemoglobin. The wavelength independence of the scattering contribution (B) induced by red cells was established from 510 and 575 nm. The optical density of red blood cell suspensions was measured with a spectrophotometer and a linear relationship was found between percent saturation and the corrected optical density ratio, (D555 B)/(D546 B). For a given saturation, this ratio was independent of optical path length (0.1-2 mm) and hematocrit (3-50%).