Design and evaluation of an instrument to measure microcirculatory blood flow and oxygen saturation simultaneously

There are compelling clinical advantages in being able to monitor, simultaneously and continuously, blood oxygen saturation and tissue perfusion from the same volume of tissue. We describe the design of a new instrument capable of combining both functions. It uses a laser diode at 805 nm to give a blood flow index and oxygenation information at that wavelength, and a pulsed LED at 660 nm to complete the estimation of oxygen saturation. By using a compensating photodetector these readings can be made relatively insensitive to sampling site. After calibrating the instrument on forehead sites it reliably read the oxygen saturation of sites on the thigh with a bias of -0.2% and a precision of +/- 1.7% relative to an IL 282 CO-oximeter.