Pulse Spectrophotometric Determination of Plasma Bilirubin in Newborns

In neonatal jaundice, plasma bilirubin has to be measured repeatedly in order to direct phototherapy. Invasive determination is standard. The authors delineate a concept for the non-invasive spectrophotometric determination of absolute plasma bilirubin concentration. By referencing the pulsatile spectrophotometric signal component of the metabolite of interest (MOI, here: bilirubin) to the pulsatile spectrophotometric signal component of a reference metabolite (MOR, here: water) of known plasma concentration, the absolute MOI concentration can be calculated. Based on Beer-Lambert's law and some reasonable assumptions, the authors developed a theoretical concept for the calculation of MOI concentration. They suggest light of 1200 nm wavelength to measure MOR, 795 nm and 570 nm to measure hemoglobin as correction signal, and 450 nm to measure the MOI. To enhance data quality one could assign several wavelengths to each metabolite. Since in tissue spectrophotometry Beer-Lambert's law does not reflect physiology accurately, it will be necessary to empirically fine-tune the computer algorithms.