A new method for the measurement of cerebral blood volume and total circulating blood volume using near infrared spatially resolved spectroscopy and indocyanine green: application and validation in neonates.

A new technique known as tissue dye densitometry (TDD) has been developed to simultaneously measure cerebral blood volume (CBV) and total circulating blood volume (TCV) using near infrared (NIR) spatially resolved spectroscopy (SRS) and the injection of indocyanine green (ICG). Using a medical NIR spectrometer with SRS capability (NIRO-300, Hamamatsu KK), a new parameter is calculated known as the ICG Hb index (IHI), which represents the ratio of ICG concentration to Hb concentration in tissue. Acting as a tracer, ICG is cleared by the liver over 15 min, providing a change of tracer concentration (DeltaCICG,tis), which allows the calculation of the total Hb concentration in tissue (tcHb) using the equation: tcHbtis (micro molar) = DeltaCICG,tis/DeltaIHI. The CBV can subsequently be calculated from tcHbtis given the absolute Hb concentration in blood (g/dL), from which the ICG concentration in blood (DeltaCICG,bl) is obtained. By back-extrapolating the DeltaCICG,bl curve to the peak time, the initial ICG concentration in tissue blood (C0ICG,bl) can be found and TCV can then be calculated. The TCV of 17 neonates were measured using the TDD technique and for comparison using the previously reported fetal Hb dilution technique (FHD). The mean TCV measured by the FHD and TDD techniques were 70.19 +/- 13.73 mL/kg and 70.80 +/- 32.54 mL/kg. The Bland Altman plot showed that the bias was 0.61 +/- 34.34 mL/kg and limits of agreement (2 SD) were -68.07 mL/kg and 69.30 mL/kg. The agreement is limited and the TDD technique needs further validation and development for use in a clinical environment.