Measurement of cerebral blood volume using near-infrared spectroscopy and indocyanine green elimination

Intensive Care Unit and Scottish Liver Transplant Unit, Department of Anaesthetics, Royal Infirmary, Edinburgh EH3 9YW, United Kingdom Methods for measuring cerebral blood volume (CBV) have traditionally used radioisotopes. More recently, near-infrared spectroscopy (NIRS) has been used to measure CBV by using a technique involving O 2 desaturation of cerebral tissue, where the observed change in the concentration of oxygenated hemoglobin is a marker of the volume of blood contained within the brain. A new integration method employing NIRS is described by using indocyanine green (ICG) as the intravascular marker. After bolus injection, concentration-time integrals of cerebral tissue ICG concentration ([ICG] tissue ) measured by NIRS are compared with corresponding integrals of the cerebral blood ICG concentrations ([ICG] blood ) estimated by high-performance liquid chromatography of peripheral blood samples with allowance for cerebral-to-large-vessel hematocrit ratio. It is shown that near infrared; cerebral-to-large-vessel hematocrit ratio; Fahraeus effect; pathlength