 To avoid the logistical difficulties of arterial cannulation and central venous cannulation required for the determination of cardiac output, a relative Blood Flow Index BFI has been proposed. The BFI method is a minimally invasive alternative and was first developed for rapid and repeated bedside estimation of cerebral blood flow. The BFI is derived from a transcutaneously measured NIRS ICG signal and does not require arterial cannulation or the measurement of cardiac output. BFI is a relative measure of blood flow as absolute flow cannot be determined unless arterial ICG concentration is measured. 