Precise measurement of cerebral blood flow in newborn piglets from the bolus passage of indocyanine green

Indocyanine green (ICG) is a near-infrared dye that has the potential to be used as a tracer for the minimally invasive measurement of cerebral blood flow (CBF). In order to examine the technique, the arterial and cerebral co ncentrations of ICG were measured in newborn piglets during the bolus passa ge of ICG at normocapnia and two levels of mild hypercapnia. The results we re analysed by applying the Fick principle in both integral and differentia l forms using a linear regression technique to improve the precision of cal culated values of CBF. It was found that the integral method, which has bee n used previously, is particularly sensitive to errors in the time registra tion between the arterial and tissue signals whereas the differential metho d is less so. In addition, the differential method allows the venous outflo w to be calculated which gives further information on the state of the capi llary bed. CBF was 39.7 +/- 4.6 ml 100g(-1) min(-1) at an arterial carbon d ioxide tension (PaCO2) Of 33.0 +/- 2.2 mmHg and increased to 53.7 +/- 9.1 a nd 75.4 +/- 15.2 ml 100 g(-1) min(-1) at a PaCO2 of 42.1 +/- 2.6 and 54.2 /- 3.1 mmHg respectively (mean +/- SD. n = 7). There was no significant cha nge in cerebral metabolic rate for oxygen. validating the value of blood fl ow to an arbitrary scaling factor. When the inspired CO2 fraction was retur ned to zero, calculated CBF returned to baseline with a variation of 7% of the mean, indicating that this technique is highly precise.