Noninvasive ICG clearance test for estimating hepatic blood flow during halothane and isoflurane anaesthesia

The purpose of this study was to estimate hepatic blood flow during halothane (HAL) or isoflurane (ISO) anaesthesia with the noninvasive indocyanine green (ICG) clearance test. Twenty-four ASA status I adult patients, scheduled for elective surgery without liver disease, were allocated into four groups. Before surgery, ICG clearance was measured twice in patients before and after 1, 2 MAC HAL-N2O, 1 and 2 MAC ISO-N2O anaesthesia by ICG clearance meter (Sumitomo Electronics, Japan). This method eliminates the blood sampling and delay of the conventional ICG test. The ICG clearance is displayed in two indices: K (ICG disappearance rate) and R15 (ICG retention rate 15 min after 0.5 mg.kg-1 ICG injection). Indirect blood pressure and heart rate were measured simultaneously. Mean arterial pressure (MAP) decreased by 27, 22 and 29% with 2 MAC HAL-N2O, and with 1 and 2 MAC ISO-N2O groups, respectively (P < 0.05). The ICG clearance was less (P < 0.05) in the 2 MAC HAL-N2O group (K, 0.087 min-1) than with either awake (K, 0.131 min-1) or other groups (K, 0.114 and 0.144 min-1, in the 1 MAC HAL and ISO-N2O groups, respectively) in spite of a similar degree of the depletion of MAP in 2 MAC ISO-N2O group (K, 0.124 min-1). We conclude that isoflurane has a more favourable effect on liver circulation than does halothane.