Background: Indocyanine green (ICG) elimination tests have been used for over 20 years to assess the hepatic functional reserve (i) before, during and after liver resection and (ii) in the liver transplant setting. Percutaneous pulse spectrophotometric ICG measurement has been developed in recent years and correlates well with the conventional invasive ICG-clearance test. From the practical point of view an ICG plasma disappearance rate (ICG-PDR) >5%/min represents an important prognostic factor after liver resection and seems to indicate hepatic recovery. However, the precision of ICG-PDR in small for size liver remnants (<0.8% of body weight) remains unclear.
Methods: We therefore measured ICG-PDR during the anhepatic phase of orthotopic liver transplantation (OLT) after injection of 0.5mg ICG/kg body weight using a non-invasive finger-clip-sensor (LIMON pulse spectrophotometer).
Results: ICG-PDR values were determined in 20 patients. Two patients had to be excluded from analysis due to instable ICG signals. Median ICG-PDR (n=16, after exclusion of two outliers) was 1.7 (95% confidence interval: 0.8, 2.5) %/min. According to the histogram our results can be subdivided in a group with low (median 0.8; 95% confidence interval: 0.2, 1.0) and high (median 2.5; 95% confidence interval: 1.9, 2.6) ICG-PDR (t-test: p<0.001). A correlation between the low and high ICG-PDR group and patient's gender, age, or bodyweight was not detected. The standardized anesthetic regimen (i.e. volume and drug administration, respiratory management) was similar in all patients. Surgical procedures were not different between the two groups and no association to the individual liver transplant surgeon, to the amount of blood loss, or the presence or absence of a temporary portocaval shunt during the anhepatic phase of OLT was found. No significant differences in terms of postoperative morbidity and the overall length of hospital stay were noticed in the two groups.
Conclusions: Unexpectedly, ICG-PDR values different from zero were detected during the anhepatic phase of OLT. A high ICG-PDR may be the expression of volume and/or ICG dye distribution to a third space through a capillary leak (i.e. due to a perioperative systemic inflammatory response syndrome). A spontaneous decay of ICG or inaccurate non-invasive ICG determination by the LIMON pulse spectrophotometer seems unlikely. Unfortunately, due to potential overestimation of the functional hepatic reserve in small for size liver remnants, real-time ICG-PDR measurement does not appear to represent a reliable tool for the hepatobiliary surgeon to determine the minimally required liver mass during extended liver resections.