Non-invasive liver monitoring in the critically ill: plasma disappearance rate of indocyanine green (ICG-PDR)

In contrast to pulmonary, cardiovascular, renal and neurological function, liver function is not easily monitored in the critically ill. Traditionally, the degree of liver dysfunction is assessed by using biochemical tests - transaminases, bilirubin, albu- min and prothrombin time. These are static tests, they only assess the presence of hepatobiliary injury and tend to respond late to damage. Moreover, they do not track organ perfusion, oxygenation or the functional capacity of the liver. Over the last decades, several dynamic tests have been developed that use hepatic clearance of tracer substances (indocyanine green) or metabolic capac- ity for certain drugs (lidocaine) as a measure of hepatic function. Recently, automatic non-invasive devices have become available which promise dynamic assessment of liver function based on indocyanine green plasma disappearance rate (ICG-PDR). This review focuses on the principles, limitations and clinical use of non-invasive liver monitoring with ICG-PDR in the critically ill. Although there is clinical evidence in favour of the prognostic use of ICG-PDR in critically ill patients, no interventions studies exist using ICG-PDR to titrate therapy. Finally, we also briefly describe some other non-invasive techniques in this context includ - ing the monoethylglycinexylidide (MEGX) test, Doppler ultrasound flowmetry and scintigraphy.