Indocyanine green clearance as a marker of graft function in liver transplantation

Current and Potential Applications for Indocyanine Green in Liver Transplantation

Indocyanine green (ICG) is a fluorescent dye taken up and almost exclusively cleared by the liver. Measurement of its clearance and visualization of its fluorescence make it suitable for a number of potential applications in liver transplantation including assessment of liver function and real-time assessment of arterial, venous, and biliary structures. ICG clearance can be used to assess donor graft quality before procurement and graft metabolic function before transplant using normothermic ex vivo machine perfusion. ICG clearance in the post-liver transplantation period is able to predict recipient outcomes with correlations to early allograft dysfunction and postoperative complications. After absorbing light in the near-infrared spectrum, ICG also emits fluorescence at 835 nm. This allows the assessment of vascular patency after reconstruction and patterns of liver perfusion in real time. ICG perfusion patterns after revascularization are also associated with posttransplant graft function and survival. ICG fluorescence cholangiography is routine in a number of centers and acts as an aid to identifying the optimal point of bile duct division during living donor liver transplantation to optimize safety for both donor and recipient. In summary, ICG is a versatile tool and has a number of useful applications in the liver transplantation journey including assessment of liver function, perfusion assessment, and cholangiography. Further research and clinical trials are required to validate and standardize its routine use in liver transplantation.

An efficient method for measuring plasma volume using indocyanine green dye

Plasma volume (PV) can be an important marker of health status and may affect the interpretation of plasma biomarkers, but is rarely measured due to the complexity and time required. Indocyanine green (ICG) is a water-soluble tricarbocyanine dye with a circulatory half-life of 2–3 min, allowing for quick clearance and repeated use. It is used extensively in medical diagnostic tests including ophthalmologic imaging, liver function, and cardiac output, particularly in critical care. ICG has been validated for measuring PV in humans, however previous work has provided minimal published details or has focused on a single aspect of the method. We aimed to develop a detailed, optimal protocol for the use of ICG to measure PV in women of reproductive age. We combined best practices from other studies and optimized the protocol for efficiency.

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This method reduces the time from blood collection to PV determination to ˜2 h and the amount of plasma required to estimate PV to 2.5 mL (1.5 mL before ICG injection and 1.0 mL post-injection).

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Participant inconvenience is reduced by inserting an intravenous (IV) catheter in only one arm, not both arms.

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Five post-injection plasma samples (2–5 min after ICG bolus) are enough to accurately develop the decay curve for plasma ICG concentration and estimate PV by extrapolation.

Quantitative assessment of hepatic function and its relevance to the liver surgeon

BACKGROUND

Standard evaluation of patients undergoing hepatic surgery has been through radiological and quantitative determination of liver function. As more complex and extensive surgery is now being performed, often in the presence of cirrhosis/fibrosis or following administration of chemotherapy, it is questioned whether additional assessment may be required prior to embarking on such surgery. The aim of this review was to determine the current knowledge base in relation to the performance of quantitative assessment of hepatic function both pre- and post-operatively in patients undergoing hepatic resectional surgery and liver transplantation.

METHODS

An electronic search was performed of the medical literature using the MEDLINE database to identify relevant articles with cross-referencing of all identified papers to ensure full literature capture.

RESULTS AND CONCLUSIONS

The review has identified a number of different methods of dynamically assessing hepatic function, the most frequently performed being through the use of indocyanine green clearance. With the recent and further anticipated developments in hepatic resectional surgery, it is likely that quantitative assessment will become more widely practiced in order to reduce post-operative hepatic failure and improve outcome.

Evaluation of the splanchnic circulation with indocyanine green pharmacokinetics in liver transplant patients

Although indocyanine green (ICG) can be used to estimate cardiac output (CO) and blood volume independently, a recirculatory multicompartmental ICG model enables description of these and additional intravascular factors. This model was used to describe the effect of end-stage liver disease (ESLD) on systemic and splanchnic hemodynamics in patients undergoing orthotopic liver transplantation. ICG disposition was determined during the dissection phase in six patients with ESLD undergoing orthotopic liver transplantation and six healthy adult living liver donors. After injecting ICG, plasma concentrations were obtained for approximately 10 to 12 minutes by noninvasive pulse dye densitometry. The recirculatory model characterizes three distinct intravascular circuits: lumped parallel fast (presumably nonsplanchnic circulation) and slow peripheral (splanchnic) circuits and a central circuit (central blood volume). Mean transit time (MTT) in the fast peripheral circuit was not different in patients with ESLD and controls. However, ESLD resulted in a significant decrease in MTT in the central (0.11 +/- 0.028 [SD] v 0.24 +/- 0.094 minutes in controls; P <.001) and slow peripheral circuit (0.67 +/- 0.41 v 1.37 +/- 0.37 minutes in controls; P <.001) because of increased flows to the central and slow peripheral circuits. These findings are consistent with the described hyperdynamic systemic and splanchnic circulations in patients with ESLD. In conclusion, the ICG model is able to derive estimates of not only blood volume and CO, but also splanchnic hemodynamics under different physiological conditions. This model can be a useful tool to evaluate the effect of pharmacological manipulation of splanchnic hemodynamics.