Does Indocyanine Green Accurately Measure Plasma Volume Early After Cardiac Surgery?

Abstract

Overestimation of indocyanine green-derived plasma volume can occur in the presence of generalized capillary protein leakage. This overestimation was examined early after cardiac surgery by using the simultaneous measurement of the initial distribution volume of glucose. We suggest that overestimation of the traditional dye dilution method is negligible, but apparent over- or underestimation of pulse dye densitometry-derived plasma volume cannot be negligible.

Technical and physiological background of plasma volume measurement with indocyanine green: a clarification of misunderstandings

“…For the plasma method (14,15,20,29), only one single venous cannula, inserted into a cubital vein, is needed. After calibration of the system (measurement of the specific extinction in two 5-ml samples of the patient's plasma containing ICG at 2 artificially generated concentrations), the dye (0.25 mg ICG/kg body wt) is injected into the patient's circulation at t 0 .…”

“…The point is to correctly interpret this value to establish the "real" PV, and this is obviously a serious problem for some investigators (20,23,29): PV derived via ICG-DT was, e.g., "checked for correctness" by calculating RCV from PV and Hct LV and expecting this RCV derived from ICG (RCV ICG ) to be constant in the absence of any bleeding or transfusion if the ICG-DT was consistent. In other cases, PV derived from ICG-DT (PV ICG ) was expected, as a proof for consistency of the method, to be constant before and after an intervention (e.g., induction of general anesthesia or volume loading).…”

“…The distribution space can be calculated from this concentration and the amount of dye injected, and the investigator normally assumes that this space represents PV. However, several reports questioned the accuracy of the ICG-DT for several reasons (20,23,29). This report aims to summarize the knowledge about the ICG-DT, including the physiological background, to forestall profound misunderstandings of a well-established method for direct measurement of total PV.…”

Advantages of fluorescence over diffuse reflectance measurements tested in phantom experiments with dynamic inflow of ICG

“…Indocyanine green (ICG) is a relatively non−toxic dye [4] which is applied as an optical marker for liver func− tion testing [5][6][7] in ophthalmology [8] and for assessment of hemodynamic parameters [9][10][11]. In experiments carried out on animals it was also shown that the ICG monitoring may allow for evaluation of cerebral blood volume [12].…”

Enhanced photostability of ICG in close proximity to gold colloids

“…1). ICG was chosen because of widespread use in medical testing [17][18][19] and growing use as a contrast agent in optical tomography [20][21][22]. We speculated that the long wavelength absorption and emission wavelengths of ICG may minimize quenching due to the gold absorption while still increasing the photostability.…”