Biodistribution of indocyanine green in a porcine burn model: light and fluorescence microscopy.

Background: Infrared-excited fluorescence of intravenously administered indocyanine green (ICG) is being used as a method of early determination of burn depth. Methods: Fluorescence microscopy and tissue fluorescence were recorded in a porcine burn model and correlated to burn severity and age. Results: Recently placed superficial burns show significant fluorescence compared with adjacent normal tissue as a result of a strong inflammatory reaction in the superficial dermis with minimal vascular occlusion. The magnitude of the inflammatory reaction decreases with time. For deeper burns, vascular occlusion prevents transport of ICG into the burn and the intensity of ICG fluorescence in burn eschar is negligible. Conclusion: The intensity of ICG fluorescence measured at the surface of the wound for burns of similar age was shown to decrease exponentially with the depth of the burn. The enhanced fluorescence of partial-thickness burns is attributable to increased permeability, and the decreased signal associated with deeper injuries is attributable to vascular occlusion. These results suggest that it is possible to differentiate burns that will heal spontaneously with minimal granulation from those that will not by measuring the intensity of ICG fluorescence.