FLUOROSCEIN

Fluoroscein, when injected intravenously, rapidly equilibrates throughout the circulation and extracellular fluid, thereby penetrating all perfused tissue.14,15 As the dye is excreted by the kidney, it gradually moves from the extracelluear fluid to the venous system until it is completely eliminated.

Exposure of fluoroscein to ultraviolet light produces a green fluorescence. The clinical use of fluoroscein consists of determining whether tissue fluorescence occurs following intravennous fluoroscein injection. Absence of fluorescence indicates a lack of arterial inflow, whereas prolonged fluorescence suggests venous obstruction. Observation of fluorescence is made most reliably on skin. 16-18

Visible assessments of tissue perfusion can be made following injection of large doses of fluoroscein by inspecting the tissue with an ultraviolet Wood's lamp. Perfused skin flouresces a bright green that slowly fades. Using fluoroscein in this way requires long periods of time between observation periods to permit dye excretion.16

A quantitative fluorimeter can detect and quantitate fluorescence emitted by low concentrations of fluoroscein.15,19,20 The probe of the fluorimeter contains an ultraviolet light source and a sensor that transmits detected fluoroescence to a microprocessor that translates the signal to a number. The quantitation derives from calibration to a standard fluorescent source. This method permits use of small doses of dye and frequent observation.

Fluoroscein rarely causes nausea or allergic reaction. Readings may be variable if the skin examined is pigmented, macerated, or escharotic. Readings are unreliable on new skin grafts and muscle surfaces.

LASER DOPPLER

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