Indocyanine Green Tissue Perfusion Monitoring

Methods to reliably predict which cutaneous wounds will heal are unreliable and clinical judgment inadequate. This is a problem for all health care providers and a common dilemma when evaluating patients in the Emergency Department. While capillary blood perfusion of the skin is a recognized requirement for healing, objective methods to reliably quantify this necessary physiological parameter are lacking. In large part, this is due to difficulties visualizing and recording capillary blood flow. Despite technical advances in blood flow imaging the capillary circulation remains poorly characterized. That is, current methodology can only image medium-to-large caliber vessels, not the small capillaries. The investigators hypothesize that with new technology, objective assessment of capillary flow can be achieved with fluorescence-mediated photoplethysmography (FM-PPG) methodology, and this evaluation can be used to objectively determine which wounds will heal promptly versus require adjunctive interventions.

FM-PPG is currently being used clinically in clinics worldwide as a way to image blood flow, but the apparatus provides only a relative measurement. Thus, this investigation is Observational in nature and not Interventional. With repeated evaluations over weeks, current FM-PPG allows an assessment to be made on whether wound conditions are improving. The investigators have a device containing new imaging software which, in theory, can offer precise quantification of capillary blood flow. If true, a single measurement may provide the data necessary to predict which patients are in danger of not healing and thus requiring aggressive, and at times expensive or painful interventions and - even worse - limb amputations. This protocol is to test proof-of-concept by first evaluating cutaneous capillary follow in 30 normal, healthy individuals and then 30 individuals presenting for treatment with a variety of skin wounds to a clinic.

FM-PPG methodology requires intravenous injection of a small amount of a fluorescent dye, indocyanine green (ICG). ICG is an FDA-approved agent that has been safely used in over 4000 patients. The area of skin to be measured is positioned below a camera and low-power laser instrument to take fluorescent pictures. The ICG is dissolved in sterile salt water for injection and about one and one half tablespoons injected into a vein. Typically, the measuring sequence consists of obtaining fluorescence images at the rate of approximately 30/second during a period of about 15 seconds. Following acquisition of the initial transit angiogram sequence, several additional 15-second-long image sequences are then acquired during the next half-hour, but without any additional injections. At about 60 seconds following dye injection, about two teaspoons of venous blood is withdrawn. This blood is used in the laboratory to determine the ICG dye concentration as a verification of the concentration determined by the camera images as part of the FM-PPG software algorithm (circulating dye concentration is needed in calculation of quantitative blood perfusion).

Since this study will be the first to employ a methodology capable of acquiring absolute tissue blood perfusion data from multiple subjects, there exists no database to indicate the normal range of variation in skin tissue perfusion that occurs in normal subjects. Since abnormal perfusion cannot be clearly recognized until the normal range of variation has been established, the first 30 subjects will be normal individuals. Then the following 30 subjects will be patients undergoing wound healing therapy.