David A. Brousseau

Assessment of neovascularization and timing of flap division.

These studies were undertaken to determine if perfusion fluorometry can provide an accurate, reliable means of monitoring neovascularization and predicting optimal time of flap division. An animal model was developed that permitted daily assessment of neovascularization of the flap using fluorescein injections and the fluorometer. An increase in fluorescence of the pedicle-occluded flap of approximately 12 percent the normal skin fluorescence was associated with 100 percent flap survival. This occurred after only 4 days in the rat. Fluorometry proved valuable in the evaluation of clinical flaps. The fluorescence of flaps during pedicle occlusion was observed to increase with each successive fluorometric evaluation performed at 3- to 7-day intervals. It appears that flaps after pedicle occlusion exhibiting at least 25 percent of the fluorescence of normal skin will tolerate pedicle division. Based on the neovascularization studies of the clinical flaps, all pedicles were severed earlier than originally anticipated. Two cross-leg flaps were successfully divided after 11 days. Quantitative assessment of serial fluorescein injections allows reliable evaluation of neovascularization in clinical interpolation flaps and is useful in the timing of flap division.

Quantification of fluorescein distribution to strangulated rat ileum

Following various periods of strangulation, the fates of intestinal segments were predicted by standard clinical criteria and visual (Woods lamp) and fluorometric (perfusion fluorometer) assessment of fluorescein distribution. With fluorometry, a means of quantifying fluorescence transmitted via a fiberoptic light guide, the delivery and removal of fluorescein were monitored and analyzed. If either was restricted significantly, tissue death was predicted. Analysis of computerized graphic patterns or simple interpretation of fluorometric readings at two time points predicted tissue fate with 98% accuracy and a 93% negative predictive value. Woods lamp evaluation had only a 53% accuracy and a 33% negative predictive value, while standard clinical criteria had an 81% accuracy and a 53% negative predictive value. Fluorescein leakage in segments which suffered significant endothelial damage provided staining patterns that incorrectly suggested viability. By monitoring elimination as well as uptake of dye, fluorometry provided much greater discrimination than did Woods lamp inspection in this setting. In addition, fluorometry was readily repeatable within minutes, as fluorescence remaining from a previous injection could be subtracted from new, postinjection values.

Vascular Island skin-flap tolerance to Warm ischemia: an analysis by perfusion fluorometry

Fiberoptic perfusion fluorometry and assessment of ultimate viability were used to analyze the tolerance to warm ischemia of rat vascular island skin flaps. Both acute flaps and flaps raised 24 hours previously and then reraised were subjected to 0 (control), 6, 8, 10, and 12 hours of vascular pedicle clamping. Following clamp release, serial fluorometry documented the progressive delay in effective reflow resulting from extended periods of ischemia. Fluorometry, furthermore , suggested that flaps constructed 24 hours previously had an improved hemodynamic status with a significantly reduced period of poor reflow following clamp release. The improved hemodynamics were associated with increased viability, confirming the increased tolerance of 24-hour-old flaps to warm ischemia.

Fluorometric assessment of skin flap viability in the rat: effect of radiation therapy

The fluorescein test is widely used to assess perfusion in skin flaps but tends to underestimate skin viability when visual inspection under ultraviolet light is employed. Fiberoptic dermofluorometry, which has recently been introduced, more accurately assesses fluorescein distribution in skin flaps than does visual inspection. Viability of the back flap in rats receiving ionizing radiation was evaluated by dermofluorometry. This technique was highly accurate in predicting viability and has great applicability for studying blood flow in irradiated tissues.

Intravenous nitroglycerin as a means of improving ischemic tissue hemodynamics and survival.

The effects of intravenous nitroglycerin infusion on experimental skin flap survival and fluorescein dye kinetics were studied in animals. Perfusion fluorometry was utilized to examine changes in flap hemodynamics and viability. An improvement in skin flap survival was found in the nitroglycerin-infused animals, whether the nitroglycerin was initiated 30 minutes before or 30 minutes after flap elevation. Dye elimination in the flap appeared to be significantly improved with the drug therapy, indicating an improvement in flap blood flow with nitroglycerin.

Fluorometric prediction of successful amputation level in the ischemic limb.

The present study was undertaken to compare fluorometric documentation of fluorescein dye delivery with the standard means of determining the level at which an amputation should be performed in the dysvascular extremity. Thirty-nine patients underwent lower-extremity amputation at the level determined by the surgeon based upon physical examination, angiography, segmental pressure indices, and/or pulse volume recordings. In addition, fiberoptic fluorometry was performed preoperatively. After intravenous administration of sodium fluorescein (4-8 mg/kg), fluorometric readings were obtained by placing the fluorometers light guide on 126 reading sites. Fluorometric findings were evaluated retrospectively, and therefore did not influence the surgeons decision. Of the 39 amputations performed overall, only 26 healed. The accuracy of the standard criteria was lowest for the 20 below-ankle amputations, where only 12 cases healed. Alternatively, fluorometric indices separated healing from nonhealing sites in 36 of the 39 cases and in 18 of the 20 below-ankle amputations. Overall, healing sites averaged 94 percent of the fluorescence of the healthy reference area, while nonhealing sites averaged only 29 percent. We conclude that fluorometry should prove to be a valuable adjunct in the assessment of the dysvascular extremity. It uses a low dose of dye, is easy to perform, and is readily repeatable.

A new technique for evaluating cutaneous vascularity in complicated conjoined twins

Ischiopagus tripus conjoined twins were recently encountered. All organ systems were thoroughly evaluated using radiographic, angiographic, radionuclide, and CT imaging techniques. None of these studies were capable of accurately assessing the vascular territories of the skin at the level of the pelvis, the most critical area in terms of separation. Qualitative visual assessment of tissue fluorescein delivery under ultraviolet illumination is subject to subjective errors. Perfusion fluorometry is a recently developed technique whereby tissue fluorescence can be quantitated over time in very small amounts, even with repeated injections. In these conjoined twins, using sequential fluorescein injections in each twin, it was possible to accurately determine which portions of the pelvis and the shared leg belonged to which twin and exactly where the skin incisions should be made. Additionally, during operation it was possible to accurately predict the viability of skin flaps used for closure. Both twins survived. This is the first time it has been possible to accurately assess vascular territories of the skin in a complicated form of conjoined twinning. The technique is also useful in the evaluation of flow patterns in various other parts of the body.

The Effects of a Topical PGE2 Analogue on Global Flap Ischemia in Rats

The present study evaluated the ability of DHV-PGE2ME, a topically effective 16-vinyl prostaglandin E2 analogue, to improve the tolerance of skin flaps to a period of ischemia. DHV-PGE2ME and placebo were applied to bilateral island flaps on 70 anesthetized rats; then the vascular pedicle of each flap was clamped for 10 hours. Treated flaps evidenced significantly better reperfusion, as documented by quantification of fluorescein dye delivery at 90 minutes after clamp release, and they had significantly greater ultimate viability (p < 0.05, by ANOVA). While less than 3 percent of untreated flaps survived, those treated with 1.75 and 17.5 μg/cm2 of drug evidenced 76 and 86 percent survival, respectively. Treatment of a given flap did not affect its contralateral mate, since there was no evidence of a systemic effect. Especially since its effect can be limited to the site of application, DHV-PGE2ME should be valuable for the treatment of compromised perfusion in a variety of settings.

Fluorometric documentation of increased cutaneous blood flow after topical application of a PGE2 analog in man

The present study employed fiberoptic fluorometry, a noninvasive means of documenting delivery and removal of fluorescein dye, to evaluate the local circulatory changes elicited by topical application of DHV-PGE2 ME, an investigational PGE2 analog. On Day 1, inactive vehicle was applied to a 5 X 4 cm study site on each thigh of healthy volunteer subjects (n = 12). Symmetrical perfusion was confirmed by similar determinations of dye delivery and removal at each site. On Day 2, DHV-PGE2 ME, 30 or 120 micrograms, was applied to one site while inactive vehicle again was applied to the other. After administration of 120 micrograms in a petrolatum vehicle, fluorometry detected a pronounced increase in nutritive perfusion. There was significant acceleration of dye delivery and removal (p less than 0.05 by ANOVA). Less pronounced changes were noted after the lower dose of DHV-PGE2 ME and when the drug was applied in a triethyl citrate vehicle. The local circulatory changes were not accompanied by systemic effects; there were no changes in vital signs or in fluorometric indices at remote sites.

Fluorescein elimination as a measure of island flap perfusion.

The fluorescein test has been used as a means of assessing flap viability for almost 40 years. This study was performed in an attempt to determine if recording of the elirnination of dye—combined with dye uptake measurement—could provide reliable and consistent monitoring of island flap perfusion.