The influence of congestion and ischemia on survival of an experimental vascular pedicle island flap

Effects of arterial blood supply and venous return on multi-territory perforator flap survival

This study aimed to design arterial ischemic and venous congested areas on the same multi-territory perforator flap, assessing the effects of arterial blood supply and venous return on flap survival. Totally 68 rats were randomly divided into the experimental (Exp) and control (Con) groups. In the Exp group, flaps were based on left superficial epigastric artery and right superficial epigastric vein. In the Con group, flaps were based on the left superficial epigastric artery and vein. Immediate postoperative ink-gelatin angiography, epidermal metabolite levels detection, tissue edema measurement, survival rate evaluation in half of the flaps and average microvessel density assessment were performed. Blood in the Exp group flowed through most angiosomes, but only flowed around pedicled vessels in the Con group; metabolite levels of left halves in the Con and Exp groups were comparable with those of right halves. Angiosomes with high water contents occurred in the Exp group. Survival rates of left halves in the Con and Exp groups were higher than those of right halves, and more microvessels were found in the left ventral areas of both groups compared with the right ventral area in the Exp group. These findings revealed that on the same multi-territory perforator flap, arterial blood supply, affected by venous return, is a prerequisite for flap survival.

The rat groin flap model redesigned for evaluating treatment effects on ischemia-reperfusion injury

BACKGROUND

Although there is a wide application of the rat extended groin flap (epigastric skin flap) in studying different clinical issues, inconsistency arises between studies because many parameters of the extended groin flap have not been well defined.

MATERIALS AND METHODS

The flap is based on the superficial inferior epigastric vessels, which give into a lateral and a medial branch distally. Herein, three steps were taken to redesign this model: First, the ventral vascular anatomy was visualized through an imaging study to determine the flap borders. Second, different ischemic durations were induced on five groups of Lewis rats (n = 5 in each group) by clamping the femoral artery; group 1 (sham group) received no ischemic insult after elevation and was immediately repositioned, and groups 2, 3, 4, and 5 received 12-, 14-, 16-, and 18-hour ischemia, respectively. Percentage of necrosis area was measured after 5 days. Third, the redesigned groin flap model was tested with the ischemic postconditioning for validation.

RESULTS

The flap borders were determined such that both branches of the superficial inferior epigastric vessels were always included to ensure blood supply consistency. As the 14-hour ischemia induced the least variation in necrotic area on rats, it was chosen for further studies. In addition, ischemic postconditioning after 14-hr ischemia resulted in significant reduction of necrosis in this model.

CONCLUSIONS

We have redesigned the extended groin flap model with better-defined borders and consistent vascular anatomy. The ischemia duration was calibrated with predictable necrosis pattern and the practicality was demonstrated. With this model, precise assessment of treatment efficacies on ischemia-reperfusion injury could be achieved in future studies.

Delay in Neurovenous Flaps

The objective of this study was to examine the effects of the standard surgical delay in the flaps based on the cutaneous branches of the vascular axis around a superficial sensory nerve. The delay procedure was experimentally tested in rats and subsequently used in patients. In the experimental study, the survival of a delayed inferior epigastric neurovenous flap was compared with that of a nondelayed inferior epigastric neurovenous flap. One type of clinically applicable delay pattern (standard bipedicled technique) was employed. A 3 x 3 cm flap was raised in 20 female Wistar rats assigned randomly to 2 groups. Each group consisted of 20 flaps. The standard bipedicled delay pattern increased the percentage survival of the delayed inferior epigastric neurovenous flap. The survival percentage of the delayed flaps was 59.8 +/- 185.0 (P < 0.5). The histologic findings of the skin revealed that our delay procedure enhanced the perfusion of the flap by dilating the arterial network. Stimulated by our experimental findings, we used the island bipedicled surgical flap delay or combined strategic-standard delay in the distally pedicled sural flap successfully on 9 cases.

Management of flaps with compromised venous outflow in head and neck microsurgical reconstruction

Microvascular tissue transfer has become an indispensable procedure for head and neck reconstruction. Although remarkable progress has been made technically, anastomosed vessel occlusion is still a serious complication. Even with technically skilled microsurgeons, anastomosed vessel occlusion occurs because the technique is not the sole prophylaxis against thrombosis in microsurgery. Therefore, to minimize the possibility of an unfavorable result in microsurgery, microsurgeons must be familiar with management options for a vascular compromised flap. Most investigators have agreed that venous obstruction occurs more often than arterial obstruction. Here, we reviewed the published literature on the salvage of venous compromised flaps from the viewpoints of surgical correction, including reanastomosis and catheter thrombectomy, and nonsurgical procedures, such as a medicinal leech, hyperbaric oxygen, and thrombolytic therapy.

Effect of hyperbaric oxygen on pedicle flaps with compromised circulation

The effect of hyperbaric oxygen (HBO) on the survival rate of experimental rat pedicle island flaps with arterial, venous, and combined arteriovenous insufficiency was evaluated. Forty male Wistar rats with pedicle island flaps were divided into four groups with different types of vascular status. Another 40 male Wistar rats, also divided into four groups, were reconstructed in the same manner, but were also exposed to HBO. The results were evaluated using a laser Doppler flowmeter and an estimation of the length of the surviving tissue of the flaps. In evaluations using Kruskal-Wallis test, there was a significant difference in the survival tissue length and mean LD flows among our four untreated groups (P < 0.05). We considered the experimental model defined by Tzusuki and colleagues suitable for our study. Using a Mann-Whitney test, the differences in flap tissue survival length between each type of vascular insufficiency of HBO-treated and untreated groups was significant (P < 0.05). This finding indicates that the survival length was directly improved by the HBO treatment for all type of vascular insufficiency. HBO treatment increased the percentage of survival length and mean LD flows of axial pattern skin flaps with all type of vascular insufficiency. This effect, however, was greatest in the arterial insufficiency flaps.

Estudo da isquemia e reperfusão em retalhos cutâneos de ratos

INTRODUÇÃO: Múltiplos fatores têm sido implicados na patogênese da lesão de isquemia/reperfusão da pele, incluindo as espécies reativas de oxigênio. OBJETIVO: Estudar a lesão de isquemia/reperfusão em retalhos cutâneos de ratos avaliando os níveis teciduais do malonildialdeído (MDA) e xantina oxidase (XO). MÉTODOS: Foram utilizados 8 ratos Wistar, com peso entre 300 - 400g, sendo confeccionados 2 retalhos epigástricos por animal (controle e experimento), um deles submetido à 16h de isquemia (RI) seguida de 45 min de reperfusão (RR) e o outro controle (RC). Foram colhidas 3 biópsias de pele dos retalhos (RC, RI, RR) e encaminhadas para dosagem de MDA e XO. RESULTADOS: A análise bioquímica mostrou aumento significativo dos níveis teciduais de MDA e XO após a reperfusão em relação aos retalhos controles. CONCLUSÃO: Retalhos epigástricos de ratos submetidos à 16h de isquemia e 45min de reperfusão apresentam elevação dos níveis teciduais de MDA e XO, caracterizando a lipoperoxidação da membrana celular.

The rat ventral island flap: a comparison of the effects of reduction in arterial inflow and venous outflow

The relative importance of reduced arterial inflow versus reduced venous outflow in determining flap necrosis remains undefined, even though this is critically important in understanding the effects of pharmacologic agents on flap survival. By means of a rat bipedicled ventral island flap, the amount of random flap necrosis was examined in four experimental groups: (1) unilateral arteriovenous ligation (n = 19), (2) unilateral vein ligation (n = 20), (3) unilateral artery ligation (n = 20), and (4) alternate side vein and artery ligation (n = 18). No necrosis occurred on the side of the vein ligation in groups 2 and 4, indicating that independently reducing venous outflow does not cause flap necrosis. A predictable necrosis occurred ipsilateral to artery ligation in groups 1 (37.63 +/- 17.34 percent), 3 (32.74 +/- 17.32 percent), and 4 (15.70 +/- 9.86 percent). These data indicate that the rat ventral island flap is more sensitive to a decrease in arterial inflow than to a decrease in venous outflow. This model may therefore be useful in clarifying the effect and determining the mechanism of action of pharmacologic agents that alter flap survival.

The influence of arterial insufficiency and venous congestion on composite graft survival

A rabbit auricular amputation model was used to study the relative effects of arterial insufficiency (AI) and venous congestion (VC) on composite graft survival. The percentage of graft survival was significantly greater for the AI group (45.8%) than for the VC group (15.9%) 2 weeks postoperatively. The percentage of graft survival at 3 weeks for the VC, AI, and noligation groups were not statistically different. All three groups were statistically different from the control group, which had both the central artery and vein ligated. The VC group also exhibited significantly more graft edema, as measured by maximal graft thickness, than the other three groups. The impact of AI and VC on composite graft survival is investigated and discussed. These results suggest that venous congestion is more detrimental to early graft survival than arterial insufficiency.

Hemodynamic variations between end-to-side and end-organ flap systems

This study aimed to evaluate microcirculatory differences between anatomic arrangements of the intact side flow and the end flow systems. The cremaster muscle tube-flap model was employed. Fifty male Sprague-Dawley rats were studied in two experimental groups of 25 animals each. The end-to-side vascular system was compared with end-organ flaps during acute (6 hours) and chronic (1, 3, 7, and 14 days) observation periods. Standard microcirculatory measurements were taken in all groups including vessel diameters, red blood cell velocities, and capillary densities. End-to-side flaps presented with stable flow hemodynamics over a 14-day period. In end-organ flaps we found acute venous congestion, alterations in arterial and venous flow velocities, and a significant decline in capillary perfusion.

The effects of extended perioperative pentoxifylline on random skin flap survival

PURPOSE

This study was designed to determine the effects of long-term perioperative pentoxifylline administration on random skin flap survival in an appropriate animal model. A secondary objective was to document bioavailability of pentoxifylline in the animal model by measuring blood levels of parent compound and metabolites at regular intervals and comparing these to levels measured in humans.

MATERIALS AND METHODS

A randomized control study of the effects of oral pentoxifylline on the survival of "random" skin flaps was conducted at the animal care facility of an academic tertiary referral center on six randomly selected Yorkshire pigs. Oral pentoxifylline was administered daily to four pigs for 3 months, and two pigs received placebo. Pentoxifylline blood levels for each experimental animal were measured after 4, 8, and 12 weeks of daily dosing. Blood viscosity, fibrinogen, and hematocrit were measured for each of the six animals on day 1, day 30, day 60, and day 91. On day 91, 12 surgical random skin flaps were elevated on each of the six animals and immediately sewn back in the donor bed. Pentoxifylline dosing was continued for 2 weeks, and placebo was continued in control animals. On postoperative day 15, all animals were killed and all flaps were measured individually for area of viability. The outcome measure was the detection of statistically significant increase in survival area in skin flaps of those animals administered perioperative pentoxifylline.

RESULTS

No significant augmentation of flap survival was noted in experimental animals when compared with those in the control group; no significant difference was noted between or within groups of experimental animals. Pentoxifylline and metabolite blood levels in all experimental animals at every interval were noted to be comparable to those documented in human studies; metabolite concentrations conformed to expected patterns as observed in humans. No significant alterations of blood viscosity, fibrinogen, or hematocrit were measured in the experimental animals when compared with those in the control group. The only animal showing mean flap survival outside the 95% confidence interval was one in the control group.

CONCLUSION

No augmentation of random skin flap survival could be shown in the pig model after a 3 month regimen of daily oral pentoxifylline. Blood levels of pentoxifylline in experimental animals were compared with those documented in humans. No alteration of blood viscosity, fibrinogen, or hematocrit was noted in any of the experimental animals when compared with each other or with those in the control group.

The oblique rat groin flap

Neovascularisation from the bed can result in the partial survival of failing rat groin flaps. This can interfere with the interpretation of pharmacological augmentation and ischaemia experiments. We describe the development of a modified rat groin flap which utilises the inguinal fat pad to diminish the effects of the bed on the skin component of the flap. The behaviour of this model is compared to that of standard rat groin flaps and flaps which have had polythene sheeting placed under them.