Rat Epigastric Flap Research Articles

Recipient bed vascularity and the survival of ischaemic flaps

The purpose of this study was to identify the length of the ischaemic period required to induce the ‘no-reflow’ phenomenon in a rat epigastric flap on an avascular recipient site. The vascularity of the recipient bed may affect flap survival in the early postischaemic stage after flap transfer. Initially, we designed epigastric flaps in 300–350 g Sprague-Dawley rats and separated the rats into four groups of 5 rats each (total 20 rats). In groups 1, 2, 3, the flaps were made ischaemic for 1 hour, 6 hours and 10 hours, respectively, by temporarily clipping the epigastric artery and vein. In group 4, the epigastric artery and vein were divided to create permanent ischaemia. In groups 1, 2 and 3, ischaemia was ended by removing the clips. After the ischaemic flaps were reperfused, their viability was studied by measuring the flap survival rate at postoperative day 7. Flap survival was studied by direct observations, laser Doppler flowmeter measurement of flap blood flow, histopathology, and carbon particle perfusion of the flap vasculature. Ischaemic flaps of groups 1 and 2 recovered almost completely after reperfusion due to the short period of ischaema. In a second series of experiments, in order to evaluate the contribution to flap survival of the recipient vascularised bed, another four groups of epigastric flaps (of 5 animals each, using the same time periods as above) were raised and a piece of Biobrane was interposed between the flap and the recipient bed before the flap wound was closed, to eliminate all nutrient supply from the recipient bed. The results showed that the combined effect of the reperfused flap vasculature plus the metabolic contribution of the recipient bed significantly ( P < 0.01) increased the extent of flap survival of the 6- and 10-hour ischaemic flaps as well as the divided pedicle flaps, which were never reperfused. An absolute ‘no-reflow’ rat model flap for further flap salvage studies was also developed.

Calcitonin gene-related peptide in experimental ischemia. Implication of an endogenous anti-ischemic effect.

Ischemia resulting from flap harvesting and vascular manipulation during microsurgery may be responsible for flap ischemic sufferance and, ultimately, necrosis. Recently, the regulatory role of the sensory nervous system in ischemia has attracted much interest. Calcitonin gene-related peptide (CGRP), a neuropeptide, is a naturally occurring vasodilator with no constrictive effects. In the present study, we developed a model of partial, chronic ischemia in the rat epigastric flap and investigated the effects of ischemia on concentrations of CGRP-like immunoreactivity (-LI) in ischemic skin and in different regions of the rat brain (striatum, hippocampus, pituitary, hypothalamus, and frontal and occipital cortex). A neurovascular island flap based on the superficial epigastric vessels was raised in 10 animals. Ischemia of the flap was obtained by ligating the feeding artery so that the blood flow was reduced to 25% of the normal circulation. An electromagnetic Doppler positioned on the artery was used to monitor the blood flow reduction. Ten nonoperated animals were used as controls. Ten days after the operation, CGRP-LI was significantly increased in five of six brain regions analyzed (striatum excepted). Significantly decreased concentrations of CGRP-LI were found in seven ischemic flaps, as opposed to the control group. In the remaining three flaps, no significant changes in CGRP concentration were observed. The highest blood flux values (detected using a laser Doppler) in the flaps correlated positively with the highest concentrations of CGRP-LI in the flap tissue. The results of the present study suggest that endogenous CGRP may be involved in the adaptive response to ischemia.

Age and tolerance to secondary ischemia in rat epigastric flaps.

The use of microvascular procedures is increasing as the population continues to age. The purpose of this study was to observe the survival of skin flaps after ischemic injury. Skin flaps (n = 50) underwent either 3 hours of primary (1 degree) or secondary (2 degrees) venous occlusion in young (2-3 mo) and old (18-22 mo) rats. Skin flap survival was assessed on postoperative day 7. Survival rates for young and old after 3 hours of 1 degree ischemia was 100% and 90% (ns). Survival rats for young and old after 2 degrees ischemia were 67% and 47% (ns).

Leeches: controlled trial in venous compromised rat epigastric flaps

Leeches were studied for their efficacy to improve survival of venous compromised rat skin flaps. In 22 rats, bilateral epigastric island flaps were created and subjected to 6 h of venous occlusion. One flap in each animal was randomised to leech treatment, while the contralateral flap served as its own control. Flap survival, leech feeding time, weight gained by the leech and bleeding time from leech bites were measured. The area of flap survival was significantly increased in leech treated flaps compared to contralateral controls (n = 22 pairs, p = 0.03; Wilcoxon signed rank test). Weight gained in the feeding leech averaged 1.3 ± 0.2 g (n = 18). Leech feeding time was 107 ± 13 min (n = 18). Bleeding time from each leech bite averaged 79 ± 12 min (n = 18). Hence, the extent of flap necrosis resulting from venous impairment can be partly diminished by leech treatment until definitive surgical venous revascularisation.

A Biochemical Study of Acute Ischemia in Rodent Skin Free Flaps with and Without Prior Elevation

Elevation of a vascular island flap 24 hours before an ischemic insult (prior elevation) has been shown to significantly increase flap survival, and to decrease blood thromboxane levels, compared with acutely ischemic flaps. The current study considered whether prior elevation causes other biochemical alterations that could be beneficial for flap survival. Tissue levels of adenosine triphosphate (a major tissue energy store), superoxide dismutase (a major defense against free radicals), xanthine oxidase (an enzymatic source of free radicals), and edema were measured. Rat epigastric flaps, with or without prior elevation, had 10 or 12 hours of acute ischemia. Biopsies were taken at 0, 12, or 24 hours after reperfusion. Skin from flaps with no ischemia (control flaps) or control skin was harvested at the same times. Acutely ischemic flaps had significantly lower levels of adenosine triphosphate and less edema than those in prior elevated ischemic flaps after 12 hours of ischemia (both, p less than 0.05). Superoxide dismutase and xanthine oxidase did not vary significantly. It is not clear whether the increased adenosine triphosphate level in prior elevated flaps is the cause or the result of increased tissue viability. Prior elevation did not alter free radical mechanisms. Furthermore, prior elevation was beneficial for flap survival despite increased edema.

Non-suture external cuff techniques for microvascular anastomosis

Microvascular anastomosis can be achieved by eversion of the upstream vessel and over an external cuff and insertion of this into the downstream vessel. This technique, first described in 1900, was initially tested in 13 rat femoral vein anastomoses using small polythene cuffs. Two anastomoses failed and 11 were patent at 7 days. After control studies, in 16 rat epigastric flaps the femoral vein in the vascular pedicle was divided and anastomosed using an external cuff. Thirteen flaps survived. The principles underlying this method appear sound, and form the basis for microvascular anastomotic devices currently being developed.

Preischemic Flap Washout and Its Effect on the No-Reflow Phenomenon

Preischemic perfusion washout with an acellular physiologic solution delays the no-reflow phenomenon and improves tissue survival in rat epigastric free flaps following 18 and 24 hours of normothermic ischemia. This implies that stagnating blood may be a causative agent in the no-reflow phenomenon. A possible mechanism for this is capillary endothelial damage secondary to the presence of formed blood cells or their products of hemolysis. Perfusion washout may improve ischemic tolerance by preventing this blood cell-induced endothelial damage and by the prevention of sludge and thrombus. Whether any of the metabolic components of the perfusate actively enhance ischemic tolerance cannot be definitively stated.

Experience with epigastric free flap transfer in the rat: technique and results.

We have described the advantages and disadvantages of using the rat epigastric free flap as a means of studying transplantation phenomena. The study comprises 20 epigastric free flap autografts in rats. After 1 1/2 years of working on the model, we achieved a 75% success rate in the last 20 consecutive procedures. From our experience with this model, we feel that the rat epigastric flap has a place in the study of transplantation phenomena in the experimental laboratory. In addition, we feel that this is an excellent technical exercise for maintaining proficiency in performing microvascular anastomoses.

Interstitial fluid pressure as a circulatory monitor in skin flaps

Intradermal interstitial fluid pressure (IFP) in the rat epigastric flap has been measured under varying conditions of blood flow. Pressure changes were not as expected. An attempt has been made to explain these anomalous results using radiolabelled isotopes.