The role of the venous system in the abdominal flap of the rat

Effect of short-term ischemia on microcirculation and wound healing of adipocutaneous flaps in the rat

PURPOSE

Composite flaps used in reconstructive surgery may intra- and postoperatively suffer from hypoperfusion and/or ischemia-reperfusion influencing wound healing. We aimed to follow-up the effect of ischemia on adipocutaneous flaps' wound healing and microcirculation.

METHODS

In anesthetized rats groin flaps were formed bilaterally. In Control group the flaps were repositioned and sutured back. In Ischemia-Reperfusion (I/R) group before repositioning and suturing the flap pedicles were clamped for 60 minutes. Laser Doppler (LD) fluxmetry and temperature probes were applied on the cranial, central and caudal flap regions before/after preparation and ischemia, re-suturing, and on the 1st-3rd-5th-7th-14th postoperative days, before the final examinations and biopsies for histology.

RESULTS

Flaps' skin temperature quickly recovered after repositioning. LD values were lower in the I/R group, reaching a significant level by the 3rd postoperative day, and remained lowered till the 14th day. The magnitude of alterations differed in the flap regions. Histologically normal wound healing process was seen, except for some I/R flaps, where hypertrophized mammary glands were found.

CONCLUSIONS

Short-term ischemia could influence flap microcirculation and wound healing, and may result in hypertrophized mammary glands. Laser Doppler could be used to evaluate intra- and postoperative microcirculatory changes and may have significance in predicting complications.

Unconventional Perfusion Flaps in the Experimental Setting: A Systematic Review and Meta-Analysis

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Background:

Unconventional perfusion flaps offer multiple potential advantages compared with traditional flaps. Although there are numerous experimental articles on unconventional perfusion flaps, the multiple animal species involved, the myriad vascular constructions used, and the frequently conflicting data reported make synthesis of this information challenging. The main aim of this study was to perform a systematic review and meta-analysis of the literature on the experimental use of unconventional perfusion flaps, to identify the best experimental models proposed and to estimate their global survival rate.

Methods:

The authors performed a systematic review and meta-analysis of all articles written in English, French, Italian, Spanish, and Portuguese on the experimental use of unconventional perfusion flaps and indexed to PubMed from 1981 until February 1, 2017.

Results:

A total of 68 studies were found, corresponding to 86 optimized experimental models and 1073 unconventional perfusion flaps. The overall unconventional perfusion flap survival rate was 90.8 percent (95 percent CI, 86.9 to 93.6 percent; p < 0.001). The estimated proportion of experimental unconventional perfusion flaps presenting complete survival or nearly complete survival was 74.4 percent (95 percent CI, 62.1 to 83.7 percent; p < 0.001). The most commonly reported animal species in the literature were the rabbit (57.1 percent), the rat (26.4 percent), and the dog (14.3 percent). No significant differences were found in survival rates among these species, or among the diverse vascular patterns used.

Conclusion:

These data do not differ significantly from those reported regarding the use of unconventional perfusion flaps in human medicine, suggesting that rabbit, rat, and canine experimental unconventional perfusion flap models may adequately mimic the clinical application of unconventional perfusion flaps.

Blood Supply to the Integument of the Abdomen of the Rat: A Surgical Perspective

BACKGROUND

Many fundamental questions regarding the blood supply to the integument of the rat remain to be clarified, namely the degree of homology between rat and humans. The aim of this work was to characterize in detail the macro and microvascular blood supply to the integument covering the ventrolateral aspect of the abdominal wall of the rat.

METHODS

Two hundred five Wistar male rats weighing 250-350 g were used. They were submitted to gross anatomical dissection after intravascular colored latex injection (n = 30); conversion in modified Spalteholz cleared specimens (n=10); intravascular injection of a Perspex solution, and then corroded, in order to produce vascular corrosion casts of the vessels in the region (n = 5); histological studies (n = 20); scanning electron microscopy of vascular corrosion casts (n = 10); surgical dissection of the superficial caudal epigastric vessels (n = 100); and to thermographic evaluation (n = 30).

RESULTS

The ventrolateral abdominal wall presented a dominant superficial vascular system, which was composed mainly of branches from the superficial caudal epigastric artery and vein in the caudal half. The cranial half still received significant arterial contributions from the lateral thoracic artery in all cases and from large perforators coming from the intercostal arteries and from the deep cranial epigastric artery.

CONCLUSIONS

These data show that rats and humans present a great deal of homology regarding the blood supply to the ventrolateral aspect of the abdominal integument. However, there are also significant differences that must be taken into consideration when performing and interpreting experimental procedures in rats.

The complicated role of venous drainage on the survival of arterialized venous flaps

The arterialized venous flap (AVF) has been gradually popularized in clinical settings; however, its survival is still inconsistent and the role of venous drainage remains elusive. In this study, we aimed to investigate the role of venous drainage on the flap survival of arterialized venous flaps. An arterialized venous flap was outlined symmetrically in the rabbit abdomen. The arterial perfusion flap with a unilateral vascular pedicle was taken as the control group and three other experimental groups (I, II and III) were designed based on the number of drainage veins (n = 1, 2 and 3 in the three groups, respectively). Compared with the control group, significant venous congestion was noted in all the experimental groups and the most severe one was seen in group I; while no statistical difference was observed between groups II and III. Similar results regarding blood perfusion state, epidermal metabolite levels and flap survival status were obtained among the three groups. These findings suggested that venous drainage is vital in the survival of the flap, but unlike in the arterial perfusion flaps, the problem of venous congestion can only be partially solved by increasing the number of draining veins. Further studies are warranted to gain insight into this complicated issue.

Optimization of an Arterialized Venous Fasciocutaneous Flap in the Abdomen of the Rat

BACKGROUND

Although numerous experimental models of arterialized venous flaps (AVFs) have been proposed, no single model has gained widespread acceptance. The main aim of this work was to evaluate the survival area of AVFs produced with different vascular constructs in the abdomen of the rat.

METHODS

Fifty-three male rats were divided into 4 groups. In group I (n = 12), a 5-cm-long and 3-cm-wide conventional epigastric flap was raised on the left side of the abdomen. This flap was pedicled on the superficial caudal epigastric vessels caudally and on the lateral thoracic vein cranially. In groups II, III, and IV, a similar flap was raised, but the superficial epigastric artery was ligated. In these groups, AVFs were created using the following arterial venous anastomosis at the caudal end of the flap: group II (n = 13) a 1-mm-long side-to-side anastomosis was performed between the femoral artery and vein laterally to the ending of the superficial caudal epigastric vein. In group III (n = 14), in addition to the procedure described for group II, the femoral vein was ligated medially. Finally, in group IV (n = 14), the superficial caudal epigastric vein was cut from the femoral vein with a 1-mm-long ellipse of adjacent tissue, and an end-to-side arterial venous anastomosis was established between it and the femoral artery.

RESULTS

Seven days postoperatively, the percentage of flap survival was 98.89 ± 1.69, 68.84 ± 7.36, 63.84 ± 10.38, 76.86 ± 13.67 in groups I-IV, respectively.

CONCLUSION

An optimized AVF can be produced using the vascular architecture described for group IV.

Effects of Venous Superdrainage and Arterial Supercharging on Dorsal Perforator Flap in a Rat Model

Objective

To comparatively assess the effects of venous superdrainage and arterial supercharging on dorsal perforator flap survival.

Materials and Methods

Sixty male Sprague-Dawley rats (450–550g) were randomly divided into three groups (n = 20), including control group (Control) and experimental groups A (venous superdrainage, Exp. A) and B (arterial supercharging, Exp. B). At postoperative day 7, survival areas of the flaps were evaluated and all animals underwent angiography. Laser Doppler was used to evaluate flap perfusion from 0h to 7days after surgery. Histology with hematoxylin and eosin staining was used to count microvessels. Tissue of “Choke vessels”was excised for quantification of hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) by western blot assay at 6h and 7days after surgery.

Results

In the Exp. A group, almost all flaps survived (98.2±1.6%); in the Exp. B and control group, survival areas accounted for 78.8±8.5% and 60.3±7.8%, respectively (P <0.001). In addition, Exp. A animals showed improved anastomosis of choke vessels 2 compared with the Exp. B and Control groups. Furthermore, flap blood flow and partial pressure of oxygen in the Exp. A group were significantly higher compared with values obtained for the Exp. B and Control groups, from 6 hours to 7 days after surgery. More microvessels were found in the Exp. A group (11.65±1.33) than in Exp. B (9.25±0.34) and control (7.25±0.91) animals on POD 7. The relative expression level of HIF-1α and VEGF were significant at 6h and 7days after surgery.

Conclusions

Venous superdrainage in rat dorsal perforator flap is more effective than arterial supercharging in promoting flap survival, and could effectively alter hemodynamics in the microcirculation and stimulate blood vessel formation.

The position of 'shunt restriction' along an arterialized vein affects venous congestion and flap perfusion of an arterialized venous flap

Restriction of arteriovenous (AV) shunting has been shown to enhance peripheral perfusion and also reduce venous congestion of an arterialized venous flap. Thus, this study is designed to investigate the effect of 'shunt-restriction' location on venous congestion and flap perfusion in a 'shunt-restricted' arterialized venous flap (AVF).

METHODS

Abdominal flaps based on the thoracoepigastric vessels of Sprague-Dawley rats were raised. The inferior epigastric vein was repaired to the femoral artery in order to create an AVF. The superior epigastric vein was preserved for drainage. Microcirculation and laser Doppler flowmetry results were compared between AVFs with 'shunt restriction' at a proximal third (SR-proximal) distance and 'shunt restriction' at a distal third (SR-distal) distance.

RESULTS

Bidirectional sluggish flow was detected at the proximal part of venous flaps in both groups. Unidirectional normal flow was observed in more capillaries of the distal flaps in the SR-proximal group. In the middle of the flaps, blood flow was sluggish and intermittent in the veins and was absent in most capillaries of the SR-distal group. The flow was prompt and unidirectional in more capillaries of the SR-proximal group. Using laser Doppler flowmetry, the average perfusion of the whole SR-proximal flaps was found to be higher than that of SR-distal flaps (p = 0.017). The average flux at the middle and distal portions of the SR-proximal group was significantly higher than those of the SR-distal group (p = 0.049).

CONCLUSION

'Shunt restriction' at the proximal third of the AV shunt resulted in enhanced perfusion and reduced venous congestion in an AVF.

The venous anatomy of the abdominal wall for Deep Inferior Epigastric Artery (DIEP) flaps in breast reconstruction

BACKGROUND

Despite improving outcomes, venous problems in the harvest of deep inferior epigastric artery perforator (DIEP) flaps remain the more common vascular complications. However, it is apparent that the venous anatomy of the anterior abdominal wall has not been described to the same extent as the arterial anatomy. Cadaveric dissection studies of venous anatomy frequently lack the detail of their arterial counterparts. Venous valves complicate retrograde injection, resulting in poor quality studies with limited anatomical information.

METHODS

The current manuscript comprises a review of the literature, highlighting key features of the anatomy of the venous drainage of the abdominal wall integument, with particular pertinence to DIEP flaps. Both cadaveric and clinical studies are included in this review. Our own cadaveric and in-vivo studies were undertaken and included in detail in this manuscript, with the cadaveric component utilizing direct catheter venography and the in-vivo studies were undertaken using preoperative computed tomographic angiography (CTA), mapping in-vivo venous flow.

RESULTS

Several key features of the venous anatomy of the abdominal wall render it different to other regions, and are of particular importance to DIEP flap transfer.

CONCLUSIONS

The cause of venous compromise is multi-factorial, with perforator diameter, midline crossover, and deep-superficial venous communications all important. Venous cadaveric studies as well as clinical CTA preoperatively can identify these anomalies.

The importance of the superficial venous anatomy of the abdominal wall in planning a superficial inferior epigastric artery (SIEA) flap: case report and clinical study

The importance of the venous drainage of the anterior abdominal wall to free tissue transfer in deep inferior epigastric artery perforator flap surgery has been highlighted in several recent publications in this journal, however the same attention has not been given to superficial inferior epigastric artery (SIEA) flaps, in which the flap necessarily relies on the superficial venous drainage. We describe a unique case, in which the presence of two superficial inferior epigastric veins (SIEVs) draining into separate venous trunks was identified. The use of only one trunk led to a well-demarcated zone of venous congestion. A clinical study was also conducted, assessing 200 hemiabdominal walls with preoperative computed tomographic angiography imaging. The presence of more than a single major SIEV trunk was present in 80 hemiabdominal walls (40% of overall sides). There was considerable variability in the source of drainage of the SIEV, draining variably into the deep inferior epigastric vein, the great saphenous vein, the saphenous bulb, a common trunk with the superficial circumflex iliac vein or a common trunk with a second branch of the SIEV. These findings highlight the considerable variation in the number of SIEV trunks as well as their source of regional drainage, and show the importance of consideration of such variation.

Effect of Venous Superdrainage on a Four-Territory Skin Flap Survival in Rats

BACKGROUND

In a previous report, the authors demonstrated that distal arterial supercharging is more effective at increasing flap survival. There is no doubt of the benefit of arterial augmentation in flap surgery, but the effect of venous superdrainage is still controversial. The purpose of this study was to investigate how venous augmentation could generate larger flap survival areas with different superdrainage positions in rats.

METHODS

A four-territory skin flap, developed by the authors, was used. Forty rats were divided into four groups, as follows: group 1, flaps based only on the deep circumflex iliac artery and vein; group 2, flaps superdrained with the ipsilateral superficial inferior epigastric vein; group 3, flaps superdrained with the contralateral superficial inferior epigastric vein; and group 4, flaps superdrained with the contralateral deep circumflex iliac vein. On the fourth postoperative day, the flaps were assessed by measurements of necrosis and survival areas. Vascular changes produced by venous augmentation were evaluated angiographically.

RESULTS

Compared with group 1 (mean flap survival, 37.8 +/- 5.0 percent), the flap survival areas were significantly greater in the superdrainage flap groups (group 2, 57.4 +/- 6.5 percent, p < 0.001; group 3, 72.4 +/- 21.3 percent, p < 0.001, and group 4, 89.2 +/- 18.8 percent; p < 0.001). Angiographic assessment of the flaps revealed dilatation of the choke vein between the territories and reorientation of dilated veins along the long axes of the flaps.

CONCLUSIONS

This study demonstrates that venous augmentation is also effective for increasing flap survival, and the distal procedure is more effective than the proximal procedure in arterial supercharging.

Efficacy of Venous Supercharging of the Deep Inferior Epigastric Perforator Flap in a Rat Model

BACKGROUND

An insidious risk with the use of muscle perforator flaps is the possibility of venous outflow compromise. Congestion in deep inferior epigastric perforator (DIEP) flaps in particular is not infrequent. On an empiric basis, their salvage has been accomplished by augmenting venous drainage through alternative outflow tracts. The validity of this clinical maneuver can now best be tested in a rat DIEP flap model.

METHODS

The rat DIEP flap is a modification of the rat ventral abdomen flap. Flap perfusion can be based on a single rectus abdominis musculocutaneous perforator. No muscle is included with the flap. Three groups of five male Sprague-Dawley rats each were used. The conventional DIEP flap group had only a solitary perforator artery and venae comitantes and served as the control. The contralateral superficial inferior epigastric vein was included with the flap in the other two groups as a distinctly separate venous outflow tract. The latter two groups differed in that the perforator venae comitantes were either retained or deleted.

RESULTS

Mean flap survival in the control DIEP flap group was 80.8 +/- 16.3 percent. Retention of the contralateral superficial inferior epigastric vein resulted in a statistically significant enhancement in flap viability (p < 0.027) whether the perforator venae comitantes were left intact (99.8 +/- 0.4 percent) or had been intentionally ablated (99.6 +/- 0.5 percent).

CONCLUSIONS

Venous supercharging of the rat DIEP flap ensures greater flap survival. As a corollary, this supports the efficacy of prior anecdotal experiences in which an alternative venous outflow tract, preferably from the superficial system, had been used to overcome venous congestion. It is advisable for any muscle perforator flap to always try to retain a second outflow source to allow the potential for venous supercharging, if later indicated.

Venous “Supercharging” Augments Survival of the Delayed Rat TRAM Flap

Adequate delay of a pedicled transverse rectus abdominis musculocutaneous (TRAM) flap might not necessarily require interruption of the venous system. The retained ipsilateral deep vein of the dominant pedicle could then be used as a secondary outflow source for potential salvage of a congested flap. A venous "supercharged" rat TRAM flap model has been designed to evaluate the efficacy of this maneuver. Seventy-two female Sprague-Dawley rats (CD) were equally divided into two major groups, differing only in whether a delay by division of the dominant cranial epigastric artery had first been performed. An inferior-based TRAM flap (nondominant) was raised for each rat, with three subsets of 12 rats in each group, ie, with the cranial epigastric vein subsequently divided (group control), retained (supercharged), or retained but the inferior pedicle divided (venous flap). Both supercharged subsets had significantly augmented flap survival when compared with flaps in their group raised without the cranial epigastric vein, whether a delay maneuver had (96 +/- 6% vs 89 +/- 7%; P = 0.012) or not (80 +/- 8% vs 65 +/- 21%; P = 0.034) been performed. Flaps with only a cranial epigastric vein pedicle totally necrosed, implying that the observed enhancement in flap viability was not the result of transformation into a venous flap, but perhaps as a crossover flap where an adjacent venosome was captured. Venous supercharging can be accomplished by inclusion of the ipsilateral dominant deep vein, and should be a consideration in the clinical planning of delay maneuvers and for treatment of the compromised TRAM flap.

The relative importance of the deep and superficial vascular systems for delay of the transverse rectus abdominis musculocutaneous flap as demonstrated in a rat model

The use of some form of delay maneuver for "high-risk" patients before transfer of the superior pedicled lower transverse rectus abdominis musculocutaneous (TRAM) flap for breast reconstruction has augmented the rate of success in both the experimental and clinical arenas. A common method of vascular delay has been the bilateral division of both the superficial inferior epigastric and deep inferior epigastric vessels. Whether all of these must be divided to adequately effect the delay is unknown. For that matter, the relative importance of the superficial versus the deep vascular systems is unclear. To investigate this uncertainty, a delay was attempted in 61 Sprague-Dawley rats by division of either the superficial inferior epigastric or deep cranial epigastric vessels (the latter is the homologue to the human deep inferior epigastric) in unilateral or bilateral fashion. Division of the contralateral superficial inferior epigastric vessel resulted in significantly greater TRAM flap survival than either ipsilateral or bilateral superficial inferior epigastric vessel division (p = 0.0034 or p = 0.0093, respectively). Division of the ipsilateral or bilateral deep cranial epigastric vessel resulted in significantly greater flap survival than just contralateral deep cranial epigastric vessel division (p = 0.0034 or p = 0.006, respectively). No significant difference was observed between the group having contralateral superficial inferior epigastric or groups with ipsilateral deep cranial epigastric division, implying that either alone would be efficacious to achieve the desired delay effect. This would allow the other vascular system to be retained intact for later potential salvage maneuvers as needed.

Do superficial epigastric veins of rats have valves?

The rat is a good model for experimental studies on the haemodynamic patterns of free-flap transfer but models involving the superficial epigastric vein have not been supported by the demonstration of the anatomical presence or absence of valves inside it. We performed a morphological study to assess whether or not valves are present inside the superficial epigastric vein of the rat. Segments of superficial epigastric veins were explanted from fifteen Sprague-Dawley rats. The lumen was studied with scanning electron microscopy after longitudinal or transverse incision of the venous walls. No valves were detected and we saw no evidence of their accidental removal. As most human veins do have valves, the clinical implications of haemodynamic data on reverse-flow island flaps obtained in rats must be considered very carefully.

Experimental model for transplantation of a modified free myocutaneous gracilis flap to an irradiated neck region in rats

In 102 Wistar rats (male, weight 300-500 g), a modified free myocutaneous gracilis flap was obtained from the groin and transplanted to the neck. To create a pre-irradiated transplant bed, a local area of the neck was irradiated preoperatively with 30 Gy (fractionation: 3 x 10 Gy) in 30 animals, and with 50 Gy (fractionation: 5 x 10 Gy) in a further 30 animals. The interval between preoperative irradiation and transplantation was 4 weeks. Forty-two animals received no such preoperative radiation. The evaluation of healing and the success of the transplanted flap was based on a clinical assessment, carried out on postoperative days 1 7. Testing for significant differences was done nonparametrically using the Kruskal-Wallis test. The survival rate in the nonirradiated animals was 86%. In contrast, the healing of the free flaps in the pre-irradiated transplant bed was significantly lower (P=0.003) 76%, after irradiation with 30 Gy and 50% after 50 Gy. The significant difference (P=0.020) in survival rates after irradiation with 30 and 50 Gy was evidence for the dependence of successful healing on the preoperative radiation dose. Transplantation of the free myocutaneous gracilis flap to a previously irradiated transplant bed in the region of the neck is a suitable model for investigating the healing of free transplants to irradiated tissue. The success rate observed in non-irradiated transplant beds is comparable to that seen with other flap models in rats.