The rat rectus abdominis myocutaneous flap: a true myocutaneous flap model

Standardized Pre-clinical Surgical Animal Model Protocol to Investigate the Cellular and Molecular Mechanisms of Ischemic Flap Healing

BACKGROUND

Some of the most complex surgical interventions to treat trauma and cancer include the use of locoregional pedicled and free autologous tissue transfer flaps. While the techniques used for these reconstructive surgery procedures have improved over time, flap complications and even failure remain a significant clinical challenge. Animal models are useful in studying the pathophysiology of ischemic flaps, but when repeatability is a primary focus of a study, conventional in-vivo designs, where one randomized subset of animals serves as a treatment group while a second subset serves as a control, are at a disadvantage instigated by greater subject-to-subject variability. Our goal was to provide a step-by-step methodological protocol for creating an alternative standardized, more economical, and transferable pre-clinical animal research model of excisional full-thickness wound healing following a simulated autologous tissue transfer which includes the primary ischemia, reperfusion, and secondary ischemia events with the latter mimicking flap salvage procedure.

RESULTS

Unlike in the most frequently used classical unilateral McFarlane's caudally based dorsal random pattern skin flap model, in the herein described bilateral epigastric fasciocutaneous advancement flap (BEFAF) model, one flap heals under normal and a contralateral flap-under perturbed conditions or both flaps heal under conditions that vary by one within-subjects factor. We discuss the advantages and limitations of the proposed experimental approach and, as a part of model validation, provide the examples of its use in laboratory rat (Rattus norvegicus) axial pattern flap healing studies.

CONCLUSIONS

This technically challenging but feasible reconstructive surgery model eliminates inter-subject variability, while concomitantly minimizing the number of animals needed to achieve adequate statistical power. BEFAFs may be used to investigate the spatiotemporal cellular and molecular responses to complex tissue injury, interventions simulating clinically relevant flap complications (e.g., vascular thrombosis) as well as prophylactic, therapeutic or surgical treatment (e.g., flap delay) strategies in the presence or absence of confounding risk factors (e.g., substance abuse, irradiation, diabetes) or favorable wound-healing promoting activities (e.g., exercise). Detailed visual instructions in BEFAF protocol may serve as an aid for teaching medical or academic researchers basic vascular microsurgery techniques that focus on precision, tremor management and magnification.

Effects of açaí and cilostazol on skin microcirculation and viability of TRAM flaps in hamsters

BACKGROUND

Tissue necrosis caused by insufficient perfusion is a major complication in flap transfer. This study evaluated whether treatment with cilostazol or hydroalcoholic extract of seeds of Euterpe oleracea Mart. (açaí) protects the transverse rectus abdominis myocutaneous (TRAM) flap against ischemic damage in hamsters.

MATERIALS AND METHODS

Fifty-four hamsters were divided into three oral treatment groups: placebo, açaí, or cilostazol. Caudally based, unipedicled TRAM flaps were raised, sutured back, classified into four vascular zones (I-IV), and evaluated for tissue viability, capillary blood flow (CBF), perfused vessel density (PVD), and microvascular flow index (MFI) by orthogonal polarization spectral imaging at three time points: immediately postoperatively (IPO), 24 h postoperatively (24hPO), and 7 d postoperatively (7POD).

RESULTS

Comparing to placebo, açaí increased PVD at IPO and açaí and cilostazol increased CBF and PVD at 24hPO in zone I; cilostazol increased CBF, PVD, and MFI at IPO, and CBF at 24hPO in zone II; açaí and cilostazol increased CBF at all time points and PVD and MFI at IPO and 24hPO in zone III; cilostazol increased CBF at IPO and 7POD, açaí increased CBF at 7POD, and both increased PVD and MFI at all time points in zone IV; and açaí and cilostazol increased the percentage of viable area in zones III and IV.

CONCLUSIONS

Açaí and cilostazol treatments had a protective effect against ischemic damage to TRAM flaps in hamsters, improving microvascular blood flow and increasing the survival of flap zones contralateral to the vascular pedicle (zones III and IV).

Glucose level evaluation in monopedicled rectus abdominis myocutaneous flap after venous occlusion: experimental study in rats

OBJECTIVE

to validate an experimental model for the measurement of glycemic levels in surgical flaps with the use of common glucometers, and to analyze the diagnostic criteria for hypoperfusion of such flaps.

METHODS

we performed vertical myocutaneous rectus abdominis flaps with upper pedicles bilaterally in 20 male Wistar rats, divided into two groups: with and without venous occlusion of the pedicle. We measured glucose levels in the flaps and in the systemic circulation with standard glucometers. We tested the accuracy of alternative diagnostic criteria for the detection of hypoperfusion.

RESULTS

from 15 minutes of venous occlusion on, there was a significant reduction in glucose levels measured in the congested flap (p<0.001). Using a minimum difference of 20mg/dl in the glycemic levels between the flap and systemic blood, 30 minutes after occlusion, as a diagnostic criterion, the sensitivity was 100% (95% CI 83.99-100%) and specificity of 90% (95% CI 69.90-97.21%) for the diagnosis of flap congestion.

CONCLUSION

It is possible to measure glucose levels in vertical myocutaneous rectus abdominis flaps of Wistar rats, perfused or congested, using a common glucometer. The diagnostic criteria that compare the glucose levels in the flaps with the systemic ones were more accurate in the evaluation of tissue perfusion.

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.

A Model of Free Tissue Transfer: The Rat Epigastric Free Flap

Free tissue transfer has been increasingly used in clinical practice since the 1970s, allowing reconstruction of complex and otherwise untreatable defects resulting from tumor extirpation, trauma, infections, malformations or burns. Free flaps are particularly useful for reconstructing highly complex anatomical regions, like those of the head and neck, the hand, the foot and the perineum. Moreover, basic and translational research in the area of free tissue transfer is of great clinical potential. Notwithstanding, surgical trainees and researchers are frequently deterred from using microsurgical models of tissue transfer, due to lack of information regarding the technical aspects involved in the operative procedures. The aim of this paper is to present the steps required to transfer a fasciocutaneous epigastric free flap to the neck in the rat.

This flap is based on the superficial epigastric artery and vein, which originates from and drain into the femoral artery and vein, respectively. On average the caliber of the superficial epigastric vein is 0.6 to 0.8 mm, contrasting with the 0.3 to 0.5 mm of the superficial epigastric artery. Histologically, the flap is a composite block of tissues, containing skin (epidermis and dermis), a layer of fat tissue (panniculus adiposus), a layer of striated muscle (panniculus carnosus), and a layer of loose areolar tissue.

Succinctly, the epigastric flap is raised on its pedicle vessels that are then anastomosed to the external jugular vein and to the carotid artery on the ventral surface of the rat's neck. According to our experience, this model guarantees the complete survival of approximately 70 to 80% of epigastric flaps transferred to the neck region. The flap can be evaluated whenever needed by visual inspection. Hence, the authors believe this is a good experimental model for microsurgical research and training.

The protective effect of cilostazol on transverse rectus abdominis myocutaneous flap in rats

OBJECTIVE

Transverse Rectus Abdominis Myocutaneous (TRAM) flap is commonly used in breast reconstruction. The aim of this study is to demonstrate the effects of cilostazol on TRAM flap viability in a rat TRAM model.

METHODS

Twenty-four Wistar rats were used. They were divided into four groups. Rats in Group 1 were applied TRAM flap. In Group 2, cilostazol 30 mg/kg was administered to rats via oral gavage 3 hours before the flap surgery. After the flap surgery, cilostazol 30 mg/kg was administered via oral gavage twice a day for 7 days. In Group 3 before the flap surgery, cilostazol 30 mg/kg was administered via oral gavage twice a day for 7 days, and treatment continued for 7 more days after the flap surgery. In Group 4 before the flap surgery, cilostazol 30 mg/kg was administered via oral gavage twice a day for 7 days and treatment was discontinued after the flap surgery.

RESULT

The mean necrosis rate in Group 1 was 41.69%, in Group 2 it was 27.0%, in Group 3 it was 6.66%, and in Group 4 it was 11.2%. The necrosis rate in Group 1 was found to be statistically significantly higher than other groups (p < .01), the necrosis rate in Group 2 was found to be statistically significant higher than Groups 3 and 4 (p < .01), and the necrosis rate in Group 4 was found to be statistically significant higher than Group 3 (p < .01).

CONCLUSION

Cilostazol treatment seemed to increase the viability of TRAM flap, especially when administered as adjuvant therapy.

In situ transverse rectus abdominis myocutaneous flap: a rat model of myocutaneous ischemia reperfusion injury

Free tissue transfer is the gold standard of reconstructive surgery to repair complex defects not amenable to local options or those requiring composite tissue. Ischemia reperfusion injury (IRI) is a known cause of partial free flap failure and has no effective treatment. Establishing a laboratory model of this injury can prove costly both financially as larger mammals are conventionally used and in the expertise required by the technical difficulty of these procedures typically requires employing an experienced microsurgeon. This publication and video demonstrate the effective use of a model of IRI in rats which does not require microsurgical expertise. This procedure is an in situ model of a transverse abdominis myocutaneous (TRAM) flap where atraumatic clamps are utilized to reproduce the ischemia-reperfusion injury associated with this surgery. A laser Doppler Imaging (LDI) scanner is employed to assess flap perfusion and the image processing software, Image J to assess percentage area skin survival as a primary outcome measure of injury.

Comparisons of the postoperative rectus abdominis muscle thickness and the biomechanical properties of donor sites among different subtypes of muscle-sparing transverse rectus abdominis myocutaneous flaps (MS0, MS1, MS2, MS3): a rat model

BACKGROUND

The primary presumed advantages of the deep inferior epigastric perforator flap over the other muscle-sparing (MS) transverse rectus abdominis myocutaneous flaps are the improved functional rectus abdominis muscle outcomes and decreased abdominal contour morbidities. The purpose of this study was to verify this viewpoint objectively and quantitatively using an animal model.

METHODS

Six rats were used in the pilot study and 40 rats were equally divided into a control group and 4 experimental groups (MS0, MS1, MS2, and MS3) according to the amount of rectus abdominis muscles harvested. At 3 and 6 weeks, 4 rats in each group were killed, then, the percentage of residual rectus abdominis muscle thickness compared with the control side and the ultimate load at failure of the abdominal wall were recorded and compared.

RESULTS

All of the flaps survived completely without complications. Regarding the percentage of residual rectus abdominis muscle thickness compared with the control side, the results suggested MS3 > MS2 ≈ MS1 > MS0; concerning the ultimate load at failure of the abdominal wall, the results showed MS3 ≈ MS2 > MS1 > MS0. (≈: P > 0.05; >: P < 0.05).

CONCLUSIONS

According to the findings of this study, we advocate the use of the deep inferior epigastric perforator flap when possible, and the MS2-transverse rectus abdominis myocutaneous flap can serve as a backup when the perforator anatomy does not meet the flap safety criteria for preservation of rectus abdominis muscle function.

Effect of Hydrostatic Dilation on Flap Viability of the Transverse Rectus Abdominis Musculocutaneous Flap Model in Rats

BACKGROUND

The technique of intraoperative vessel hydrostatic dilation is sometimes used to facilitate microvascular anastomosis and prevent vasospasm. Currently, delay procedures remain a reliable method of maximizing flap survival. The authors aimed to increase rat transverse rectus abdominis musculocutaneous (TRAM) flap viability by imitating the physical effect of a surgical delay procedure with hydrostatic dilation.

METHODS

Forty-five male Sprague-Dawley rats were randomly assigned to one of three TRAM flap groups (15 rats in each group): the control group, the delay group, and the hydrostatic dilation group. The surgical delay procedure was performed by division of right-sided cranial epigastric vessels and contralateral superficial inferior epigastric vessels. While elevating the flap, hydrostatic dilation was performed to the cranial epigastric artery and vein with a mean pressure of 250 mm Hg. The groups were compared by means of microangiography and survival ratio of TRAM flaps and mean artery lumen area, mean vein lumen area, and mean artery wall area of the flap pedicle 48 hours after elevation.

RESULTS

There was a significant difference between the control and hydrostatic dilation groups in favor of surface area viability and angiographic assessment (p < 0.01). Surgical delay has traditionally been accepted as the most reliable method of enhancing flap viability. No significant difference was revealed between the surgical delay and hydrostatic dilation groups (p > 0.05). In the hydrostatic dilation group, compared with the control group, an increase in vein diameter, a thinning of the artery wall, and an increase in lumen diameter were observed.

CONCLUSIONS

The physical effect of blood flow is achieved acutely with hydrostatic dilation. This simple, dependable, one-stage hydrostatic dilation procedure can be used in clinical applications.

Dichloroacetate Reduces Tissue Necrosis in a Rat Transverse Rectus Abdominis Musculocutaneous Flap Model

OBJECTIVE

Ischemia-related complications may occur during postmastectomy transverse rectus abdominis musculocutaneous (TRAM) flap reconstruction. The aim of our study was to investigate whether necrosis of susceptible flap regions could be reduced by dichloroacetate (DCA)-induced stimulation of oxidative metabolism in hypoxic tissue.

METHODS

The study was a randomized control trial using male Sprague-Dawley rats. A pedicled TRAM flap based upon the right inferior epigastric artery was elevated and reapproximated. Animals were randomly assigned to 1 of 5 treatment groups (n = 6). Group I received no DCA; groups II through V were administered 75 mg/kg DCA orally 24 hours preoperative; in addition, groups II through IV received 75 mg/kg/d DCA orally postoperative for 4 days; group III also received 75 mg/kg DCA (IP) intraoperatively; groups IV and V were given 15 mg/kg/d DCA orally for 6 days before the 24-hour preoperative treatment. Four days postsurgery, skin paddles were photographed and assessed for viability. Underlying TRAM muscle was biopsied for histologic analysis. Blood lactate levels were measured at pre- and postoperative time points. The mean percentages of viable skin paddle were as follows: 32.0%+/- 4.0% (group I), 68.1% +/- 6.2% (group II), 84.3% +/- 5.9% (group III), 92.8% +/- 2.0% (group IV), 82.6% +/- 5.8% (group V).

RESULTS

Statistically significant differences were found in all experimental (DCA) groups relative to the controls (P < 0.01). Group IV (6-day DCA preconditioning, plus 24-hour preoperative and 4-day postoperative treatment) displayed the greatest improvement in flap viability, significantly better than other DCA groups (P < 0.01). Group IV also had significantly lower serum lactate levels than controls (P < 0.05). Histologic examination of muscle biopsies revealed reductions in inflammation and necrosis correlating with DCA treatment and skin paddle survival.

CONCLUSIONS

This study indicates that DCA may provide a useful pharmacologic tool for reducing ischemia-related necrosis in TRAM flaps.

Is it Possible to Increase the Survival of the Transverse Rectus Abdominis Musculocutaneous Flap following previous Abdominoplasty Using a Delay Procedure? An Experimental Study in the Rat

BACKGROUND

Although, because of the disruption of perforators, abdominoplasty has been suggested as a major contraindication for patients undergoing autologous breast reconstruction with the transverse rectus abdominis musculocutaneous (TRAM) flap, many researchers encourage the search for a means of improving the survival of the skin paddle of the flap in patients who have undergone previous abdominoplasty. In this study, the effect of the surgical delay phenomenon on the survival of the TRAM flap following abdominoplasty was investigated.

METHODS

Thirty adult Wistar rats were used: the control group (n = 6), the short-term group (n = 12), and the long-term group (n = 12). In the control group, a standard superior pedicled TRAM flap was harvested with no abdominoplasty procedure, and the flap was replaced in situ. In all other animals, an abdominoplasty procedure was performed initially. The short-term and long-term groups were divided into two subgroups: the abdominoplasty plus TRAM-only subgroup (n = 6), and the abdominoplasty plus delay plus TRAM subgroup (n = 6). In the short-term group, the experiment was performed 1 month after abdominoplasty, whereas the same surgical procedures were applied 6 months after abdominoplasty in the long-term group.

RESULTS

The short-term abdominoplasty plus TRAM subgroup, the long-term abdominoplasty plus TRAM subgroup, the short-term abdominoplasty plus delay plus TRAM subgroup, the long-term abdominoplasty plus delay plus TRAM subgroup, and the conventional superior pedicled TRAM flap group showed 2.33 +/- 3.01 percent, 13.33 +/- 8.76 percent, 24.17 +/- 13.57 percent, 60 +/- 8.94 percent, and 70.83 +/- 9.70 percent survival rates for the skin paddle, respectively.

CONCLUSION

The data demonstrate that surgical delay after long-term abdominoplasty can enhance the survival rate of the skin paddle of the TRAM flap.

The Effect of Hyperbaric Oxygen on Ischemia–Reperfusion Injury

The effect of hyperbaric oxygen is known to increase survival of ischemic tissue but its mechanism is not fully understood. The purpose of this study was to evaluate the effect of hyperbaric oxygen on a rat musculocutaneous flap versus ischemia-reperfusion injury, focusing on the mechanism involving the expression of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) of endothelial cells and CD18 of neutrophils. A transverse rectus abdominis musculocutaneous (TRAM) flap (6 x 5 cm) supplied by a single superior epigastric vascular pedicle was elevated in 100 Sprague-Dawley rats. The rats were divided into 4 groups: group 0, sham (n = 10); group I, 4 hours of ischemia followed by reperfusion (n = 30); group II, 4 hours of ischemia and hyperbaric oxygen (100% oxygen, 2.5 atm absolute, during the last 90 minutes of ischemia before reperfusion) followed by reperfusion (n = 30); and group III, 4 hours of ischemia followed by reperfusion and hyperbaric oxygen (100% oxygen, 2.5 atm absolute, after reperfusion for 90 minutes; n = 30). The study consisted of gross examination for flap survival, histology, immunohistochemical staining, myeloperoxidase assay, flow cytometric study of CD18, and Northern blot analysis on ICAM-1 messenger ribonucleic acid expression. Gross measurement of the flap showed increased survival in groups II and III compared with group I (P < 0.05). The leukocytes adherent to the endothelium were counted at 24 hours and on day 5. Group I leukocytes were significantly increased compared with groups II and III (P < 0.05). The myeloperoxidase assay of TRAM flaps at 24 hours revealed a significant increase in group I compared with groups II and III (P < 0.05). The expression of CD18 was similar between groups I, II, and III. Immunohistochemical staining for ICAM-1 and Northern blot analysis on ICAM-1 messenger ribonucleic acid showed decreased expression in groups II and III compared with group I. Throughout the analysis, groups II and III did not show any significant differences. These results suggests that hyperbaric oxygen reduces the accumulation of leukocytes in the TRAM flap, but not enough to prevent adhesion of neutrophils on endothelial cells; ischemia-reperfusion injury increases the expression of CD18 and ICAM-1 and causes increased adhesion of leukocytes on the endothelium; hyperbaric oxygen does not alter the expression of CD18 but decreases the expression of ICAM-1; and the point of application for hyperbaric oxygen, whether applied before or after reperfusion, did not show any differences in outcome. In conclusion, the application of hyperbaric oxygen against ischemia-reperfusion injury increases flap survival and the beneficial effect may be explained by a protective mechanism involving downregulation of ICAM-1 on endothelial cells.

A Vertical Midline Scar Is a ‘High-Risk’ Factor for Maximum Survival of the Rat TRAM Flap

The presence of any abdominal scar, in addition to obesity, a smoking history, and prior irradiation are considered the major known "risk factors" for predictable success or failure of the lower transverse rectus abdominis musculocutaneous (TRAM) flap. For many, a vertical midline scar has even been considered to be a relative contraindication. The possibility that the scar instead could effect some form of delay or by neovascularization permit reperfusion across the midline might negate this concern. The validity of this hypothesis was tested in 40 Sprague-Dawley (CD) rats using our standard rat TRAM flap model. Every rat initially had a vertical skin incision made from xiphoid to pubis. At a second stage, either immediately or after a delay of 1 week, 2 weeks, or 6 months, a superior-pedicled (dominant) or inferior-pedicled (nondominant) TRAM flap was raised, with five rats in each subgroup. For the inferior-pedicled group, the percentage of ipsilateral (muscle-pedicle half) flap survival approached 75% and had a trend toward greater survival with each increase in the time of delay, but any difference was not statistically significant (F= 0.653, P = 0.538). In the superior-pedicled group, the ipsilateral half of the flap always survived completely. In both groups, the contralateral or opposite side always underwent complete necrosis regardless of pedicle orientation or time constraints. The midline scar did not enhance even unilateral TRAM flap survival when compared with historic controls, and long-term transmidline reperfusion across the scar did not seem to occur. These findings corroborate the clinical observation that only a unilateral TRAM flap would be reliable in the presence of a vertical midline abdominal scar.

Transverse rectus abdominis musculocutaneous flap (TRAM flap) - experimental model in rats

The objective of this paper was to report the use of an experimental model of the Transverse Rectus Abdominis Musculocutaneous flap (TRAM flap), in rats. Thirty male Wistar rats weighing 180 to 220 g were submitted to the TRAM flap procedure. This article reports on the use of the caudally based, right unipedicled 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.

Formation of independently revascularized bowel segments using the rectus abdominis muscle flap: a rat model for jejunal prefabrication

Reconstruction of the pharyngoesophagus with free jejunal transfer is a major challenge when recipient neck vessels are absent because of previous surgery or irradiation. In such instances, jejunal transfer using a muscle flap as a "vascular carrier" may be a problem-solving alternative. Pretransfer vascularization of the jejunum is achieved by wrapping the muscle flap around the small bowel segment. After a short staging period, the mesenteric pedicle is divided and the bowel segment is transferred up to the neck based on its new blood supply. The objectives of this study were to develop an animal model for prefabricating independently revascularized jejunal segments using the rectus abdominis muscle flap and to determine the minimal time required for independent bowel survival. Twenty-four mature (500-g to 700-g) rats were divided into six experimental groups of four animals each. In each animal, a 1.5-cm segment of proximal jejunum was isolated on two jejunal arteries and wrapped with a superior pedicled rectus abdominis muscle flap. To determine the time of neovascular takeover, the mesenteric pedicles were ligated on postoperative day 2 (group I), day 3 (group II), day 4 (group III), day 5 (group IV), day 6 (group V), and day 7 (group VI). At the time of pedicle ligation, the composite flap was transposed to a new subcutaneous position. Viability of bowel was assessed according to gross appearance and histologic examination 48 hours after transfer. Complete survival of revascularized jejunum in 11 of 12 animals was obtained after pedicle ligation on postoperative day 5 and beyond (p < 0.0001, Fisher's exact test). These bowel segments demonstrated luminal patency, intact pink mucosa, mucus production, and visible peristalsis. Histologic examination showed healthy intestinal epithelium and tissue integration along the serosa-muscle interphase. In contrast, pedicle ligation on day 4 and earlier resulted in varying degrees of bowel necrosis characterized by flattening or ulceration of mucosa (day 4), mucosal sloughing and necrosis of mural musculature (day 3), and complete loss of bowel architecture with lumen obliteration (day 2). These findings suggest that jejunal segments may be independently revascularized with the rectus abdominis muscle flap in the rat model. Complete survival and gross normal bowel function may be obtained without mesenteric perfusion after a minimal time of 5 days.

The effect of prostaglandin E1 versus ischemia-reperfusion injury of musculocutaneous flaps

The purpose of this study was twofold. To evaluate whether prostaglandin El can increase the survival of the flap, and to determine its function against ischemia-reperfusion injury in musculocutaneous flaps. Thirty-five Sprague-Dawley rats weighing 250 to 350 g were analyzed. The transverse rectus abdominis musculocutaneous flap was used in all rats. The rats were divided into three groups: group 1 (N = 15), the control group with 4-hour ischemic injury and intraflap injection of normal saline followed by reperfusion; group 2 (N = 15), prostaglandin E1 intraflap injection of 1 microg immediately after ischemic injury and reperfusion 4 hours later; and group 3 (N = 5), the sham-operated group. Analysis consisted of flap skin survival area measurements, immunohistochemical study using anti-intercellular adhesion molecule (anti-ICAM-1) monoclonal antibody, and histological evaluation including endothelium-sticking leukocytes at 24 hours and 5 days after reperfusion. The group treated with prostaglandin E1 showed immunohistochemical findings with decreased expression of ICAM-1 on the surface of the endothelium, and histology showed significant (p < 0.01) reduction of leukocyte adhesion at 24 hours and 5 days after reperfusion. These two factors were considered to play a role against ischemia-reperfusion injury, and led to improved survival of the flap. These results suggest that prostaglandin E1 may increase flap survival and may have a protective mechanism against ischemia-reperfusion injury by decreasing leukocyte-endothelial cell adhesion through decreased expression of ICAM-1.

In vivo analysis of the microcirculation of osteomyocutaneous flaps using fluorescence microscopy

Previous studies have indicated that freely transferred osteomyocutaneous flaps may fail despite anastomotic patency. While microvascular dysfunction is thought to be one of the major causes for this type of flap failure, little is known of its underlying mechanisms, probably due to the lack of adequate experimental models allowing detailed intravital microcirculatory analysis. Herein we report quantitative analysis of the microcirculation of periosteum, muscle, subcutis and skin by intravital fluorescence microscopy using an osteomyocutaneous free flap model in the hindlimb of rats. The microcirculation of the different tissues was studied after microanastomotic transfer (free flap), and was compared to that after solely elevating the tissue, mimicking a pedicled osteomyocutaneous flap. Transferred flaps, which were exposed to 1 h of ischaemia during the anastomotic procedure, showed a slight but significant decrease (P< 0.05) of functional capillary density in muscle, subcutis and skin when compared with the microcirculation of pedicled flaps, while capillary diameters, red blood cell velocity and blood flow of perfused capillaries remained almost unaffected. The decrease of functional capillary density was associated by a significant (P< 0.05) inflammatory response, as indicated by the increased number of leukocytes adherent to the endothelial lining of postcapillary venules. While the functional capillary density of periosteum was not affected by the free transfer procedure, the inflammatory response was found similar when compared with that observed in muscle and subcutis. Thus, our study indicates that even after a short 1-h ischaemic time period, capillary perfusion failure and leukocyte-endothelial cell interaction are the main events, characterising microvascular dysfunction after free transfer of osteomyocutaneous flaps. Using the model described herein, intravital microscopic analysis of the microcirculation proved an appropriate tool to study the individual microvascular response after free tissue transfer, and may thus be used to evaluate the effectiveness of novel therapeutic regimens which aim at counteracting microcirculatory dysfunction in free osteomyocutaneous flaps.

Effect of hyperbaric oxygen on a rat transverse rectus abdominis myocutaneous flap model

The single-pedicle transverse rectus abdominis myocutaneous (TRAM) flap is frequently associated with partial flap necrosis. Hyperbaric oxygen has previously been shown to increase the survival of skin flaps, although there has been no investigation of possible beneficial effects of hyperbaric oxygen on survival of the TRAM flap. The present study compares the effectiveness of hyperbaric oxygen therapy, normobaric 100% oxygen, a hyperbaric air-equivalent mixture, and no treatment at all (control group), in the prevention of TRAM flap necrosis in a rat model. Forty-eight animals were randomly assigned to one of the four above-mentioned groups. The surviving area of the flap was evaluated 7 days after surgery. The hyperbaric oxygen treatment protocol consisted of five 9-minute sessions breathing 100% oxygen at a pressure of 2.5 atmospheres absolute during the first 48 hours, starting within 1 hour of surgery. The areas of surviving skin paddles ranged from 38.5 percent in the control group to 52.5 percent in the group treated with hyperbaric oxygen. One-way analysis of variance indicated that flap area survival was significantly greater in the hyperbaric oxygen group (F = 2.69, p = 0.05). Tukey's pairwise comparison and the two-sample t test indicated that the group treated with hyperbaric oxygen differed significantly from the control group (Tukey's critical value = 3.8, rejection level = 0.05, t test p = 0.01). Our results suggest that the hyperbaric oxygen treatment protocol used improves survival in the rat TRAM flap. However, the optimal treatment protocol to achieve this objective even in the rat seems to be variable, and further studies are required before extrapolating these data to human applications.

Ischemic preconditioning improves the survival of skin and myocutaneous flaps in a rat model

Inadequate blood supply of pedicle flaps results in partial necrosis, and prolonged ischemia during free-tissue transfer can result in partial or complete flap necrosis. Recent research in the field of cardiovascular surgery has shown that ischemic preconditioning (repeated brief episodes of coronary artery occlusion followed by reperfusion) improves myocardial muscle survival when the heart is subsequently subjected to prolonged ischemia. Preconditioning of skin or myocutaneous flaps as either pedicle or free flap models has never been studied. The goal of this investigation was to measure the effect of ischemic preconditioning on myocutaneous and skin flap survival areas and total necrosis rates after variable periods of global ischemia. In 220 rats, 100 transverse rectus abdominis myocutaneous flaps and 120 dorsal cutaneous flaps were randomized into treatment and control groups. The treatment flaps underwent preconditioning by three cycles of 10 minutes of pedicle clamping followed by 10 minutes of reperfusion for a total preconditioning period of 1 hour. The control flaps were perfused without clamping for 1 hour. Both control and treatment flaps then underwent global ischemia for 0, 2, 4, 6, 10, or 14 hours by pedicle clamping. Flap survival area was measured on the fifth postoperative day. Statistical analysis was performed with analysis of variance, student's t tests, and probit analysis. Preconditioning improved survival areas of pedicle myocutaneous flaps (0-hour group) from 47 +/- 16 percent (mean percent area surviving +/- SD) to 63 +/- 5 percent. This difference was statistically significant (t test, p < 0.04). There was no statistically significant improvement in pedicle skin flap survival. For free flap models (flaps undergoing global ischemia), preconditioning increased the survival areas of skin and myocutaneous flaps (analysis of variance, p < 10(-5)). For the skin flap model, statistical significance of the survival area difference was reached at 6, 10, and 14 hours of ischemia (t test, p < 10(-4)). The magnitude of this effect was higher in the myocutaneous flap model and reached statistical significance at 2, 4, 6, and 10 hours of ischemia (p < 10(-3)). Preconditioned flap survival areas were increased by two to five times that of non-preconditioned flaps at these ischemia times. Preconditioning lowered total necrosis rates at all ischemia times for both flap models. The critical ischemia time when 50 percent of skin flaps became totally necrotic (CIT50) improved from 6.9 to 12.4 hours by preconditioning. Similarly, preconditioning improved the CIT50 of myocutaneous flaps from 3.6 to 9.2 hours. For the first time, statistically significant improvements of partial necrosis areas and total necrosis rates have been demonstrated through intraoperative ischemic preconditioning of skin and myocutaneous flaps. In clinical practice, application of this technique may lead to improved survival during pedicled or free transfer of myocutaneous flaps and free transfer of skin flaps.

Fate of the TRAM flap after abdominoplasty in a rat model

During a classical abdominoplasty, all musculocutaneous perforators from the deep inferior epigastric vessels are normally divided. Even if somehow neovascularization could relink the abdominal skin and rectus abdominis muscles, reestablishing these same discrete perforators would be unlikely because of the barrier effect of the abdominal wall fascia. Therefore, a lower transverse rectus abdominis musculocutaneous (TRAM) flap intuitively should not regain sufficient vascularity for viability after a prior abdominoplasty, and a history of the latter should be expected to be a major contraindication for this procedure. Nevertheless, anecdotal observations of successful lower TRAM flaps following abdominoplasty seem to contradict our basic principles, which may need better further elucidation. Consequently, this two-stage study in Sprague-Dawley rats was undertaken, initially performing an abdominoplasty in all rats. This was followed 1 or 10 months later by the creation of an unipedicled superiorly based TRAM flap that incorporated virtually all of the abdominal skin. From our identical historical TRAM flap control (n = 5) except without prior abdominoplasty, 72.8 +/- 12.83 percent of this area survived. TRAM flaps raised 1 month after the abdominoplasty (n = 6) had 2.2 +/- 3.4 percent or essentially no viability. Unexpectedly, the long-term group (n = 7) demonstrated 13.7 +/- 10.0 percent viability, ranging from 0 to 30 percent. Both groups of TRAM flaps after abdominoplasty had a flap survival area significantly less than that of the control by two-tailed group t test (p < 0.001), and that of the long-term group area was significantly greater than that of the short-term (p = 0.022). Lead oxide studies 10 months after abdominoplasty revealed no irrefutable evidence of the reestablishment of rectus abdominis perforators to the integument, although obviously some reconnections had formed at the microcirculatory level to partially revascularize some flaps. The range of viability of the long-term rat TRAM flaps documented that for the majority, surviving surface area was minuscule even following a delay equivalent to a human decade after abdominoplasty (1 rat month - 1.1 human years), yet rarely sufficient revascularization did indeed occur, which could explain the prior unusual clinical successes. However, the basic principle that a TRAM flap raised following a classical abdominoplasty at any time would be a risky maneuver seems to still be a valid concept.

TRAM flap perforator ligation and the delay phenomenon: development of an endoscopic/laparoscopic delay procedure

Despite its versatility in breast reconstruction, the TRAM flap is at times subject to ischemic compromise, especially in certain high risk populations. A preoperative delay procedure can decrease the likelihood of TRAM flap failure or fat necrosis, but the required extent of this delay procedure is not clearly defined. In an attempt to augment flap vascularity while reducing surgical dissection and morbidity, six distinct delay procedures and a nondelayed control were compared in a rat TRAM flap model (n = 8 for all groups). An important feature that was incorporated into several groups was the ligation of the contralateral rectus perforators through minimal skin incisions (endoscopic analogy, groups 4 to 7). The most effective delay procedure was the combination of contralateral rectus perforator ligation and ipsilateral dominant pedicle ligation (group 7), which was achieved with two minimal skin incisions and no significant flap undermining. This procedure reduced the flap necrosis from 63.2 +/- 5.8 percent (control) to 13.5 +/- 3.3 percent (p < 0.001). After completion of the animal studies, clinical application of a "minimally invasive" TRAM flap delay procedure was then undertaken in eight high risk patients with only modest ischemic compromise. Although the clinical experience is too early to draw definite conclusions, we feel that "endoscopic delay" has potential as a modality that will increase flap vascularity but minimize the morbidity of the preliminary procedure.

Timing, magnitude, and utility of surgical delay in the TRAM flap: I. Animal studies

Surgical delay is an effective technique, but the precise timing of the delay effect and the required extent of the delay procedure are uncertain. We endeavored to study flap survival as a function of the duration of the delay period in a rat transverse rectus abdominis myocutaneous (TRAM) flap model. Two specific delay procedures (limited and extensive) were utilized, and flap survival was assessed after delay periods of 3, 7, 10, 14, 21, and 30 days (n > or = 7, all groups). A delay of 7 days or greater resulted in statistically significant improvement in flap survival in all groups. The delay effect appeared to be maximal at 14 days, and in the extensive delay group, a 14-day delay resulted in statistically greater flap survival than a 7-day delay. Improvement in flap survival was greater when an extensive delay procedure was used. Although the model system has limitations, the rat TRAM flap appears to be a suitable model for the study of the delay phenomenon. Possible clinical correlations are addressed in part II.