The dorsal skin-flap model in the rat: factors influencing survival

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.

The Influence of Different Irradiation Regimens on Inflammation and Vascularization in a Random-Pattern Flap Model

BACKGROUND

Irradiation plays an important role in the oncological treatment of various tumor entities. The aim of the study was to investigate the influence of different irradiation regimens on random-pattern flaps at the molecular and histopathological levels.

METHODS

Twenty-five rats underwent harvesting of bilateral random-pattern fasciocutaneous flaps. The right flaps received irradiation, while the left flaps served as non-irradiated intraindividual controls. Five rats served as a non-irradiated control group. Four different irradiation regimens with give rats each were tested: 20 Gy postoperatively, 3 × 12 Gy postoperatively, 20 Gy preoperatively, and 3 × 12 Gy preoperatively. Two weeks after surgery, HE staining and immunohistochemical staining for CD68 and ERG, as well as PCR analysis to detect Interleukin 6, HIF-1α, and VEGF, were performed.

RESULTS

A postoperative cumulative higher dose of irradiation appeared to result in an increase in necrosis, especially in the superficial layers of the flap compared to preoperative or single-stage irradiation. In addition, we observed increased expression of VEGF and HIF-1α in all irradiation groups.

CONCLUSION

Even though no statistically significant differences were found between the different groups, there was a tendency for fractional postoperative irradiation with a higher total dose to have a more harmful effect compared to preoperative or single-dose irradiation.

Time-related variations in viability of random pattern skin flaps: An experimental study in rats

Chronobiological variations are in the fabric of life. The first ideas regarding the possible effects of circadian rhythm on surgical outcomes were published in the early 2000s. Some studies support and oppose this idea. The lack of experimental evidence in a controlled setting has led to this study. This study aimed to explore the chronobiological implications of surgical outcomes. The rats were divided into four groups. A random pattern dorsal skin flaps were elevated in all groups at six h intervals. Flap necrosis rates and melatonin, oxidant, and antioxidant factors were studied. Flap survival was better in the 06:00 h group. The flap necrosis was higher in the 18:00 h group. Some of the biochemical parameters displayed circadian variations. As an independent variable, the time of surgical intervention changed the flap survival rates. It should be noted that the study was held in a nocturnal animal model thus the pattern of flap survival can be in reversed fashion in a clinical scenario. This study is the first experimental evidence for "Chronosurgery" in a controlled setting. Further studies in all aspects of surgical disciplines are required.

Standardization of the Rat Dorsal Random Pattern (McFarlane) Flap Model and Evaluation of the Pharmacological Agents Aiming to Salvage Partial Flap Necrosis: A Systematic Review and a Meta-analysis

INTRODUCTION

Partial flap necrosis is a common complication after surgery. McFarlane flap model has been used for assessment of various agents' effects on random flap survival. The aim of this study was to review the methodology of studies using this flap model and reveal the most successful agents.

MATERIALS AND METHODS

PubMed, Scopus, and Web of Science databases were screened for words "McFarlane flap," "flap survival," and ("flap" and "rat") by using time limits between 1965 and 2019. A total of 71 original articles were reviewed. Dimensions and base (cranial/caudal) of the flap, treatment protocol, follow-up period, and survival rates were extracted. Modified survival rates were calculated. Coefficients of variation of cranial/caudally based control group flaps and most commonly used flap models were calculated to assess interstudy variability.

RESULTS

A total of 165 different treatment regimens were studied. One-hundred twelve regimens (67.9%) were found to increase flap survival. Most common flap dimensions were 9 cm × 3 cm, followed by 10 cm × 3 cm, 8 cm × 2 cm and 6 cm × 2 cm. Studies using caudally based flaps showed less interstudy variability, but survival rates were similar. Pentoxifylline, sildenafil, chlorpromazine, phenoxybenzamine, and phentolamine were reported to be successful in multiple studies.

CONCLUSIONS

There are numerous agents found to be effective for treatment of partial flap necrosis, but further clinical research is needed. To overcome standardization problems, use of commonly used flap dimensions with a caudal base and interpretation of results after 7 days of follow-up seems appropriate.

The beneficial effects of subcutaneous Allium cepa injection on random flap survival in rats

Random flaps are frequently used in the practice of reconstructive surgery. The aim of this experimental study was to investigate the effects of Allium cepa on random flap survival in rats. Fourteen Wistar rats were used for this experimental study. The subjects were divided into experiment and control groups. Rats in the experiment group received daily injections of A. cepa extract for 7 d before the elevation of the flaps. Following the treatment period, elevation and reinsertion of the dorsal flaps were performed. Necrotic and total flaps areas were marked and calculated 7 d after the flap elevation. Histological examinations and microangiography were performed to evaluate the results. The mean value of the proportion of necrotic flap areas to the total flap area was 25.06 and 50.6% in the A. cepa and control group, respectively (p = .0079). In the histological examination, number of vessels identified in the dermis were 23.75 ± 0.7 and 33.75 ± 9 in the A. cepa and control group, respectively (p = .7457). In angiographic images, vessels formations were more noticeable in the A. cepa group. We conclude that preoperative subcutaneous A. cepa injection increases dorsal flap survival in rats.

Subdermal nitrous oxide delivery increases skin microcirculation and random flap survival in rats

Random skin flaps are essential tools in reconstructive surgery. In this study, we investigated the effect of subdermal nitrous oxide (N₂O) application on random flap survival. In this experimental study, we used 21 female rats in three groups. In the N₂O and air groups, gases were administrated under the proposed dorsal flap areas daily for seven days. Following the treatment period, flaps were raised and inserted back into their place from the dorsal skin. In the control group, the flaps were elevated and inserted back to their place without any pretreatment. Calculation of necrotic flap areas, histological examination and microangiography was performed to evaluate the results 7 days after the flap surgery. The average of necrotic flap area in the N₂O, air and control group was 13.45%, 37.67% and 46.43%, respectively. (N₂O vs air p = .044; N₂O vs control p = .003). The average number of capillary formations identified in the histological analysis was 7.0 ± 1.58, 3.75 ± 2.36 and 4.4 ± 0.54 in the N₂O, air and control group, respectively. (N₂O vs air p = .017; N₂O vs control p = .037). The average number of capillary structures identified in the angiography images were 6.3 ± 1.52, 1.6 ± 1.15 and 1.3 ± 0.57 in the N₂O, air and control group, respectively. (N₂O vs air p = .04; N₂O vs control p = .02). We conclude that subdermal N₂O application increases random flap survival through an increase in the skin microcirculation and could be promising for future clinical applications.

Dual-axis optical coherence tomography for deep tissue imaging

We have developed dual-axis optical coherence tomography (DA-OCT) which enables deep tissue imaging by using a novel off-axis illumination/detection configuration. DA-OCT offers a 100-fold speed increase compared with its predecessor, multispectral multiple-scattering low coherence interferometry (ms2/LCI), by using a new beam scanning mechanism based on a microelectro-mechanical system (MEMS) mirror. The data acquisition scheme was altered to take advantage of this scanning speed, producing tomographic images at a rate of 4 frames (B-scans) per second. DA-OCT differs from ms2/LCI in that the dual axes intersect at a shallower depth (∼1  mm). This difference, coupled with the faster scanning speed, shifts the detection priority from multiply scattered to ballistic light. The utility of this approach was demonstrated by imaging both ex vivo porcine ear skin and in vivo rat skin from a McFarlane flap model. The enhanced penetration depth provided by the DA-OCT system will be beneficial to various clinical applications in dermatology and surgery.

Viability of randomized skin flaps-an experimental study in rats

BACKGROUND

Randomized skin flaps are extensively used in plastic surgery, but the possibility of necrosis has challenged their use. Several studies have been conducted aiming to find ways to reduce the occurrence of necrosis. We evaluated the effects of pentoxifylline (PTX) and hyaluronidase (HLD), each alone or combined, on randomized rat skin flaps.

MATERIALS AND METHODS

Fifty male Wistar rats were divided into five groups of 10 animals each: control I, control II, PTX, HLD, PTX-HLD. Substances were administered from the first to the 14th postoperative day. The necrotic area was measured on the seventh and 14th postoperative day; the animals were killed on the 14th day, when samples were collected for histologic and immunohistochemical examination.

RESULTS

On the seventh day, percentage of the necrotic area was significantly reduced in PTX, HLD, and PTX-HLD animals compared with control groups. On 14th day, percentage of the necrotic area in PTX, HDL, and PTX-HLD groups was also significantly reduced compared with control groups. PTX and PTX-HLD showed a significant reduction in dermis cellularity, V_V of macrophages, and myofibroblasts compared with control groups; PTX showed a significant enhancement of L_V of blood vessels compared with all other groups.

CONCLUSIONS

The use of each substance alone or combined increased flap viability compared with control groups. On the seventh day, PTX exhibited lower viability than HLD, whereas on the 14th day there was no difference between treated groups. PTX alone enhanced the L_V of blood vessels, whereas PTX-HLD did not. However, PTX-HLD was more effective in decreasing the dermis cellularity and macrophage V_V than HLD alone.

Comparison of Laser Doppler and Laser-Assisted Indocyanine Green Angiography Prediction of Flap Survival in a Novel Modification of the McFarlane Flap

BACKGROUND

The McFarlane rat ischemic dorsal skin flap model has been commonly used for clinical vector studies, as well as the testing of noninvasive diagnostics. However, variability of this model secondary to flap contact with the wound bed has led many to question its validity. Here we present a novel modification to the McFarlane skin flap using sterile silicone. We also use this model to test the prognostic efficacy of laser-assisted indocyanine green (ICG) angiography and laser Doppler imaging (LDI).

METHODOLOGY

A 3 × 9-cm dorsal skin flap with a cranially based pedicle was created, centered 1 cm distal to the scapulae. The flap was undermined, and in one of the 2 groups, a sterile silicone sheet was placed onto the wound bed. All flaps were then reapproximated with sutures 1-cm intervals. Clinical assessment and perfusion imaging was performed immediately postoperative, and at 24, 48, and 72 hours postsurgery. Postoperative day 7 clinical assessment was obtained before euthanasia.

RESULTS

A comparative study using silicone blocked versus unblocked models (n = 6 per group) showed that, clinically, both models had equivalent flap survival [8.5 (0.913) vs 9.5 (1.01) cm]. However, a statistically significant increase in perfusion in the mid-third of unblocked models was observed on POD3 [20.28% (2.7%) vs blocked 13.45% (2.5%), P < 0.05], with a similar increase in the distal third on POD7 [18.73% (2.064%) vs 10.91% (4.19%), P < 0.05]. A prognostic study comparing LDI and ICG angiography prediction of POD7 survival at early time points (n = 10) found that LDI underpredicted flap survival at early time points [84.2% (12.03%) on POD0, 87.35% (16.11%) on POD1]. In contrast, ICG was more proficient [100.1% (10.1%) on POD0].

CONCLUSIONS

We present a modification of the McFarlane skin flap model that results in similar clinical results, but with a noted reduction in perfusion inconsistencies noted in unblocked models. The ICG angiography is superior to LDI in predicting POD7 flap necrosis within the first 48 hours postinjury. Future work will focus on histologic validation of our model, and vector efficacy testing.

Drug-Induced Atrial Fibrillation Complicates the Results of Flap Surgery in a Rat Model

The relationship between atrial fibrillation (AF) and flap survival has not been fully characterized. Therefore, the goal of this study was to investigate the effect of AF on survival areas of pedicled flap and survival rates of free flap in an experimental rat AF model. An aconitine-induced rat AF model was established without intubation anesthesia. Survival areas of the pedicled rectangular epigastric flap were compared between AF rats (n = 7) and control rats (n = 7), and survival rates of the free epigastric flap were compared between AF rats (n = 10) and control rats (n = 10). Animals that died during the study or in which AF was not induced were excluded from study. A total of 64 rats were assessed in this study. Atrial fibrillation was induced with a success rate of 77.8% (21/27) throughout the study. Pedicled flap survival area was significantly higher in controls (75.1 ± 9.0%; n = 7) than that in AF animals (55.7 ± 13.0%; n = 7) (P < 0.01, nonpaired Student t test). Free flap survival rates were 80% in controls and 40% in AF animals (P = 0.07, χ² test). This is the first study to develop an aconitine-induced model of AF in rats. Atrial fibrillation has a detrimental effect on survival areas of the pedicled flap and survival rates of the free flap.

The Vasodilator Effect of a Cream Containing 10% Menthol and 15% Methyl Salicylate on Random-Pattern Skin Flaps in Rats

Background

It is still difficult to prevent partial or full-thickness flap necrosis. In this study, the effects of a cream containing menthol and methyl salicylate on the viability of randompattern skin flaps were studied.

Methods

Forty female Sprague-Dawley rats were divided into two equal groups. Caudally based dorsal random-pattern skin flaps were elevated, including the panniculus carnosus. In the study group, 1.5 mL of a cream containing menthol and methyl salicylate was applied to the skin of the flap, and saline solution (0.9%) was used in the control group. Upon completion of the experiment, flap necrosis was analyzed with imaging software and radionuclide scintigraphy. Histopathological measurements were made of the percentage of viable flaps, the number of vessels, and the width of the panniculus carnosus muscle.

Results

According to the photographic analysis, the mean viable flap surface area in the study group was larger than that in the control group (P=0.004). According to the scintigrams, no change in radioactivity uptake was seen in the study group (P>0.05). However, a significant decrease was observed in the control group (P=0.006). No statistically significant differences were observed between the groups in terms of the percentage of viable flaps, the number of vessels, or the width of the panniculus carnosus muscle (P>0.05).

Conclusions

Based on these results, it is certain that the cream did not reduce the viability of the flaps. Due to its vasodilatory effect, it can be used as a component of the dressing in reconstructive operations where skin perfusion is compromised.

The effects of epinephrine and dobutamine on skin flap viability in rats: a randomized double-blind placebo-controlled study

BACKGROUND

Intraoperative reduction in arterial pressure may cause hypoperfusion of skin flaps, which may increase the risk of flap failure. There is no international consensus regarding the use of vasoactive or inotropic agents to restore or maintain flap perfusion. The purpose of this study was to evaluate the effects of the intraoperative administration of epinephrine and dobutamine on axial-pattern skin flap survival in rats.

METHODS

Fifty-four Sprague Dawley rats were randomized into three groups (n = 18). A tubed axial-pattern skin flap was performed. Animals were randomized to receive an intraperitoneal injection of epinephrine 0.1 mg/kg, dobutamine 0.3 mg/kg, or saline (0.5 ml). The rats were euthanized after 7 days and the viable area of the flap was compared between the groups using a digital imaging and computer software.

RESULTS

Seven rats/flaps were excluded from the study due to autocannibalism (n = 3), postoperative tracheal obstruction (n = 2), anesthesia-induced respiratory arrest (n = 1), and abnormal behavior requiring euthanization (n = 1). The mean flap survival was 46% ± 9% in the saline group (n = 17), 41% ± 9% in the epinephrine group (n = 14) (p = 0.088 compared to the saline group), and 54% ± 9% in the dobutamine group (n = 16) (p = 0.02 compared to the saline group and p = 0.001 compared to the epinephrine group).

CONCLUSIONS

Intraoperative intraperitoneal injection of dobutamine improves skin flap survival in rats, whereas intraperitoneal epinephrine tends to decrease skin flap survival.

Effects of nebivolol on skin flap survival: A randomized experimental study in rats

BACKGROUND

Skin flaps are among the basic treatment options in the reconstruction of soft tissue defects. To improve skin flap survival, a variety of methods, including pharmacologic agents, have been investigated. The effectiveness of anticoagulants, antioxidants, anti-inflammatory drugs, and vasodilatory drugs in improving flap survival has been studied. Nebivolol is a new-generation selective β1-adrenoreceptor blocking agent that has vasodilatory, antithrombotic, antioxidative, and anti- inflammatory effects.

OBJECTIVE

The aim of this experimental study was to investigate the effects of nebivolol (50 mg/kg/d) on random pattern skin flap survival in rats.

METHODS

Male Wistar rats weighing 290 to 310 g were randomly divided into 2 groups-the nebivolol group and the control group. Random patterned, caudally-based, ~3 × 10-cm skin flaps were elevated on the back of each rat. In the nebivolol group, nebivolol 50 mg/kg/d (1 mL, of a racemic solution of nebivolol) was administered orally 2 days before surgery to reach steady-state drug blood concentrations and was continued for 6 days. In the control group, 1 mL/d of sterile saline solution was orally administered 2 days before surgery and was continued for 6 days. To observe the effects of nebivolol, cutaneous blood flow was examined using a laser Doppler flow-meter before and after surgery on days 1, 3, 5, and 7, and flap tissue, malondialdehyde (MDA) and glutathione (GSH) concentrations, and superoxide dismutase (SOD) activity were measured 7 days postsurgery. Flap viability was evaluated 7 days after surgery by measuring necrotic flap area and total flap area.

RESULTS

All 20 rats (nebivolol group, n = 10; control group, n = 10) survived throughout the study period. Mean (SD) MDA concentration was significantly lower in the nebivolol group than in the control group (69.25 [5.82] vs 77.67 [6.87] nmol/g tissue; P = 0.009). GSH concentration was significantly higher in the nebivolol group than in the control group (2.14 [0.15] vs 1.88 [0.22] nmol/mg tissue; P = 0.004). SOD activity was significantly greater in the nebivolol group than in the control group (49.28 [5.49] vs 42.09 [4.95] U/g tissue; P = 0.007). The percentage of the flap that was necrotic was significantly lower in the nebivolol group than in the control group (40.27 [4.08] vs 48.87 [6.35]; P = 0.007).

CONCLUSIONS

This small, experimental, in vivo animal study found that nebivolol was associated with reduced necrotic random pattern skin flap area. Further studies are needed to clarify these findings.

The effect of prophylactic doses of nadroparin and therapeutic doses of betamethasone on skin flap survival in rats

Application of pedicle flaps is of great importance in orthopaedics and reconstructive surgery. It has been postulated that anticoagulants or anti-inflammatory treatments may have advantageous effect on pedicle flap survival. The aim of this study was to investigate whether: 1. low-molecular-weight heparin given at prophylactic doses or 2. steroids given at therapeutic doses improve survival of dorsal pedicle flap in rats. Thirty four animals divided into three groups were used for the experiments: Group I (N=12) was treated with low-molecular-weight heparin (nadroparin, 40 IU per kilogram of body mass/day). Group II (N=12) received single injection of betamethasone (intramuscularly, 0.1 mg per kilogram of body mass). Group III (N=10) received sterile saline (0.9% NaCl) subcutaneously as placebo. All animals were housed individually in an environmentally controlled room. After seven days from the operation, 51.7% of the dorsal flaps survived in group I and 48.3% in the group II. These results were comparable to those in the control animals. Our results indicate that neither low dose heparin (nadroparin) used at prophylactic doses nor steroids used at therapeutic doses had any effect on dorsal pedicle flap survival in rats.

The Effect of Fibrin on the Survival of Ischemic Skin Flaps in Rats

BACKGROUND

Skin flap necrosis is one of the hazards encountered in plastic and reconstructive surgery. Angiogenic agents may be useful for treating it by increasing blood flow. The angiogenic effect of fibrin in vitro has been demonstrated, but little is known about its in vivo effect. Te authors tested the hypothesis that local application of fibrin can improve the survival of ischemic skin flaps.

METHODS

A cranially based dorsal skin flap (3 x 7 cm) was made in each rat. Fibrin (8 mg suspended in 400 microl of phosphate-buffered saline) was applied to the subcutaneous side of elevated skin flaps in the experimental group (n = 15), and phosphate-buffered saline alone was delivered in the control group (n = 15). Tissue blood flow of the skin flaps was measured four times (before the operation and on days 1, 3, and 7) at 1, 3, and 5 cm distal to the baseline of the skin flap. The survival rate of the skin flaps was measured on day 7 and histologic assessments were performed.

RESULTS

The blood flow change rate at 5 cm in the experimental group was significantly higher than that in the control group on day 7 (60.9 +/- 5.7 percent versus 13.7 +/- 4.8 percent, p < 0.001). The survival rate of skin flaps was also significantly improved in the experimental group (77.0 +/- 2.0 percent) in comparison with the control group (54.7 +/- 2.2 percent, p < 0.01). Histologic analysis showed many more blood vessels in the experimental group in comparison with the control group.

CONCLUSION

The local application of fibrin could improve the blood flow and survival of ischemic skin flaps.

Murine skin flap survival may not be affected by underlying fat viability

One problem in the treatment of degloving injuries is the accurate prediction of the survivability of the avulsed tissue. Initial evaluation frequently underestimates the degree of eventual flap loss, and in many cases, there is a progressive necrosis that continues over the ensuing days. The pathophysiology of this phenomenon is unclear. We undertook this study to test the theory that underlying devascularised fat contributes to overlying skin necrosis. A dorsal random skin flap model was used in the rat. Sixty-six rats were divided into three groups: flaps with viable fat and silicone sheeting underneath, flaps with devascularised fat and silicone sheeting underneath and control flaps with only silicone sheeting underneath. Flap necrosis (% area+/-SEM) was evaluated at one week, and found to be 27.1+/-4% in the live fat group, 33.2+/-4% in the dead fat group and 33.6+/-5% in the control group. One-way analysis of variance showed no statistically significant difference between the three groups at a power of 80%. In this study, we have shown that neither live nor dead fat has a significant influence on the survival of an overlying random skin flap in the rat.

The Effect of Hyperbaric Oxygen Therapy on the Delay Procedure

BACKGROUND

This study evaluates the possibility of enhancing the beneficial effect of the delay procedure by using hyperbaric oxygen therapy, and the possibility of lessening the time required for maximal effect of delay procedure.

METHODS

Eight male Wistar rats were used in each of 10 groups. The surgical delay method was applied to the caudally based dorsal rat flap by incising the longitudinal borders and undermining the flap. In the first five groups, 3-, 7-, 10-, 14-, and 21-day delay periods were applied, and in the other five groups, hyperbaric oxygen therapy was applied during the delay periods. Blood circulation was measured with a laser Doppler flowmeter, and flap survival lengths were recorded. Histological analysis for vascular counting and determining vascular areas and microangiographic analysis for monitoring vascular status were performed.

RESULTS

In addition to the flap viabilities being increased, the maximum effect of the delay procedure could be achieved earlier with hyperbaric oxygen therapy. Blood circulation in the flaps, vascular counts, and vascular areas were increased by applying hyperbaric oxygen during the delay period. Microangiographic results confirmed the beneficial effect of hyperbaric oxygen treatment.

CONCLUSIONS

Hyperbaric oxygen treatment during the delay period can lessen the time period needed for the delay procedure and increase the effect of the delay itself.

Effects of nitric oxide synthase inhibition on blood flow and survival in experimental skin flaps

The aim of the present study was to examine the effect of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME) on skin and flap blood flow, NOS activity and flap survival in an ischaemic dorsal flap model in the rat. Fifty-four rats were used in the study. l-NAME or the inactive enantiomere d-NAME was given intravenously either pre-, per- and postoperatively or only postoperatively. Controls received saline treatment. Blood pressure and skin and flap blood flow were monitored. NOS activity was measured in intact skin before and after l-NAME and d-NAME infusion and in flap tissue 48h postoperatively. Forty-eight hours postoperatively flap survival was determined in all rats. l-NAME treatment caused: (1) a marked attenuation of constitutive Ca(2+) dependent NOS activity in intact skin (p<0.001), (2) an increase in blood pressure (p<0.05), (3) a decrease in blood flow in intact skin and in skin flaps (p<0.05), and (4) a decrease in flap survival (p<0.05). In saline and d-NAME treated animals no change in blood pressure, blood flow or NOS activity in intact skin was noted. In conclusion this study shows that l-NAME attenuates constitutive Ca(2+) dependent NOS activity in intact skin, decreases skin and flap blood flow and decreases the survival of skin flaps. These results indicate that constitutive nitric oxide synthase is important for basal blood flow in skin and flap tissue and for the survival of skin flaps.

Thrombospondin-1 limits ischemic tissue survival by inhibiting nitric oxide-mediated vascular smooth muscle relaxation

The nitric oxide (NO)/cGMP pathway, by relaxing vascular smooth muscle cells, is a major physiologic regulator of tissue perfusion. We now identify thrombospondin-1 as a potent antagonist of NO for regulating F-actin assembly and myosin light chain phosphorylation in vascular smooth muscle cells. Thrombospondin-1 prevents NO-mediated relaxation of precontracted vascular smooth muscle cells in a collagen matrix. Functional magnetic resonance imaging demonstrated that an NO-mediated increase in skeletal muscle perfusion was enhanced in thrombospondin-1-null relative to wild-type mice, implicating endogenous thrombospondin-1 as a physiologic antagonist of NO-mediated vasodilation. Using a random myocutaneous flap model for ischemic injury, tissue survival was significantly enhanced in thrombospondin-1-null mice. Improved flap survival correlated with increased recovery of oxygen levels in the ischemic tissue of thrombospondin-1-null mice as measured by electron paramagnetic resonance oximetry. These findings demonstrate an important antagonistic relation between NO/cGMP signaling and thrombospondin-1 in vascular smooth muscle cells to regulate vascular tone and tissue perfusion.

Nonsurgical Delay of Dorsal Rat Cutaneous Flap Using a Long-Pulsed 1064-nm Nd:YAG Laser with a Contact Cooling Device

BACKGROUND

This study evaluated the efficiency of a long-pulsed neodymium:yttrium-aluminum-garnet laser, operating at 1064 nm and equipped with a contact cooling device, in the delay of a caudally based dorsal rat skin flap (10 x 3 cm). This laser has deeper tissue penetration and has not been used for this purpose before.

METHODS

Twelve male Sprague-Dawley rats were used in each of six groups. The delay effects of three different laser treatment patterns (only longitudinal borders, cephalic and longitudinal borders, and entire surface of the 10 x 3-cm flap) were compared with an acute untreated control flap as well as two surgical delay methods (incision of longitudinal borders and incision of longitudinal borders plus flap undermining). The laser effects on the cutaneous vasculature and perfusion were assessed by intravenous fluorescein injection, histologic study, microangiography, and in vivo real-time video monitoring.

RESULTS

Selective thermocoagulation of subdermal vessels was achieved using a 6-mm spot, 140-J/cm fluence, and 40-msec pulse width. In the cephalic and longitudinal borders laser-treated group, a delay effect was achieved. The maximum delay effect was achieved by the surgical delay group that used the method of incision of the longitudinal borders plus flap undermining. Laser treatment of only the longitudinal borders did not improve flap survival, whereas treatment of the entire flap surface significantly reduced flap survival.

CONCLUSION

Nonsurgical delay of a dorsal rat cutaneous flap is possible by selective occlusion of the subdermal plexus at the longitudinal and cephalic borders of the planned flap using a long-pulsed 1064-nm neodymium:yttrium-aluminum-garnet laser equipped with a contact cooling device.

Evaluation of Flashlamp-Pumped Pulsed-Dye Laser (585 nm) in Nonsurgical Delay of Dorsal Rat Cutaneous Flaps

BACKGROUND

This study evaluated the efficiency of a flashlamp-pumped pulsed-dye laser operating at 585 nm in the delay of a caudally based, 10 x 3-cm dorsal rat skin flap. Two different laser treatment patterns (only longitudinal borders and the entire surface of the proposed flap) for two different fluences (6 J/cm and 8 J/cm) were compared with an acute untreated control flap as well as two surgical delay methods (incision of longitudinal borders and incision of longitudinal borders plus flap undermining).

METHODS

Twelve male Sprague-Dawley rats were used in each of seven groups. Two additional rats were used for histologic evaluation and two rats were used for in vivo real-time video monitoring studies. Two weeks after delay procedures, the flaps were raised and sutured on the primarily closed flap donor area. After 5 days, the length of flap survival was measured. The effects of the laser on the cutaneous vasculature and perfusion were assessed by intravenous fluorescein injection, histologic analysis, microangiography, and in vivo real-time video monitoring.

RESULTS

No statistically significant improvement in flap survival was observed in any of the laser treatment groups.

CONCLUSIONS

The overall findings indicate that the flashlamp-pumped pulsed-dye laser operating at 585 nm did not penetrate deep into skin and coagulate the subdermal plexus with tested laser settings and did not induce the delay phenomenon.

Effect of vascular endothelial growth factor-induced angiogenesis on TRAM flap harvesting after abdominoplasty

In this study, the effect of intramuscular injection of human vascular endothelial growth factor (hVEGF) on neovascularization following abdominoplasty was investigated. Twenty-four Sprague-Dawley rats were divided into four groups (n = 6). Two control groups and two experimental groups were established. Abdominoplasty was performed in all rats, with division of all the perforator vessels. In the control groups, normal saline was injected into the rectus abdominis muscle, and in the experimental groups, 100 microg of VEGF and normal saline were injected into the rectus muscle. A transverse rectus abdominis musculocutaneous (TRAM) flap was harvested on day 20 and day 40 in both the control and experimental groups. The range of viability of the TRAM flap was, respectively, 0 to 20 percent (mean, 6.7 percent) and 0 to 25 percent (mean, 14.2 percent) in both short-term and long-term control groups (no VEGF injected). The study (VEGF) group demonstrated a viability of 50 to 80 percent (mean, 70 percent) for the short-term group and 50 to 85 percent (mean, 72.5 percent) in the long-term group. No wound infection was documented, and there were no deaths during the study period. There was no statistically significant difference between the short-term and long-term divisions of the groups (p < 0.01); however, significant differences were observed between the control and experimental groups (p < 0.01). The authors concluded that VEGF injection after abdominoplasty improved the percentage of TRAM flap viability. This method of delay/revascularization could be used for the difficult problem of flap viability following abdominoplasty and for high-risk patients.

The effect of capillary ultrafiltration probes on skin flap edema

OBJECTIVE

Edema clearly has deleterious effects on the microcirculation and, consequently, cell viability. Prior work from this laboratory demonstrated that hyperosmolar microdialysis can reduce tissue edema, but this method is technically challenging. A new, simpler technique of microdialysis using capillary ultrafiltration probes (CUPs) has been studied to determine if CUP microdialysis is as effective in reducing tissue edema in the same animal model.

METHODS

Twenty-four Sprague-Dawley rats were studied using a modified McFarlane skin flap. Microdialysis was accomplished using a catheter constructed of four 4-cm hollow fibers that were connected to polyethylene tubing. Catheters on the experimental side of the flap were attached to a vacuum manifold for 8 hours. The control side was treated in 2 ways. In group 1, catheters were placed but not applied to suction. In group 2, no catheters are placed on the control side. Tissue water content was determined by a biopsy-drying technique.

RESULTS

Tissue water content was significantly reduced (by paired t test) in both groups by a mean of 3.2 mL/100 g of wet tissue.

CONCLUSION

CUP microdialysis reduced tissue water content as effectively as did hyperosmolar microdialysis, but in a simpler and therefore more cost-effective method. The technique could be easily adapted for clinical application.

Thrombin peptide TP508 accelerates closure of dermal excisions in animal tissue with surgically induced ischemia

TP508 is a synthetic peptide corresponding to amino acids 508 through 530 of human prothrombin. We previously demonstrated that a single topical application of TP508 stimulates revascularization and healing of acute incisional and excisional wounds in normal, healthy rat skin. To determine if TP508 would enhance wound healing in ischemic skin, we used bipedicle flaps, cranially based flaps, and free grafts to surgically create ischemic regions on the backs of rats. Full-thickness, circular excisions were made within the flaps or grafts and immediately treated with a single application of saline +/- TP508 (0.1 microg/wound). Compared to wound closure in normal skin, ischemic skin wounds exhibited delayed closure, and the length of delay correlated with the degree of surgically induced ischemia. TP508 significantly accelerated closure in both normal and ischemic skin, resulting in closure rates that were increased within the first 7 days of wounding by 30% in normal tissue and bipedicle flaps, 50% in cranially based flaps, and 225% in free grafts. Moreover, in both flap models, TP508 restored the rate of closure to a rate approximating the control rate observed in normal skin. Histological comparisons of wound tissue from normal skin and cranially based flaps showed that ischemia reduced early recruitment of inflammatory cells at day 1 but increased inflammatory cell numbers in wound beds at day 14. TP508 treatment of ischemic flap wounds significantly increased early inflammatory cell recruitment and restored the normal rapid resolution of the inflammatory phase. In addition, at day 7, TP508-treated wounds appeared to have an increased number of large functional blood vessels compared to saline controls. These studies support the potential efficacy of TP508 in treating ischemic wounds in humans.

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.

Amrinone, a selective phosphodiesterase III inhibitor, improves microcirculation and flap survival: a comparative study with prostaglandin E1

BACKGROUND

Amrinone, a selective phosphodiesterase (PDE) III inhibitor, is a newly developed agent that possesses a combination of positive inotropic and vasodilating properties as a result of preventing the degradation of cAMP and it has recently been licensed for treatment of heart failure alone. Amrinone is expected to be useful for the treatment not only of heart failure but also of peripheral circulatory disorders, including vascular disease, and for ischemic flaps, because it improves microcirculatory hemodynamics. To investigate potential therapeutic applications of amrinone, we evaluated its ability to improve microcirculatory hemodynamics and flap survival.

MATERIALS AND METHODS

The rat skinfold chamber technique was employed to quantify microcirculation directly in vivo. The improved survival area of random flaps in rats treated with amrinone was examined to assess therapeutic efficacy of this drug. Its effects were compared with those of prostaglandin E1 (PGE1), which has been widely approved as an agent for improving hemodynamics.

RESULTS

Microcirculatory blood flow and flap survival area were significantly increased in both amrinone- and PGE1-treated animals, compared to the saline-treated controls. The ameliorating effects of amrinone were comparable to those of PGE1.

CONCLUSIONS

The results of this study suggest amrinone to be a potentially useful drug not only for treating heart failure but also for improving microcirculation in patients with vascular diseases and for postoperative care after reconstructive surgery.

Nitric oxide synthase activity and endothelial ultrastructure in ischaemic skin-flaps

The aim of the present study was to detect and quantify nitric oxide synthase (NOS) activity and to investigate morphological changes in the endothelium in two different ischaemic dorsal flap models in the rat, one based cranially and one based caudally. Intact skin from the dorsum was used as control. In both groups flaps were removed at 1, 4, 12, 24 and 72 h after surgery respectively. NOS-activity was measured by the conversion of L-arginine to L-citrulline and endothelial morphology was investigated using transmission electron microscopy. Intact skin showed Ca(2+)-dependent but no Ca(2+)-independent NOS-activity. A time-dependent decrease in Ca(2+)-dependent NOS-activity was seen in the proximal and distal part of the flaps in both flap models and was most pronounced in the distal part. Ca(2+)-independent NOS-activity increased in the proximal and distal part of flaps based cranially and in the proximal part of flaps based caudally. Morphological analysis of the endothelium showed signs of endothelial damage including blebbed membranes, swelling and endothelial loss. These findings show that ischaemia caused by skin-flap surgery leads to endothelial damage and a decrease in Ca(2+)-dependent nitric oxide synthase activity. Furthermore, in the skin-flaps an induction of Ca(2+)-independent nitric oxide synthase (iNOS) activity was noted both in surviving flap tissue and in flap tissue destined to necrose.

Effect of beraprost sodium (Procylin), a stable prostaglandin I2 analogue, on a dorsal skin flap model in rats

Beraprost sodium, a chemically stable prostaglandin I2 analogue with antiplatelet vasodilator actions, was tested by comparing the extent of viability of random pattern skin flaps in control rats and rats treated with beraprost sodium. An isolated tail based 2 x 7 cm flap was constructed in 50 Sprague-Dawley rats. In group 1 (beraprost sodium treated group, n = 25) 0.015 mg beraprost sodium were injected intraperitoneally immediately after the flap had been raised. In group 2 (control group, n = 25) the animals were injected intraperitoneally with the same volume of saline immediately after the flap had been raised. At the end of the seventh day the flap survival area was documented using digital planimetry. The difference between the results showed that beraprost sodium had significantly beneficial effect on skin flap survival (p < 0.01, Welch's test).

Role of perivenous areolar tissue and recipient bed in the viability of venous flaps in the rabbit ear model

This study was performed to investigate the role of perivenous areolar tissue and flap bed in the viability of venous flaps in the rabbit ear model as described by Inada et al. Six groups of flaps were studied: group A--flap based on a proximal vein and areolar tissue; group B--flap based on a proximal venous pedicle which has been skeletonised; group C--flaps based on a proximal vein and areolar tissue sutured over a full thickness skin graft (FTSG), preventing diffusion into the flap; group D--flaps with a skeletonised pedicle sutured over a FTSG; group E--control, non-vascularised flap placed directly on bed; and Group F--control, non-vascularised flap sutured over a FTSG. Groups C and D had 15 flaps and the remaining groups had 10 flaps in each. All flaps in groups A and B had total or partial survival. In group C 4 flaps survived completely, 8 had partial survival and 3 necrosed. Group D had only 2 flaps with partial survival with 13 flaps with total loss. In group E there were 10 flaps with partial survival and none with complete loss. No flaps in group F survived. Histological examination of the pedicle showed small vascular channels present in the areolar tissue surrounding the venous pedicle. This study confirms the importance of the perivenous areolar tissue in the perfusion of the venous skin flap in the rabbit ear model.