Circulatory and metabolic events in pig island skin flaps after arterial or venous occlusion

After 1 hour of arterial or venous occlusion, the circulatory and metabolic events in island skin flaps of the pig were studied. Both occlusion types showed significant but transient increases in glucose uptake and a parallel release of lactate, hypoxanthine, and potassium. Oxygen uptake and noradrenaline release were not significantly affected. No significant difference between the arterial and venous occlusions was seen in the metabolic parameters. The flap blood flow, measured by total venous outflow and laser Doppler flowmetry, was significantly lower after venous than after arterial occlusion. This long-lasting difference in flow response may help to explain the observation that venous occlusion is more deleterious to skin flaps than arterial occlusion. A mechanism underlying these results may be more pronounced microthrombotization and/or edema formation after venous occlusion than after arterial occlusion.     

Circulatory and metabolic changes in expanded pig skin flaps

To evaluate circulatory and metabolic changes in pig skin during tissue expansion, the buttock skin of 12 pigs was expanded for 5 weeks. In a second operation, island buttock flaps were elevated bilaterally. Flap temperature, laser Doppler flow (LDF), and fluorescein penetration borders were recorded. Norepinephrine infusions were given twice. After cannulation of the external iliac veins, the total venous outflow from the flaps and metabolic parameters such as glucose and oxygen consumption and lactate production were measured bilaterally. No significant difference in fluorescein staining was found, but laser Doppler flow in the expanded tissue was higher than in nonexpanded skin, whereas the total flap blood flow was not significantly different. A flow reduction was seen in expanded flaps during norepinephrine infusion, whereas nonexpanded flaps showed a slightly increased blood flow. This adrenergic supersensitivity indicates that it is possible that not only surgical nerve section but also tissue expansion can result in sympathetic denervation. No differences in the metabolic parameters were observed.     

Survival of island flaps after tissue expansion: a pig model

Survival of island flaps after tissue expansion has been studied. Expanders were placed under each buttock flap of six minipigs and one side was expanded while the other was left empty as a control. Both flaps were then raised and isolated on their vascular pedicles in order to compare flap survival 7 days later. It was found that the survival lengths of the expanded flaps were approximately 50 percent greater than those of the delayed controls. Microangiography suggested that the diameter of the axial artery increased following expansion. In clinical practice this technique would provide a larger flap for reconstruction and the possibility of direct closure of the donor site. In addition, the observed increase in vessel caliber should facilitate the free tissue transfer of expanded flaps.     

Prevention of necrosis in island myocutaneous flaps in the pig by treatment with isoxsuprine.

Experimental gracilis myocutaneous flaps were designed in the pig which consistently resulted in 81 cm2 of surviving tissue and 194 cm2 of necrotic tissue. When these same flaps were raised in animals treated for two weeks preoperatively and 6 days postoperatively with isoxsuprine, there was 100 percent survival in all (8) flaps.     

The pig as an experimental animal in plastic surgery research for the study of skin flaps, myocutaneous flaps and fasciocutaneous flaps

The pig serves as an excellent model of skin flap research. Many flap types are available and flap designs can be modified easily for specific experimental requirements. Swine are large enough to permit multiple flaps and the skin color allows subjective observations of tissue circulation.     

Effect of capsulectomy on the hemodynamics and viability of random-pattern skin flaps raised on expanded skin in the pig

Skin flaps constructed on expanded skin usually include the underlying capsular tissue. It has been hypothesized that capsulectomy may jeopardize the viability of the expanded skin flap. The experiments reported herein were designed to test this hypothesis. Specifically, we studied the hemodynamics and viability of random-pattern skin flaps (8 X 20 cm) raised on delayed bipedicle flaps (group A) and on expanded skin pockets with capsulectomy at the time of flap elevation (group B) or with intact underlying capsular tissue (group C). Each group was randomly assigned to each flank in 16 pigs. Skin pockets were expanded by inflation of subcutaneous silicone tissue expanders with sterile saline (299 +/- 7 ml; X +/- SEM) over a period of 3 weeks. At the end of this period, the bipedicle flaps were constructed. Eight days later, random-pattern skin flaps were raised on bipedicle flaps and skin pockets. The length and area of skin flap viability, judged by the fluorescein dye test performed 1 day postoperatively, were not significantly different (p greater than 0.05) among groups A, B, and C (n = 31 to 32). There also were no significant differences (p greater than 0.05) in total skin capillary blood flow measured 1 day postoperatively (A = 2.6 +/- 0.4, B = 2.4 +/- 0.4, and C = 2.7 +/- 0.6 ml/min per flap; n = 15 to 16) and in skin viability assessed 7 days postoperatively (A = 74 +/- 2, B = 75 +/- 2, and C = 76 +/- 2 percent; n = 16) among delayed skin flaps and skin flaps raised on expanded skin pockets with or without capsulectomy. The results of this flap viability study were confirmed in 5 minipigs in a separate experiment. We conclude that capsulectomy did not have a detrimental effect on the hemodynamics and viability of random-pattern skin flaps raised on expanded skin. Furthermore, we hypothesize that skin flaps raised on expanded skin are similar to delayed skin flaps in that the skin blood flow is optimally augmented; therefore, the capsular tissue does not add significant blood supply to the overlying skin.     

Hemodynamics and vascular sensitivity to circulating norepinephrine in normal skin and delayed and acute random skin flaps in the pig

Cutaneous circulation in 4 X 10 cm skin samples and delayed and acute random skin flaps constructed on the flanks of castrated Yorkshire pigs (13.3 +/- 0.7 kg; n = 12) were studied during intravenous infusion (0.5 ml per minute) of 5% dextrose solution (vehicle) and 5% dextrose containing norepinephrine (1 microgram/kg per minute). Total and capillary blood flow and A-V shunt flow were measured by the radioactive microsphere technique 6 hours after the raising of 4 X 10 cm single-pedicle acute and delayed random skin flaps using the technique and calculations published previously. Fluorescein dye test was also performed to assess vascular perfusion. It was observed that the capillary blood flow in the single-pedicle delayed skin flaps was similar to that in the normal skin, and the maintenance of this normal skin blood flow was not due to the closing of A-V shunt flow in the delayed skin flaps. Similarly, the significant (p less than 0.01) decrease in capillary blood flow and distal perfusion in the acute skin flaps compared with the delayed skin flaps was not due to the opening of A-V shunts in the acute skin flaps. There was no evidence to indicate that A-V shunt flow per se was the primary factor for the regulation of capillary blood flow in the acute and delayed skin flaps in the pig. Our data seemed to indicate that tissue ischemia in the distal portion of acute skin flaps was likely the result of vasoconstriction of the small random arteries which supplied blood to arterioles and A-V shunts, and locally released neurohumoral substances may play an important role in the pathogenesis of vascular resistance and ischemia in the acute skin flaps.     

Evaluation of tests for predicting the viability of axial pattern skin flaps in the pig.

The viability of axial pattern skin flaps in pigs was assessed by the use of intravenous fluorescein, intradermal injection of 133Xe in saline, intravenous 51Cr tagged red cells, and angiography. The results were correlated with flap survival at 4 days postoperatively. Intravenous fluorescein provided the most accurate method for prediction of viable tissue at the time of operation. There was no evidence of vascular perfusion in the distal portions of these flaps. These axial pattern flaps differed in their viability from similar flaps in humans, and anastomoses between discrete vascular territories were infrequent in pigskin.     

Subcutaneous bipedicle island flaps on the face

Since 1996, 13 patients have undergone the reconstruction of facial skin defects with subcutaneous bipedicle island skin flaps. The reasons for the surgery were basal cell carcinoma in 10 patients and benign skin tumor excision in three patients. All defects were reconstructed with subcutaneous bipedicle skin flaps without significant complications. Bipedicle subcutaneous skin flaps are a useful alternative for facial reconstruction.     

Effect of glucocorticoid treatment on skin capillary blood flow and viability in cutaneous and myocutaneous flaps in the pig

The effect of methylprednisolone treatment on skin-flap viability and capillary blood flow was studied in a series of four experiments. Intramuscular methylprednisolone injections (30 mg/kg per day), given in single or divided doses preoperatively or postoperatively, had no effect in augmenting skin viability in arterialized cutaneous, myocutaneous, or random skin flaps compared with the control. Capillary blood flow was studied in arterial buttock flaps and latissimus dorsi myocutaneous flaps raised on animals treated preoperatively with methylprednisolone or saline (control), and no significant difference in capillary blood flow was noted between the treatment and control flaps. It was concluded that methylprednisolone has no significant therapeutic effect either in increasing flap viability or in increasing capillary blood flow in skin flaps in pigs.     

Innervated island flaps in morphofunctional vulvar reconstruction

In this article, the authors present their own experience in vulvar reconstruction following vulvectomy using two different innervated island flaps according to the size and site of the defect. Island-flap mobilization is possible thanks to the rich blood supply of the perineal region. The methods described are a "V-Y amplified sliding flap from the pubis" and a "fasciocutaneous island flap" raised from one or both gluteal folds. The V-Y amplified sliding flap from the pubis is indicated when the defect is symmetric and located anteriorly. This flap is harvested from the pubis and vascularized by the deep arterial network of the pubis. Sensory innervation is provided by branches of the ileo-inguinal nerve. The fasciocutaneous island flap, raised from one or both gluteal folds, can be used following hemivulvectomy or radical vulvectomy, respectively, to cover posteriorly located defects. Vascularization is provided by the musculocutaneous perforating branches of the pudendal artery, whereas sensory innervation is maintained through the perineal branches of the pudendal nerve. Twenty-two patients have undergone reconstructive surgery of the vulvar region from 1989 to date. On 14 patients, a V-Y amplified sliding flap was used; on 7 patients, reconstruction was carried out by island flaps raised from the gluteal fold. Both techniques are compatible with inguino-femoral lymphadenectomy, and they allow for a correct morphofunctional reconstruction and provide good local sensibility. The final result is aesthetically satisfactory, as all final scars are hidden in natural folds.     

An evaluation of eight methods of using fluorescein to predict the viability of skin flaps in the pig

The brightness of the fluorescence of fluorescein can be increased by the use of special (interference) filters that allow visualization of the dye when much smaller doses have been given. Standard random-pattern skin flaps were made in pigs and low (1 mg/kg) and high (500 mg) doses of fluorescein were given intravenously. The dye distribution in the flaps was evaluated visually, photographically, and with a dermofluorometer. All the methods proved reasonably accurate in predicting survival, although in an occasional flap, readings by all the methods were off by as much as 3.5 cm. The traditional Wood's lamp visualization proved to be as accurate as any of the newer methods. The inaccuracies of the fluorescein test are probably inherent in the method, since it only measures vascularity at the time the dye is given--and blood supply can change. The main advantage of low-dose fluorescein is that it allows repeated injections at reasonably close intervals. For serial observations, the dermofluorometer is unquestionably the best method.     

Anterolateral thigh fasciocutaneous island flaps in perineoscrotal reconstruction

This study presents the authors' experience using the anterolateral thigh fasciocutaneous flap for complex perineal and scrotal reconstruction. Anterolateral thigh fasciocutaneous island flaps were performed in seven patients between January and June of 2000 (six male, one female; mean age, 52 years; age range, 9 to 72 years). Four of the seven patients had scrotal or perineal defects after multiple debridements for Fournier's gangrene. Two of these four had exposed testicles. Three flaps were used for recurrent ischial ulcers. A true septocutaneous perforator (type 1) running between the rectus femoris and the vastus lateralis muscles was found in only two patients. In four patients, the cutaneous perforators were found to be intramuscular, originating from the descending branch (type 2). In the other patient, the musculocutaneous perforator originated from the lateral circumflex femoris artery independently (type 3). In these cases, intramuscular dissections were performed to follow each perforator to its main trunk. Mean follow-up was 8 months (range, 5 to 10 months), and all flaps survived. Three patients developed minor wound dehiscence in the posterior aspect of the perineal wound because of fecal contamination and skin maceration. Both wounds healed secondarily. Scrotal reconstruction with the anterolateral thigh flap gave an excellent aesthetic result. The authors conclude that the anterolateral thigh flap is a reliable flap for perineoscrotal reconstruction.     

Augmentation of transmidline skin perfusion and viability in transverse rectus abdominis myocutaneous (TRAM) flaps in the pig.

The aim of this experiment was to design a clinically relevant TRAM flap in the pig and to use this flap model to study the effectiveness of preoperative ligation of the dominant vascular pedicle in augmentation of muscle and skin capillary blood flow and skin viability in the TRAM flap. This TRAM flap model was based on the deep inferior epigastric vascular pedicle, with the center of the transverse skin paddle attached to the underlying rectus abdominis muscle at the superior end of the muscle and extending bilaterally from its attached muscle. The transverse skin paddle (8 x 30 cm) included a contralateral and ipsilateral random portion of skin. This flap model was based on the deep inferior epigastric rather than the superior epigastric vascular pedicle because the deep inferior epigastric vascular pedicle is the smaller of the two in the pig and augmentation of its blood supply by ligation of the dominant superior epigastric vascular pedicle resembles more closely the clinical situation. It was observed that ligation of the dominant superior epigastric vascular pedicle 14 days prior to raising the TRAM flap significantly (p less than 0.05; n = 5) increased the total muscle and skin capillary blood flow and skin viability in the transverse skin paddle compared with the sham-operated control (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)     

Augmentation of blood flow in delayed random skin flaps in the pig: effect of length of delay period and angiogenesis

Skin capillary blood flow and angiogenesis were studied by radioactive microsphere and morphometry technique, respectively, in delayed random skin flaps in the pig. Skin flaps were delayed for 2, 3, 4, 6, or 14 days. Blood flow was measured 6 hours after complete raising of acute and delayed random skin flaps on the opposite flanks of the same pig. It was observed that the capillary blood flow increased significantly (p less than 0.05) within 2 days of delay compared to the acute skin flaps. This capillary blood flow further increased by about 100 percent between days 2 and 3, started to plateau after day 3, and remained unchanged between days 4 and 14 of delay. This increase in capillary blood flow was mainly in the distal portion of the delayed skin flaps. There was no indication of an increase in the density of arteries in all delay periods studied. Our observations did not support the hypotheses that the delay phenomenon involves angiogenesis or long-term adaptation to ischemia, as have been hypothesized previously. The possible mechanism of delay is discussed.     

Peripheral neovascularization of muscle and musculocutaneous flaps in the pig.

Late loss of free muscle flaps following surgical or accidental trauma to the dominant vascular pedicle has been reported. In this study, time-dependent ligation of the dominant vascular pedicle was undertaken in denervated latissimus dorsi musculocutaneous or muscle-only island flaps in the pig. Muscle flaps were covered with a skin graft, and silicon rubber sheets were inserted between the flaps and their bases to simulate a poorly vascularized bed. Hemodynamic and viability studies were then performed using intravenous fluorescein (skin viability), tetrazolium blue (muscle viability), and radiolabeled 15-micron microspheres (capillary blood flow). Blood flow did not change in acutely raised musculocutaneous flaps (n = 10) but was significantly elevated in acutely raised muscle-only flaps (n = 10), suggesting that the skin paddle may steal blood flow from the underlying muscle in musculocutaneous flaps. Peripheral neovascularization at 1 day to 8 weeks was assessed (n = 30). Viability increased during the first week of revascularization and was not different in musculocutaneous and muscle-only flaps. Revascularization of muscle-only flaps was enhanced compared with musculocutaneous flaps in the 2- to 8-week period.     

Fasciocutaneous flaps: an experimental model in the pig

No experimental studies have substantiated the claim that fasciocutaneous flaps are superior to skin flaps. Using fasciocutaneous flaps designed in the pig, both flap survival and blood flow were assessed. The forelimb and hindlimb fasciocutaneous flaps survived to 8.2 +/- 0.3 cm and 7.9 +/- 0.3 cm, respectively, compared with 7.3 +/- 0.3 cm and 6.7 +/- 0.3 cm for the comparable cutaneous flaps, a statistically significant finding (p less than 0.01). Random fasciocutaneous flaps survive 12 to 18 percent longer than skin flaps. Using the radioactive microsphere technique, blood flow was measured after flap elevation, and flap survival was estimated using fluorescein. Again, a significant difference in flap survival was found, but there was no significant difference in measured blood flow. This can be explained by the relatively large interval between blood flow measurements (2 cm) compared with the observed difference in survival length (1.0 +/- 0.3 cm).     

Glucose metabolism in experimental skin flaps

The metabolism of glucose by rat abdominal skin flaps has been investigated at various times after flap elevation. Biopsies of flap skin taken during the first 3 days after flap elevation and incubated in vitro show a marked increase in glucose consumption and lactate production compared with normal skin. At the same time, flap tissue reserves of glucose and glycogen are lower than those of normal skin. Providing that some circulation persists, the magnitude of the changes in glucose metabolism is proportional to the degree of ischemia experienced by the flap tissue in vivo. In most cases, glucose consumption and lactate production return to normal by the end of the first week after flap elevation. These experiments thus further define a major ischemia-induced shift to anaerobic metabolism (glycolysis) that occurs in skin flaps.