Skin-flap metabolism in rats: oxygen consumption and lactate production

Overall glucose metabolism was evaluated by measuring the rate of oxygen consumption (QO2) and lactate production in the pedicle skin flaps of rats. Skin flaps exhibited increases in QO2 and lactate production in vitro. The distal portion of the flap is characterized by a greater deposition of glucose to lactate during the initial 3 days following flap elevation. The contribution of glycolysis and of the oxidative pathways to glucose metabolism in skin flaps approximates that in normal skin on day 7 postoperatively.     

Skin flap necrosis in guinea pigs: limitation of glucose supply and accumulation of lactate.

The distribution of glucose and lactate within skin flaps was determined in full-thickness guinea pig skin (excluding the panniculus carnosus). The distal end of the flaps had a low glucose content (less than 50 percent of normal) but high lactate level (2 to 3 times normal) during the 3 days after flap elevation. Progressively decreasing gradients of glucose content, and increasing gradients of lactate content, were demonstrated from the mid-region to the distal end of the flaps at 3 hours postoperatively. The decrease in glucose and the accumulation of lactate may play a significant role in skin necrosis.     

Early circulatory and metabolic events in island skin flaps of the pig

Circulatory and metabolic skin-flap events were studied prior to and up to 6 hours after elevation of buttock island flaps in pigs. During the elevation, significant reductions in superficial skin blood flow, measured by laser Doppler flowmetry (LDF) and dermal flap temperature, were seen. Significant correlations were found between blood flow and temperature. Total flap blood flow, measured as venous outflow, also showed an initial transient decrease, but 2 hours after flap construction, venous outflow had returned to preoperative values. A significant increase in lactate release, together with increased oxygen consumption and glucose uptake, was seen 4 hours after the surgical intervention. Hypoxanthine release, indicating ischemia, was seen only during the first hour after flap elevation. Noradrenaline outflow was noted after 4 and 6 hours, but there was no parallel reduction in flap blood flow. A great deal of the flow reduction in acutely elevated island flaps may thus be due to primary hypothermia rather than to the degenerative release of noradrenaline, which seems to have no early effect on skin flap blood flow. On the other hand, the noradrenaline release may be linked to an increased metabolic activity in the skin flaps.     

Metabolic adaptations in delayed skin flaps. Glucose utilization and hexokinase activity.

The distribution of glucose and hexokinase activity was determined in the epithelial tissue of delayed bipedicled skin flaps in guinea pigs. The periods of "delay" were 1, 3, 7, 14, or 21 days. The flap survival was maximal (100% of the flap) when the flap elevation was performed either 7 or 14 days following the "delay" procedure. When the flap elevation was performed 1, 3, or 21 days following the "delay" procedure, the result was partial necrosis. A differential distribution of epithelial glucose was found within the bipedicled flaps. The lowest glucose level (30% of normal) was at a distance of 2 to 3.5 cm from the end of the caudal pedicle during the first day after the "delay" procedure. This decreased glucose content recovered toward normal levels during the later part of the "delay" period. The bipedicled flaps exhibited increased hexokinase activity during the 3-week period of the "delay," and the responses of hexokinase activity and tissue glucose levels to the "delay" procedure were reciprocal in the caudal half of the flaps.     

Metabolism in pedicled and free TRAM flaps: a comparison using the microdialysis technique

The most common complication in flap surgery is of a circulatory nature. Impeded blood flow leads to altered metabolism in the tissue. Possible metabolic differences between different zones of the transverse rectus abdominis muscle (TRAM) flap were studied and the metabolism of pedicled and free TRAM flaps was compared intraoperatively and postoperatively. The method used was microdialysis, which is a useful technique for following local metabolic changes continuously in various tissues.Twenty-two patients with a pedicled or free TRAM flap were monitored using the microdialysis technique. Two microdialysis catheters were placed subcutaneously in the flap (zone I and zone II), and a third one was placed subcutaneously in the flank to serve as a control. The flaps were monitored intraoperatively and postoperatively for 3 days with repeated analyses of extracellular glucose, lactate, and glycerol concentrations. An additional analysis of pyruvate was performed in some patients to calculate the lactate-to-pyruvate ratio.This study showed that glucose, lactate, and glycerol change in a characteristic way when complete ischemia (i.e., complete inhibition of the blood circulation) is present. A slower stabilization with prolonged metabolic signs of ischemia, such as lower glucose and higher lactate and glycerol concentrations, was seen in zone II compared with zone I, and more pronounced metabolic signs of ischemia, but with a faster recovery, were detected in the free TRAM flap group than in the pedicled TRAM flap group. The fact that the metabolites returned to normal earlier in free flaps than in pedicled flaps may indicate that free TRAM flaps sustain less ischemic damage because of better and more vigorous perfusion.     

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.     

Enzymatic responses to skin flap elevation following a delay procedure

Alterations in enzyme activities of glucose metabolism were determined in the distal portion of the skin flaps of guinea pigs elevated following 3, 7, 14, or 21 days of the delay period. Hexokinase, pyruvate kinase, lactate dehydrogenase, and glucose 6-phosphate dehydrogenase activities were increased during the delay period, whereas isocitrate and malate dehydrogenases exhibited little alteration. Increases in glycolytic enzyme activities observed during the delay procedure were diminished in the flaps elevated during initial 3 days of the delay period, but were maintained or increased further in the flaps elevated at 7 to 21 days. Despite high levels of enzyme activities during the early period of the delay, the flaps elevated during this period exhibited partial necrosis with a low glucose level and decreased enzyme activities. It is concluded that tissue glucose level and its utilization are crucial factors for flap survival.     

Fuel metabolism in a pig myocutaneous island flap model

Unilateral denervated myocutaneous island flaps based on the superior epigastric vessels were raised in 24 pigs and the metabolic changes during the first 6 postoperative hours were monitored. Secondary to flap elevation, decreased arteriovenous (A-V) differences in oxygen, glucose, and alanine levels were observed, indicating the opening of A-V shunts and increased arterialization of the venous blood. Venous outflow increased during the first 3 hours, but the A-V differences in all metabolites were constant over the entire 6-hour observation period. Exchange of intermediary metabolites therefore increased within the first 3 hours, after which a steady state was established. The main flap fuels seemed to be fatty acids, muscle proteins, and glycogen, whereas blood-borne carbohydrates and ketone bodies played only a minor role as energy sources. Anaerobic metabolism was increased secondary to flap elevation from 2 to 6 percent as compared with preelevation values. No changes were found in concentrations of plasma catecholamines, which were constantly high. An average weight gain of 3 to 4 percent per hour was equally distributed to skin, subcutis, panniculus carnosus, and muscle. Thus the flap seemed to adapt to the new perfusion pattern within a few hours by a slightly increased anaerobic metabolism, but still with an oxidative metabolism of more than 90 percent.     

Vascular endothelial growth factor expression in pig latissimus dorsi myocutaneous flaps after ischemia reperfusion injury

Exogenous administration of vascular endothelial growth factor (VEGF) improves long-term viability of myocutaneous flaps. However, endogenous expression of this substance in flaps following ischemia-reperfusion injury has not been reported previously. Endogenous production of VEGF was measured in myocutaneous pig latissimus dorsi flaps after ischemia-reperfusion injury. Latissimus dorsi myocutaneous flaps (15 x 10 cm) were simultaneously elevated bilaterally in six Yorkshire-type male pigs (25 kg). Before elevation, three flap zones (5 x 10 cm) were marked according to their distance from the vascular pedicle. After isolation of the vascular pedicle, ischemia-reperfusion injury was induced in one flap by occlusion of the thoracodorsal artery and vein for 4 hours, followed by 2 hours of reperfusion. The contralateral flap served as a control. Perfusion in each zone was monitored by laser Doppler flowmetry at baseline, during ischemia, and during reperfusion. At the end of the protocol, skin and muscle biopsies of each flap zone and adjacent tissues were obtained for later determination of VEGF protein levels. VEGF concentrations were quantified using the Quantikine human VEGF immunoassay. Skin perfusion was similar among all flap zones before surgery. Flow fell in all flaps immediately after flap elevation. After 4 hours of ischemia, blood flow in the ischemic flaps was significantly decreased (p < 0.05) compared with nonischemic control flaps. After 2 hours of reperfusion, flow in ischemic flap skin recovered to levels similar to those in control flaps. VEGF protein concentrations in muscle tissue exceeded concentrations in skin and decreased from zones 2 to 3 in control and ischemic flaps. No significant differences in VEGF concentrations between ischemic and control muscle zones were observed. However, the concentration of VEGF in all muscle zones was significantly higher (p < 0.05) than muscle adjacent to the flap. Concentrations in skin zones 1 and 2 were significantly higher (p < 0.05) in ischemic flaps than in control flaps, but levels in zone 3 (most ischemic flaps) showed no significant difference.     

Comparative metabolic analysis of lactate for CHO cells in glucose and galactose

t-PA producing CHO cells have been shown to undergo a metabolic shift when the culture medium is supplemented with a mixture of glucose and galactose. This metabolic change is characterized by the reincorporation of lactate and its use as an additional carbon source. The aim of this work is to understand lactate metabolism. To do so, Chinese hamster ovary cells were grown in batch cultures in four different conditions consisting in different combinations of glucose and galactose. In experiments supplemented with glucose, only lactate production was observed. Cultures with glucose and galactose consumed glucose first and produced lactate at the same time, after glucose depletion galactose consumption began and lactate uptake was observed. Comparison of the metabolic state of cells with and without the shift by metabolic flux analysis show that the metabolic fluxes distribution changes mostly in the reactions involving pyruvate metabolism. When not enough pyruvate is being produced for cells to support their energy requirements, lactate dehydrogenase complex changes the direction of the reaction yielding pyruvate to feed the TCA cycle. The slow change from high fluxes during glucose consumption to low fluxes in galactose consumption generates intracellular conditions that allow the influx of lactate. Lactate consumption is possible in cell cultures supplemented with glucose and galactose due to the low rates at which galactose is consumed. Evidence suggests that an excessive production and accumulation of pyruvate during glucose consumption leads to lactate production and accumulation inside the cell. Other internal conditions such as a decrease in internal pH, forces the flow of lactate outside the cell. After metabolic shift the intracellular pool of pyruvate, lactate and H⁺ drops permitting the reversal of the monocarboxylate transporter direction, therefore leading to lactate uptake. Metabolic analysis comparing glucose and galactose consumption indicates that after metabolic shift not enough pyruvate is produced to supply energy metabolism and lactate is used for pyruvate synthesis. In addition, MFA indicates that most carbon consumed during low carbon flux is directed towards maintaining energy metabolism.     

Differential effects of venous stasis and arterial insufficiency on tissue oxygenation in myocutaneous island flaps: an experimental study in pigs.

The supply, consumption, and tissue tension of oxygen were studied in experimental bilateral myocutaneous island flaps in five control pigs and in eight pigs during progressive 1-hour intervals of flap ischemia. Progressive ischemia was obtained by partial to complete clamping of the artery in one flap, producing arterial insufficiency, and simultaneous clamping of the vein in the other flap, producing venous stasis. Blood flow was reduced to 50, 25, and 0 percent of baseline. In the arterial insufficiency flaps, the oxygen tension in subcutaneous tissue, muscle, and venous outflow was significantly reduced once blood flow was reduced to 50 percent of baseline. Oxygen consumption during partial vessel occlusion was lower in the venous stasis flaps than in the arterial insufficiency flaps when blood flow was reduced to 25 percent of baseline, suggesting either that cellular metabolism is reduced in the venous stasis flaps or that the oxygen which is delivered is unavailable for the cells. Increased presence of tissue fluid in the venous stasis flap inhibits the diffusion of oxygen through the interstitial tissue, and this may explain the lower oxygen consumption. During 3 hours of reperfusion, increased blood flow was observed in the arterial insufficiency flaps, whereas blood flow in the venous stasis flaps was sluggish. The arterial insufficiency flaps recovered more rapidly than the venous stasis flaps during the first hour of reperfusion, judged by the rate of increase in oxygen tension and the higher venous oxygen tension. Oxygen tension increased more rapidly in muscle than in subcutaneous tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Tissue oxygen measurements in delayed skin flaps: a reconsideration of the mechanisms of the delay phenomenon

The delay phenomenon was studied by measuring tissue oxygen tension (PsqO2) for 3 weeks in delayed flaps and normal adjacent contralateral skin in seven mongrel dogs. The PsqO2 fell after elevation of a bipedicle flap and rose again to normal by day 14. Delivery of oxygen to this flap was improved by surgical delay, so that when the bipedicle flap was reelevated on day 14 and its distal pedicle divided, minimal changes in PsqO2 occurred. When the control area was elevated on day 14 as a random-pattern flap, it had higher PsqO2 values than measured in the bipedicle flap on day 0, and therefore, it too had participated in the delay phenomenon, even though only its midline edge had been incised. An anatomic explanation for the findings was sought in wounds made in 10 rabbit ear chambers. After injury, blood flow was seen to be rerouted parallel to the incision line and was increased first by vasodilation and then also by angiogenesis until about day 14. Rerouting of blood by injury, inflammation, and angiogenesis due to repair appears to account for a significant portion of the delay phenomenon.     

Biomechanical and viscoelastic properties of skin,SMAS, and composite flaps as they pertain to rhytidectomy

Previous studies have focused on biomechanical and viscoelastic properties of the superficial musculoaponeurotic system (SMAS) flap and the skin flap lifted in traditional rhytidectomy procedures. The authors compared these two layers with the composite rhytidectomy flap to explain their clinical observations that the composite dissection allows greater tension and lateral pull to be placed on the facial and cervical flaps, with less long-term stress-relaxation and tissue creep. Eight fresh cadavers were dissected by elevating flaps on one side of the face and neck as skin and SMAS flaps and on the other side as a standard composite rhytidectomy flap. The tissue samples were tested for breaking strength, tissue tearing force, stress-relaxation, and tissue creep. For breaking strength, uniform samples were pulled at a rate of 1 inch per minute, and the stress required to rupture the tissues was measured. Tissue tearing force was measured by attaching a 3-0 suture to the tissues and pulling at the same rate as that used for breaking strength. The force required to tear the suture out of the tissues was then measured. Stress-relaxation was assessed by tensing the uniformly sized strips of tissue to 80 percent of their breaking strength, and the amount of tissue relaxation was measured at 1-minute intervals for a total of 5 minutes. This measurement is expressed as the percentage of tissue relaxation per minute. Tissue creep was assessed by using a 3-0 suture and calibrated pressure gauge attached to the facial flaps. The constant tension applied to the flaps was 80 percent of the tissue tearing force. The distance crept was measured in millimeters after 2 and 3 minutes of constant tension. Breaking strength measurements demonstrated significantly greater breaking strength of skin and composite flaps as compared with SMAS flaps (p < 0.05). No significant difference was noted between skin and composite flaps. However, tissue tearing force demonstrated that the composite flaps were able to withstand a significantly greater force as compared with both skin and SMAS flaps (p < 0.05). Stress-relaxation analysis revealed the skin flaps to have the highest degree of stress-relaxation over each of five 1-minute intervals. In contrast, the SMAS and composite flaps demonstrated a significantly lower degree of stress-relaxation over the five 1-minute intervals (p < 0.05). There was no difference noted between the SMAS flaps and composite flaps with regard to stress-relaxation. Tissue creep correlated with the stress-relaxation data. The skin flaps demonstrated the greatest degree of tissue creep, which was significantly greater than that noted for the SMAS flaps or composite flaps (p < 0.05). Comparison of facial flaps with cervical flaps revealed that cervical skin, SMAS, and composite flaps tolerated significantly greater tissue tearing forces and demonstrated significantly greater tissue creep as compared with facial skin, SMAS, and composite flaps (p < 0.05). These biomechanical studies on facial and cervical rhytidectomy flaps indicate that the skin and composite flaps are substantially stronger than the SMAS flap, allowing significantly greater tension to be applied for repositioning of the flap and surrounding subcutaneous tissues. The authors confirmed that the SMAS layer exhibits significantly less stress-relaxation and creep as compared with the skin flap, a property that has led aesthetic surgeons to incorporate the SMAS into the face lift procedure. On the basis of the authors' findings in this study, it seems that that composite flap, although composed of both the skin and SMAS, acquires the viscoelastic properties of the SMAS layer, demonstrating significantly less stress-relaxation and tissue creep as compared with the skin flap. This finding may play a role in maintaining long-term results after rhytidectomy. In addition, it is noteworthy that the cervical flaps, despite their increased strength, demonstrate significantly greater tissue creep as compared with facial flaps, suggesting earlier relaxation of the neck as compared with the face after rhytidectomy.     

Nuclear magnetic resonance spectroscopy of skin: predictive correlates for clinical application

The first application of phosphorous 31 (31P) and proton (1H) nuclear magnetic resonance (NMR) spectroscopy to the analysis of the metabolic profiles of skin flaps in a rat model and of human skin grafts is presented. Resonances of adenosine triphosphate (ATP), phosphocreatine (PCr), and inorganic phosphate (Pi) were identified in 31P nuclear magnetic resonance spectra. Resonances of phosphocreatine, creatine (Cr), and lactate (Lac) were identified in 1H nuclear magnetic resonance spectra. The most significant finding was the substantial presence of phosphocreatine as the major high-energy phosphometabolite in mammalian skin, a finding which heretofore has not been widely recognized. An energy shuttle between phosphocreatine and ATP is operative in skin to buffer the fall in ATP during ischemic (anaerobic) insult. Inability to replenish exhausted phosphocreatine reserves predictively correlates with eventual flap necrosis. We have defined and analyzed temporal fluxes in the phosphocreatine-creatine and phosphocreatine plus creatine-lactate ratios by proton nuclear magnetic resonance. Both are sensitive, accurate, and unambiguous early prognostic indices of eventual flap outcome. These findings support the concept that the fate of a flap may be established as early as 3 hours after elevation and have laid the groundwork for development and application of noninvasive in vivo nuclear magnetic resonance spectroscopy to the study of skin flaps in animals and humans.     

Increase in skin-flap survival by the vasoactive drug buflomedil

The effect of buflomedil to protect skin tissue from ischemia and necrosis was studied in random cutaneous flaps. Measurements were performed by intravital microscopy on the microcirculatory level of capillary perfusion in a flap model in the hairless mouse. In 30 hairless mice, single-pedicle flaps measuring 6 x 16 mm were raised perpendicular to the spine of the animal. This flap develops a reliable amount of necrosis at its distal edge over a period of 7 days. A group of 10 mice received intravenous injections of buflomedil in doses of 3 mg/kg per day diluted in 0.1 ml normal saline beginning 4 hours before flap elevation and for 6 consecutive days postoperatively. In addition, 10 further animals received the same treatment except that it was started 5 minutes after flap elevation. In 10 mice serving as controls, normal saline in equal volumes as in the experimental groups was applied. By means of intravital microscopy, functional vessel density (FVD) was determined in 2.5-mm increments from the flap's base to its distal edge at 1, 6, and 24 hours after elevation. Skin-flap survival was quantified by measuring the necrotic area on day 7 by means of digital planimetry. Functional vessel density was preserved in the distal flap of animals pretreated with buflomedil, revealing a higher functional vessel density at 10.0 mm (p less than 0.01), 12.5 mm (p less than 0.05), and 15.0 mm (p less than 0.001) from the flap's base as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of the isolated perfused rat hindquarter for the study of muscle metabolism

1. The metabolic integrity of a new isolated rat hindquarter preparation was studied. The hindquarter was perfused with a semi-synthetic medium containing aged human erythrocytes. More than 95% of the oxidative metabolism of the preparation was due to muscle, the remainder being due to bone, adipose tissue and, where present, skin. 2. Consumption of O(2), glucose utilization, glycerol release and lactate production were similar in the presence and in the absence of the skin, indicating that the latter contributed little to the overall metabolism of the preparation. 3. After 40min of perfusion, tissue concentrations of creatine phosphate, ATP and ADP were similar to those found in muscle taken directly from intact animals. The muscle also appeared normal under the electron microscope. 4. The hindquarter did not lose K(+) to the medium during a 30min perfusion. In the presence of insulin it had a net K(+) uptake. 5. Insulin caused a sixfold increase in glucose uptake, stimulated O(2) consumption by nearly 40% and depressed glycerol release to less than half the control value. 6. Bilateral sciatic-nerve stimulation caused severalfold increases in O(2) consumption and lactate production. In the absence of insulin nerve stimulation also enhanced glucose uptake; in the presence of insulin it did not further increase the already high rate of glucose uptake. 7. Rates of lactate production and O(2) consumption of the rat hindquarter in vivo and the isolated perfused hindquarter were very similar. 8. Ketone bodies were a major oxidative fuel in vivo of the hindquarter of a rat starved for 2 days. If the acetoacetate and 3-hydroxybutyrate removed by the tissue were completely oxidized, they would have accounted for 77% of the O(2) consumption. 9. Acetoacetate accounted for 84% of the ketone bodies removed by the hindquarter in vivo even though its arterial concentration was half that of 3-hydroxybutyrate. 10. Similar rates of acetoacetate and 3-hydroxybutyrate utilization were observed in the perfused hindquarter. 11. Acetoacetate utilization by the perfused hindquarter was not diminished by the addition of either oleate or insulin to the perfusate. 12. Oxidation of glucose to CO(2) accounted for less than 4% of the O(2) consumed by the perfused hindquarter in both the presence and the absence of insulin. 13. The results indicate that the isolated perfused hindquarter is a useful tool for studying muscle metabolism. They also suggest that ketone bodies, if present in sufficient concentration, are the preferred oxidative fuel of resting muscle.     

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.     

Tissue carbon dioxide tension: a putative specific indicator of ischemia in porcine latissimus dorsi flaps

Free flap surgical procedures are technically challenging, and anastomosis failure may lead to arterial or venous occlusion and flap necrosis. To improve myocutaneous flap survival rates, more reliable methods to detect ischemia are needed. On the basis of theoretical considerations, carbon dioxide tension, reflecting intracellular acidosis, may be suitable indicators of early ischemia. It was hypothesized that tissue carbon dioxide tension increased rapidly when metabolism became anaerobic and would be correlated with acute venoarterial differences in lactate levels, potassium levels, and acid-base parameters. Because metabolic disturbances have been observed to be less pronounced in flaps with venous occlusion, it was hypothesized that tissue carbon dioxide tension and venoarterial differences in lactate and potassium levels and acid-base parameters would increase less during venous occlusion than during arterial occlusion. In 14 pigs, latissimus dorsi myocutaneous flaps were surgically isolated, exposed to acute ischemia for 150 minutes with complete arterial occlusion (seven subjects) or venous occlusion (seven subjects), and reperfused for 30 minutes. After arterial occlusion, pedicle blood flow decreased immediately to less than 10 percent of baseline flow. Blood flow decreased more slowly after venous occlusion but within 3 minutes reached almost the same low levels as observed during arterial occlusion. Venous oxygen saturation decreased from approximately 70 percent to approximately 20 percent, whereas oxygen uptake was almost arrested. Tissue carbon dioxide tension increased to two times baseline values in both groups (p < 0.01). The venoarterial differences in carbon dioxide tension, pH, base excess, glucose levels, lactate levels, and potassium levels increased significantly (p < 0.01). Tissue carbon dioxide tension measured during the occlusion period were closely correlated with venoarterial differences in pH, base excess, glucose levels, lactate levels, and potassium levels (median r2, 0.67 to 0.92). After termination of arterial or venous occlusion, more pronounced hyperemia was observed in the arterial occlusion group than in the venous occlusion group (p < 0.05). Oxygen uptake (p < 0.05) and venoarterial differences in lactate and potassium levels (p < 0.05) were significantly more pronounced in the arterial occlusion group. In the venous occlusion group, with less pronounced hyperemia, venoarterial differences in acid-base parameters remained significantly different from baseline values before occlusion (p < 0.01). The data indicate that tissue carbon dioxide tension can be used to detect anaerobic metabolism, caused by arterial or venous occlusion, in myocutaneous flaps. The correlations between carbon dioxide tension and venoarterial differences in acid-base parameters were excellent. Because carbon dioxide tension can be measured continuously in real time, such measurements are more likely to represent a clinically useful parameter than are venoarterial differences.     

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).