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Our aim was to find out whether thrombosis has a key role in distally ischaemic flaps and whether heparin improves flap survival in distally ischaemic myocutaneous and pure skin flaps in pigs. In experiment 1 we measured the concentration of coagulation factors in the venous effluent from both viable flaps and distally ischaemic flaps. In experiment 2 radioactively labelled blood components (red cells, platelets and fibrinogen) were injected intravenously and the distribution of each tracer was measured. In experiment 3 either heparin or saline was given as a local, continuous direct intra-arterial infusion. Fluorescein was used in all experiments to estimate the eventual flap survival. Our results indicate that thrombosis is not an important factor in distal ischaemia, and that heparin did not improve survival. Instead, there seems to be selective pooling of formed elements in the ischaemic portion of the flap.

Ischemia-reperfusion injury is one of the major problems in reconstructive microsurgery. The ischemic insult may be due to an occlusion of either the artery or the vein. Clinical observations have suggested that flap survival is more sensitive to venous stasis than to arterial ischemia. The current study evaluated the viability of the myocutaneous rectus abdominis flap following secondary arterial or venous occlusion and its possible dependency on tissue metabolites and length of the preceding reperfusion period. Forty-eight bilateral 5 X 10 cm myocutaneous rectus abdominis flaps were elevated in 24 pigs and exposed to consecutive periods of primary ischemia (2 hours), reperfusion (1, 4, 8, and 12 hours), and secondary pedicle occlusion (6, 8, 10, 12, 14, or 16 hours) of arterial or venous origin. Muscle adenosine triphosphate (ATP) and glucose-6-phosphate (G6P) were assessed immediately after flap elevation, at the end of primary ischemia, after reperfusion, and at the end of secondary ischemia. Flap viability was assessed 5 days after the operation. Secondary venous occlusion resulted in reduced survival rates as compared with arterial occlusion (9 of 24 versus 20 of 24; p < 0.01), although the average ATP content was higher in flaps subjected to venous stasis [median (25 to 75) percentiles, 3.7 (1.7 to 7.1) micromol/gm protein] than in those subjected to arterial ischemia 1.2 (0.8 to 1.8 micromol/gm protein) (p < 0.01). During reperfusion, muscle ATP decreased from 28.5 (17.9 to 36.6) micromol/gm protein to 15.4 (7.4 to 24.9) micromol/gm protein (p < 0.01) and glucose-6-phosphate from 7.6 (4.1 to 11.6) micromol/gm protein to 1.0 (0.5 to 4.1) micromol/gm protein (p < 0.01). Still, flap survival following secondary arterial ischemia was improved by increasing the reperfusion time from 1 to 8 hours (p < 0.05). No effect of reperfusion time was seen on viability after venous stasis. In conclusion, despite poorer flap survival, venous stasis was less detrimental to tissue ATP level, suggesting that the continued inflow may have supplied substrates for glycolysis. Furthermore, the larger blood volume may have accumulated the glycolytic waste products. After reperfusion, the recovery of aerobic metabolism was far from complete, and cellular glycolytic substrates were nearly exhausted. However, prolongation of the reperfusion time preceding secondary arterial ischemia improved flap survival.

In this study, simulated "poor" repairs applied to transverse incisions in the iliac arteries of 40 rats were the basis for comparing the effect of variations in blood flow on thromboembolism. Using vital microscopy and digital image processing, we performed 2 experiments. In the first experiment (n = 20), the reduction of post-repair blood flow by approximately 50% resulted in an 83% reduction in the total number of emboli appearing in the microcirculation of the cremaster muscle distal to the repair. In the second experiment (n = 20), the same reduction in blood flow typically resulted in larger repair-site thrombi which required significantly more time to grow to their maximum size. We conclude that reducing pedicle artery blood flow to approximately half in our rat model during reperfusion can protect the downstream microcirculation from embolic injury without increasing the incidence of thrombotic occlusion.

It has been suggested by clinical observations that acute venous thrombosis following free-flap surgery results in more severe tissue injury than postoperative arterial thrombosis. This current study, in the pig model, was designed (1) to determine the rate of survival and the percentage area of flap survival in both cutaneous and myocutaneous flaps following a secondary venous ischemic insult, (2) to compare this with findings following a secondary arterial ischemic insult, and (3) to determine the reliability of laser Doppler flowmetry and dermofluorometry index in the prediction of necrosis outcome following both venous and arterial ischemic insults. A total of 116 flaps were elevated in 29 pigs. Data analysis documented a decrease in the rate of flaps surviving venous ischemia as compared with arterial ischemia or control and of arterial ischemia as compared with control. In contrast to our previous work, a lower rate of buttock flaps survived a secondary ischemic insult (of either arterial or venous etiology) than did the cutaneous component of the myocutaneous flaps. As expected, as the length of ischemia increased, the rate of flaps surviving decreased, as did the percentage area of survival. Although laser Doppler performed slightly better than dermofluorometry index, as measured on immediate reperfusion following secondary venous ischemia, both were relatively poor predictors of eventual survival or necrosis. Under conditions of immediate reperfusion following secondary arterial ischemia, dermofluorometry index proved to be a superior predictor of ultimate necrosis as compared with laser Doppler flowmetry.

Although endothelial cell injury and microcirculatory intravascular thrombosis have been implicated in the pathophysiology of skin-flap failure, the basic underlying pathophysiology has not been documented previously. This study focuses on the morphologic changes and the alteration in platelet, fibrinogen, antithrombin III, and von Willebrand factor levels in flaps injured by arterial ischemia and reperfusion. A thrombogenic arterial anastomosis model is compared with simple arterial clamping as methods to achieve flap ischemia. Bilateral buttock skin flaps and latissimus dorsi island flaps were elevated in 12 pigs. All flaps had a primary ischemic insult of 2 hours' duration by simple clamp application. During this interval, a thrombus-generating, microvascular anastomosis was prepared, and during a 2-hour period of reperfusion, laser Doppler and transiluminator monitoring of the vascular pedicle allowed documentation of embolic events from the thrombus-generating anastomosis. In group 1 (n = 6), the flaps were then subjected to 7 (buttock skin) and 5 (latissimus dorsi) hours of complete arterial ischemia by clamping. During the secondary ischemic period, the poor microanastomosis was resected and repaired. Radioactively labeled autologous platelets (111In) and human fibrinogen (125I) were injected intravenously half an hour before secondary reperfusion. After 4 hours of reperfusion, flap biopsies and venous effluent were collected and prepared for electron microscopic analysis. The flaps and control tissue were harvested and the radioactivity was counted. In group 2 (n = 6), flaps were subjected to 6 hours of secondary ischemia by using the same technique as in group 1. Central venous and flap venous blood was sampled at baseline as well as upon immediate secondary reperfusion and after 4 and 8 hours of reperfusion. The hematocrit, platelet count, fibrinogen, antithrombin III, and von Willebrand factor levels were determined for these intervals. Platelets and fibrinogen accumulated significantly in buttock skin flaps and in the latissimus dorsi skin and muscle components as compared with similar control tissue (p < 0.05). There was no significant difference in platelet or fibrinogen accumulation after comparing the two ischemic models. Electron microscopic studies showed occluded capillaries with activated platelets in the flaps. Control tissue showed very little capillary occlusion. Platelet count was significantly decreased both in central venous (p < 0.05) and in adventitial infolding flap venous blood (p < 0.025) during immediate reperfusion as compared with baseline. These findings confirm that microcirculatory intravascular thrombosis is implicated in skin-flap ischemia-reperfusion injury. This study provides physiologic support for treatment modalities aimed at counteracting the various components in the coagulation pathways responsible for thrombus formation.

Although endothelial cell injury and microcirculatory intravascular clotting have been implicated in the pathophysiology of skin-flap failure and various hematologically active drugs have been used to improve flap survival, the basic underlying pathophysiology has not been documented previously. In this study of venous ischemia in pig flaps, we focus on the accumulation and distribution of platelets and fibrinogen in the flap, on the morphologic changes in the flap microcirculation, and on changes in various coagulation factors in the venous effluent from the flap. Bilateral buttock skin flaps and latissimus dorsi myocutaneous flaps were designed and elevated on 12 pigs. All flaps had a primary ischemic insult (clamp application to the vascular pedicle) of 2 hours, followed by 2 hours of reperfusion, and then one side was subjected to a 6-hour period of secondary venous ischemia (clamp application to the dominant flap vein). In six animals, radioactively labeled autologous platelets and human fibrinogen were injected intravenously half an hour before termination of secondary venous ischemia. Flaps were weighed and counted for radioactivity. Flap biopsies and the buffy coat of venous effluent were processed for electron microscopy. In the other six animals, venous effluent was collected before secondary ischemia, upon immediate reperfusion, and at 4 and 8 hours after termination of secondary ischemia. Venous plasma levels of fibrinogen, von Willebrand factor, and antithrombin III were measured. Platelet and fibrinogen accumulation was increased in flaps with venous stasis when compared with control flaps at both time intervals studied; a twofold increase was seen prior to reperfusion, and a threefold increase was seen following 4 hours of reperfusion. Venous effluent could not be collected from buttock skin flaps because of slow reflow and clotting in the collecting system. In comparing the venous effluent of control flaps with that of venous ischemic latissimus dorsi flaps, hematocrit was significantly elevated. Blood samples collected for analysis of fibrinogen, antithrombin III, and von Willebrand factor could not be analyzed because of postcollection clotting. Electron microscopy showed extravasation of red blood cells and activated platelets, fibrin, and red blood cells in distended and partly disrupted capillaries. The venous ischemia reperfusion injury is associated with thrombosis in the microcirculation and alterations in consumption of coagulation factors. This study gives physiologic support for potential beneficial effects of treatment modalities that aim at counteracting the different components of thrombus formation.

To further clarify the pathogenesis of the poorer prognosis in skin flaps exposed to venous stasis compared with arterial insufficiency, a microsphere study was conducted in bilateral rectus abdominis island flaps in seven pigs. The relationship between capillary blood flow and arteriovenous (A-V) shunting was studied during progressive 1-hour intervals of arterial insufficiency and venous stasis and during 3 hours of reperfusion. Under controlled conditions, total blood flow was reduced from 100 percent to both 50 and 25 percent by application of an adjustable clamp on the artery supplying one flap and on the vein draining the contralateral flap. The relative distribution between A-V shunt flow and capillary blood flow was different in arterial insufficiency when compared with venous stasis at both the 50 percent and the 25 percent blood flow levels. In the arterial insufficiency flaps, the A-V shunt flow and capillary blood flow shared the total blood flow in the following percentages: 64/36 (at 100 percent total blood flow), 44/56 (at 50 percent total blood flow level), and 22/78 (at 25 percent total blood flow level). In the venous stasis flaps, the A-V shunt flow and the capillary blood flow shared the total blood flow in percentages of 70/30, 66/34, and 55/45, respectively. Hence, in arterial insufficiency flaps, capillary blood flow was spared by a relatively greater decline in A-V shunting compared with venous stasis flaps. Redistribution of capillary blood flow from subcutaneous tissue to muscle was observed, whereas blood flow was equally distributed throughout the length of the flaps at all flow levels.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

In order to further improve the understanding of hemodynamic changes in the immediate postoperative phase after elevation of myocutaneous flaps, regional blood flow and arteriovenous (A-V) shunting were measured in rectus abdominis island flaps in 8 pigs. Radioactive microspheres of two sizes (15 and 50 micron) were used. Approximately half (53.4 +/- 6 percent) of the 15-micron microspheres and one-fourth (24.1 +/- 6 percent) of the 50-micron microspheres entering the flap appeared in the venous outflow. Compared with the control area, A-V shunting was significantly increased in muscle and substantially more pronounced in skin. Nutritional blood flow, total blood flow, and vascular volume were increased in muscle and unchanged in skin and subcutis. The lowest tissue hematocrit of 7 +/- 1 percent was found in skin as compared with a central hematocrit of 35 +/- 2 percent. Tissue hematocrit in flap muscle was decreased to 17 +/- 2 percent when compared with control muscle (22 +/- 3 percent), and the mean transit time for blood was correspondingly decreased. Thus vasodilation provided increased perfusion through muscular capillaries and through A-V shunts. Shunting of 15-micron microspheres appeared to take place not only in skin, but also in subcutis and muscle, which challenges the widespread belief that A-V shunting does not occur in muscle.

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.

The relationship between tissue oxygen tension (PO2) and blood flow, blood gas tensions, oxygen delivery, and oxygen consumption was investigated in myocutaneous island flaps in 24 pigs. The tissue PO2 was measured by the silicone rubber tonometer technique. Capillary blood flow was increased during the first 3-4 hours after implantation of tonometers and they must, therefore, be implanted 3-4 hours before use. After raising the flap, mean (SEM) total flap blood flow increased from 11.2 (0.8) ml/min to 16.0 (1.3) ml/min within the first three hours. Mean (SEM) subcutaneous tissue PO2 decreased from 9.5 (0.6) kPa to 5.2 (0.7) kPa over six hours after the procedure, whereas muscle PO2, blood oxygen tension, and arteriovenous oxygen difference were unchanged. Hence, both the supply to, and use of oxygen in, the flap increased. Muscular and subcutaneous oxygen tensions were about 3 and 1 kPa, respectively, lower than venous oxygen tension. Tissue PO2 did not correlate with blood flow, blood oxygen tensions, arteriovenous differences in oxygen tension, or with oxygen supply in a cross section of animals. Tissue PO2 seems to reflect accurately the balance between oxygen supply and consumption, which might be the most useful indicator for continuous flap monitoring.

In eight pigs, total blood flow, regional capillary blood flow distribution, and arteriovenous (AV) shunting were studied during the first 4 postoperative hours after elevation of a myocutaneous rectus abdominis island flap. Capillary blood flow and AV shunting were measured using radioactive microspheres before flap creation and 1 and 4 hours after surgery. Total blood flow, measured continuously as venous outflow, increased in the first postoperative hour (p less than 0.05). Elevation of the flap caused a slight decrease in skin capillary blood flow (p less than 0.05), whereas muscular capillary blood flow increased (p less than 0.01). AV shunting accounted for 50 percent of the total flap blood flow, whereas it was negligible in the abdominal wall prior to flap elevation. Thus stalk blood flow, skin appearance, and skin temperature may be poor indicators of nutritional capillary perfusion. However, the clinical and nutritional consequences of these findings remain to be established.

The effect of increased and decreased uniaxial tissue tension on capillary blood flow, plasma volume, edema formation, and vascular permeability in myocutaneous flaps was studied. A total of 64 equally sized arterialized myocutaneous flaps were outlined on the abdomen of 16 dogs. The four areas on each dog were randomized to either untouched control area, reattachment to normal tension, increased (one and one-half times the original length), or decreased (one-half times the original length). Capillary blood flow measured by the radioactive microsphere technique two hours after operation was decreased in the muscular part of flaps reattached at decreased and normal tension (p less than 0.05). The muscular blood flow was unchanged when flaps were reattached at increased tension and significantly higher than in flaps reattached at decreased tension (p less than 0.05). No differences were found in skin or subcutaneous blood flow. There were no differences in plasma volume, vascular permeability, or total water content between flaps attached under different tensions, whereas the plasma volume was increased in muscle in all three flap types (p less than 0.05) presumably secondary to venous stasis. The study implies that the decreased capillary blood flow seen in the muscular component of a myocutaneous flap in the immediate postoperative period may be counteracted by a somewhat increased reattachment tension.

In pigs, latissimus dorsi musculocutaneous island flaps and buttock skin island flaps were raised. Subcutaneous (PscO2) and intramuscular oxygen tension (PimO2) were measured using a non-heated needle electrode before, during and after repeated occlusion of the supplying artery or the draining vein. During arterial and venous occlusion, the tissue oxygen tension in the musculocutaneous flap dropped rapidly. A plateau was reached after 15 min. After arterial occlusion the mean value was 20 mmHg (SEM = +/- 5 mmHg, N = 6) in the subcutis and 16 mmHg in the muscle (SEM = +/- 4 mmHg, N = 10). After venous occlusion the mean value was 11 mmHg (SEM = +/- 3 mmHg, N = 6) in the subcutis. In the skin flap the drop of PscO2 was slower, and after 30 min of arterial occlusion the mean value was 29 mmHg (SEM = +/- 9 mmHg, N = 6). This study has shown that tissue oxygen tension measurement can be used as a sensitive indicator of acute impairment of the supplying vessels in island flaps. The method seems to have potential for monitoring free tissue transfers. A comparable decrease in PscO2 was found for arterial and venous impairment.

We investigated the effect of progressive normovolemic hemodilution with Dextran 70 on subcutaneous tissue oxygen tension (PscO2) in canine random pattern flaps and in adjacent intact skin. PscO2 was measured polarographically in implanted oxygen-permeable Silastic catheters. The mean PscO2 of 5.7 kPa in intact subcutis at hematocrit (HCT) 40 was maintained or insignificantly improved during hemodilution to a HCT of 14. The mean flap PscO2 of 3.1 kPa at HCT 40 was maintained down to HCT 20. Most flap measuring sites exhibited a PscO2 improvement in an individual HCT range at some point during hemodilution. The increment in PscO2 tended to be relatively greater and to occur at lower Hct values in locations with more severe ischemia initially. Central hemodynamics were characterized by a lowered total peripheral resistance and an increased cardiac output, whereas systemic and pulmonary arterial blood pressures and central venous pressure remained essentially unchanged.