Fluorometric analysis of an attempt to reclaim ischemic flaps in rats with Fluosol

An experiment was designed to answer two questions as they apply to random skin-flap survival: Is there a therapy that can improve random skin-flap survival when given postoperatively? And if so, when does one start such a therapy? Fluosol-DA 20% (Fluosol) has increased random skin-flap survival when given preoperatively in our laboratory. An experiment was devised to see if it could rescue failing flaps. One-hundred Sprague-Dawley rats were divided into a control (N = 25) and five experimental groups (N = 15). All had 10 X 13 cm reverse McFarlane random flaps raised and reinset. The experimental groups underwent hemodilution with either Ringer's lactate or Fluosol at 4, 8, and 12 hours after flap elevation. All were kept in 50% oxygen for 72 hours postoperatively. The flaps and their corresponding necrotic areas were measured on day 7. As to when to institute a therapy, we simultaneously evaluated the use of a microfluorometer as a monitor of flap survival. Analysis of flap survival showed little difference between control and experimental Ringer's lactate or Fluosol groups. Analysis of the microfluorometric data led to the following points. First, as a monitor of flap viability, it is limited by a lack of specificity and sensitivity. Second, comparison of the data from portions of the flap destined to live with those destined to die suggests that it may not be failure of circulatory inflow that leads to flap death.     

Effect of hyperbaric oxygen and medicinal leeching on survival of axial skin flaps subjected to total venous occlusion

This study evaluates the effect of hyperbaric oxygen and medicinal leeching on axial skin flaps subjected to total venous occlusion. Axial epigastric skin flaps (3 x 6 cm) were elevated on their vascular pedicles in 40 male Wistar rats. Total venous occlusion was achieved by division of all veins draining the skin flap. Arterial inflow was left intact. Animals were randomly assigned to one of five groups: sham (n = 8); control, total venous occlusion only (n = 8); occlusion with hyperbaric oxygen (n = 8); occlusion with leeching (n = 8); occlusion with leeching and hyperbaric oxygen (n = 8). The hyperbaric oxygen protocol consisted of 90-minute treatments, twice daily, with 100% O2 at 2.5 atmospheres absolute for 4 days. The leeching protocol consisted of placing medicinal leeches on the congested flaps for 15 minutes, once daily, for 4 days. Laser Doppler measurements of flap perfusion were recorded preoperatively, postoperatively, and on postoperative days 1 and 3. The percentage of flap necrosis was evaluated on postoperative day 3. Mean percentage necrosis and mean laser Doppler readings were compared between both groups. The flaps in the sham group demonstrated 99 percent survival, whereas the flaps in the occlusion-only group demonstrated 100 percent necrosis. The flaps in the occlusion with oxygen, the occlusion with leeching, and the occlusion with oxygen and leeching groups demonstrated 1, 25, and 67 percent survival, respectively. Sham laser Doppler readings remained within normal limits. Laser Doppler readings in the occlusion-only and the occlusion with oxygen groups decreased to negligible levels on postoperative day 1, and on postoperative day 3 no perfusion was demonstrated. In both the occlusion with leeching and the occlusion with leeching and oxygen groups, there was also a significant decrease in laser Doppler measurements after surgery, but perfusion remained stable throughout the remainder of the study. This study demonstrates that hyperbaric oxygen alone is not an effective treatment for skin flaps compromised by total venous occlusion. The combination of leeching and hyperbaric oxygen treatment of total venous occlusion results in a significant increase in flap survival above that found with leeching alone. It appears that hyperbaric oxygen is effective because of the venous outflow provided by leeching as demonstrated by laser Doppler flow readings.     

Comparison of three different supercharging procedures in a rat skin flap model

A significant clinical problem in reconstructive surgery is partial loss of a pedicled flap. To resolve this problem, various methods of vascular augmentation have been developed; "supercharging" is one of those techniques. A new rat flap model was developed for investigation of the supercharging procedure, and the efficacy of the arterial supercharging method was examined. The purpose of this study was to investigate how an arterial supercharging procedure could generate large flap survival areas with different supercharging positions in rats. On the basis of the vascular anatomical features of rats, a circumferential skin flap from the lower abdomen to the back, measuring 4 x 12 cm, was marked. The flap was divided along the dorsal midline. Forty rats were divided into four experimental groups, as follows: group 1 (control), flaps based only on the deep circumflex iliac artery and vein; group 2, flaps supercharged with the ipsilateral superficial inferior epigastric artery; group 3, flaps supercharged with the contralateral superficial inferior epigastric artery; group 4, flaps supercharged with the contralateral deep circumflex iliac artery. On the fourth postoperative day, the flaps were evaluated with measurements of necrosis and survival areas. Microfil (Flow Tech, Inc., Carver, Mass.) was then injected manually throughout the body, and the vascular changes produced by supercharging were angiographically evaluated. Compared with group 1 (control), the flap survival areas were significantly greater in distally supercharged flaps in groups 3 and 4 (mean flap survival, 91.2 +/- 5.2 percent and 90.5 +/- 10.6 percent, respectively; p < 0.001) and in proximally supercharged flaps in group 2 (45.9 +/- 4.1 percent, p < 0.05). Angiographic assessment of the flaps that survived completely revealed marked dilation of the choke veins among the territories and reorientation of dilated veins along the axes of the flaps. This study suggests that distal arterial supercharging (contralateral superficial inferior epigastric artery or contralateral deep circumflex iliac artery) is more effective than proximal arterial supercharging (ipsilateral superficial inferior epigastric artery) in increasing flap survival. Although the rat skin flap may not be analogous to human flaps, distal arterial supercharging might have useful therapeutic potential in increasing flap survival in clinical practice.     

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.     

Effects of external beam irradiation on the TRAM flap: an experimental model

The rat model of the transverse rectus abdominis musculocutaneous (TRAM) flap was used in the present study to determine the effects of external beam radiation on myocutaneous flap histology and pathophysiology. A total of 57 adult Sprague-Dawley rats underwent a TRAM procedure. A pilot study with 17 animals was first performed to determine proper radiation dosages, and the remaining 40 rats were then used in the definitive study. In half of the definitive study group, the flaps were subjected to fractionated doses of external beam radiation, whereas the other half served as controls. Six weeks after the last radiation dose, all animals were killed and the flaps were harvested for mechanical assessment and histopathologic evaluation. All TRAM flaps survived in both groups. The irradiated and nonirradiated flaps were minimally distinguishable in viscoelastic properties, as well as by histopathologic examination. Growth of the flap in the irradiated animals was significantly diminished (48 percent average surface area increase in irradiated flaps, versus 92 percent increase in nonirradiated flaps, p < 0.05). These findings suggest that the myocutaneous flap is relatively resistant to some of the known adverse affects of radiation on living tissues.     

Pharmacologic enhancement of rat skin flap survival with topical oleic acid

This study was instituted to investigate in a rat model the effect of topical coadministration of the penetration enhancer oleic acid (10% by volume) and RIMSO-50 (medical grade dimethyl sulfoxide, 50% by volume) on rat skin flap survival. A rectangular abdominal skin flap (2.5 x 3 cm) was surgically elevated over the left abdomen in 40 nude rats. The vein of the flap's neurovascular pedicle was occluded by placement of a microvascular clip, and the flap was resutured with 4-0 Prolene to its adjacent skin. At the end of 8 hours, the distal edge of the flap was reincised to gain access to the clips and the clips were removed. After resuturing of the flap's distal edge to its adjacent skin, the 40 flaps were randomly divided into four groups. Group 1 (control) flaps were treated with 5 g of saline, group 2 (dimethyl sulfoxide) flaps were treated with 2.7 g of dimethyl sulfoxide (50% by volume), group 3 flaps (oleic acid) were topically treated with 0.45 g of oleic acid (10% by volume), and group 4 (dimethyl sulfoxide plus oleic acid) flaps were treated with a mixture of 0.45 g of oleic acid (10% by volume) and 2.7 g of dimethyl sulfoxide (50% by volume) diluted in saline. Each flap was topically treated with 5 ml of drug-soaked gauze for 1 hour immediately after clip removal to attenuate reperfusion injury. Thereafter, drug was applied topically once daily for 4 more days. Digital photographs of each flap were then taken on day 6 and the flaps were then harvested. The percentage of skin survival in each flap was determined by computerized morphometry and planimetry. The mean surviving area of group 3 (oleic acid-treated flaps) was 23.60 +/- 4.19 percent and was statistically higher than that in group 1 (control, saline-treated flaps) at 7.20 +/- 2.56 percent. The mean surviving area of group 2 (dimethyl sulfoxide-treated flaps) at 18.00 +/- 5.23 percent and group 4 (oleic acid- and dimethyl sulfoxide-treated flaps) at 9.90 +/- 3.44 percent did not achieve statistically higher mean surviving areas than controls. A topical solution of oleic acid (10% by volume) caused a statistically significant increase in the survival of rat abdominal skin flaps relative to controls. Dimethyl sulfoxide and the two experimental drugs together did not increase the percentage of flap survival when given as a single 5-ml dose released from a surgical sponge at reperfusion for 1 hour and then daily for a total of 5 days. The reasons for the lack of response are unknown but may have included the technical difficulty of delivering an adequate dose of dimethyl sulfoxide topically and immiscibility between dimethyl sulfoxide and oleic acid. Further studies may be warranted.     

The effect of autologous endothelial progenitor cell transplantation combined with extracorporeal shock-wave therapy on ischemic skin flaps in rats

BackgroundEndothelial progenitor cells (EPCs) have been used to revascularize ischemic tissues, but only limited effect can be achieved. Extracorporeal shock-wave therapy (ESWT) is a promising angiogenic strategy. We hypothesized that EPC transplantation combined with ESWT would greatly benefit the survival of ischemic skin flaps.MethodsSixty-four male Sprague-Dawley rats were divided into 4 groups (n = 16 in each group): group 1 (serving as sham control), group 2 (treated with subcutaneous EPC implantation, 1.0 × 10⁶ cells), group 3 (treated with ESWT, 300 impulses at 0.10 mJ/mm²) and group 4 (treated with EPCs implantation combined with ESWT). Ischemic skin flaps were made on the backs of rats and treated accordingly. Blood flow of skin flaps was measured periodically after operation, and flap survival rates were compared. Tissue samples were harvested at 2 weeks postoperatively from each group.ResultsThe survival rate of skin flaps in group 4 was 87.5 ± 10.23%, which was statistically significantly higher than other groups. Histologic examination showed that the capillary density was higher in the dual-treatment group than in the two single-treatment groups. Compared with groups 2 and 3, blood perfusion increased significantly in group 4. A drastic increase of vWF+ cells was observed in the ischemic skin flaps on immunofluorescence staining in group 4. The expressions of chemotactic factors and angiogenic factors were higher in group 4.ConclusionsCombined treatment with EPCs and ESWT is superior to either EPCs or ESWT alone in improving the survival of ischemic skin flaps in rats.     

Preconditioning of latissimus dorsi muscle flaps with monophosphoryl lipid a

The use of dynamic myoplasty to restore function to failing organs is an exciting new application of skeletal muscle flaps. A complication of large flap elevation that can compromise flap function is ischemia-induced necrosis; one approach to minimizing this is to pretreat tissues with ischemic preconditioning. The purpose of this study was to determine whether systemic administration of monophosphoryl lipid A, a drug known to mimic late-phase ischemic preconditioning in the heart, could reduce ischemia-induced necrosis in latissimus dorsi muscle flaps. Forty latissimus dorsi muscle flaps from 20 Sprague-Dawley rats were allocated into four groups. In group I (n = 10), flaps were not preconditioned and served as controls. In group II (n = 10), flaps received ischemic preconditioning with two 30-minute periods of ischemia interspersed by 10 minutes of reperfusion. In group III (n = 10), rats received an intravenous bolus of approximately 0.3 ml of monophosphoryl lipid A vehicle only. In group IV (n = 10), rats received an intravenous bolus of 450 microg/kg of monophosphoryl lipid A and vehicle. Twenty-four hours after treatment, all latissimus dorsi muscle flaps were elevated on a single neurovascular pedicle and subjected to 4 hours of ischemia. After 72 hours of reperfusion, latissimus dorsi muscles were harvested, weighed, stained with nitroblue tetrazolium, and assessed for percent necrosis using digitized images of muscle sections and computerized planimetry. The percent necrosis in ischemic preconditioning-treated flaps (group II) was significantly reduced by 57 percent (p < 0.05) compared with control flaps (group I). The percent necrosis in flaps treated with monophosphoryl lipid A (group IV) was significantly reduced by 58 percent (p < 0.05) compared with vehicle-control flaps (group III). There was no difference in mean percent necrosis between ischemic preconditioning (group II) and monophosphoryl lipid A-treated (group IV) flaps or between ischemic preconditioning-control (group I) and monophosphoryl lipid A vehicle-control (group III) flaps. Intravenous administration of systemic monophosphoryl lipid A mimics the late-phase protective effect of ischemic preconditioning in the authors' rat latissimus dorsi muscle flap model.     

Comparison of TRAM and DIEP flap physiology in a rat model

Dynamic and physiologic studies objectively comparing the attributes of the transverse rectus abdominis musculocutaneous (TRAM) and deep inferior epigastric perforator (DIEP) flaps would be most practical in an animal model. This has now been accomplished using the ventral abdomen of the Sprague-Dawley rat. A conventional TRAM flap, a multiple perforator DIEP flap, and a solitary perforator DIEP flap were raised in three equal groups of five rats each. Flow studies using laser Doppler flowmetry demonstrated the highest flow in zone I in the TRAM flap group (87.6 +/- 15.4 percent), which was a statistically significant difference from the multiple perforator DIEP flap group (45.4 +/- 13.3 percent) and the solitary perforator DIEP flap group (43.4 +/- 26.4 percent) (p = 0.005). Flow in zone IV was proportionately lower for all groups, with no significant difference noted between TRAM and DIEP flaps (p = 0.736). Although ultimate flap survival was greatest for the TRAM flap group (96.1 +/- 6.7 percent) when compared with the multiple perforator DIEP flap (79.8 +/- 15.2 percent) or the solitary perforator DIEP flap groups (77.1 +/- 23.0 percent), this difference was not statistically significant (p = 0.183). In summary, relative flow to these rat ventral abdomen models was directly proportional to the number of retained musculocutaneous perforators, but a single perforator only could routinely allow near-total survival.     

Improved vitality of experimental random dorsal skin flaps in rats treated with enriched cell culture medium

A defined, serum-free cell culture medium supplemented with nonsteroidal anabolic hormones, insulin, thyroxin, and growth hormone was found to accelerate wound healing by stimulating vascularized granulation tissue formation, epithelialization, and angiogenesis. The aim of this work was to study the effect of cell culture medium on the survival rate of cephalically based random dorsal skin flaps in an animal model. A total of 77 Sprague-Dawley rats were randomized into five treatment groups: pharmacologic delay with cell culture medium, flap enhancement with cell culture medium, surgical delay, biological delay with saline, and control. Statistically significant differences in distal flap necrosis were found among all groups (p<0.003). The rats treated with cell culture medium before flap elevation showed a significant increase in flap viability: a survival rate of 83 percent, compared with the control group, which demonstrated a survival rate of only 58 percent (p<0.0001). The surgical delay and the groups treated with cell culture medium yielded similar results with no significant difference between them. This study indicates that preoperative injection of cell culture medium may play a role in decreasing skin flap necrosis.     

Prevention of ischemia-reperfusion injury in a rat skin flap model: the role of mast cells, cromolyn sodium, and histamine receptor blockade

The objective of this study was to examine the role of mast cells and their principal product, histamine, in ischemia/reperfusion injury. Cromolyn sodium, diphenhydramine, and cimetidine were administered to ischemic flaps just before reperfusion and evaluated for flap survival, mast cell count, neutrophil count, and myeloperoxidase levels. Epigastric island skin flaps were elevated in 49 rats; they were rendered ischemic by clamping the artery for 10 hours. Thirty minutes before reperfusion, the rats were treated with intraperitoneal saline (n = 11), cimetidine (n = 11), diphenhydramine (n = 11), or cromolyn sodium (n = 10). Flap survival was evaluated at 7 days. Neutrophil counts, mast cell counts, and myeloperoxidase levels were evaluated 12 hours after reperfusion. Flap necrosis in the sham group of animals (n = 6) was 0.0 percent, as expected, whereas the control group (saline-treated animals) had 47.3+/-33.4 percent necrosis. Animals treated with diphenhydramine and cimetidine demonstrated a significant decrease in flap necrosis to 17.7+/-8.8 percent and 19.4+/-14.7 percent, respectively. This protective effect was not seen with cromolyn sodium (44.3+/-35.6 percent). Both neutrophil and mast cell counts were significantly decreased in flaps from antihistamine-treated and sham animals versus both saline- and cromolyn sodium-treated groups. The administration of diphenhydramine and cimetidine before reperfusion can significantly reduce the extent of flap necrosis and the neutrophil and mast cell counts caused by ischemia/reperfusion. This protective effect is not seen with cromolyn sodium. The protective effect of antihistamines on flap necrosis might be related to the decrease in neutrophils and, possibly, mast cells within the flap.     

Spinal cord stimulation improves survival in ischemic skin flaps: an experimental study of the possible mediation by calcitonin gene-related peptide

Currently, spinal cord stimulation is used to treat ischemia and ischemic pain, with the best results observed in vasospastic cases. It was earlier demonstrated that spinal cord stimulation may attenuate experimentally induced vasospasm in an island flap in the rat. The present study was designed to investigate whether preemptive spinal cord stimulation could increase long-term flap survival and to explore the neurohumoral mediation of the effect. A total of 56 rats were implanted with chronic spinal cord stimulation systems. Three days later, a groin flap based on the superficial epigastric vessels was harvested, and the single feeding artery was occluded by a detachable microvascular clip. After 12 hours, the clip was removed. Flap survival was evaluated after 7 days. Immediately before flap surgery, two groups of animals received 30 minutes of stimulation using current clinical parameters and with stimulation amplitudes of 70 (n = 10) or 90 percent (n = 8) of that evoking muscular contractions. The outcomes in these groups were compared with those in two control groups (n = 20; n = 10). In one group, an additional calcitonin gene-receptor peptide (CGRP) antagonist was intravenously injected before stimulation (n = 8). In the control groups without stimulation, virtually all flaps necrotized. In treated groups, flap survival was 60 percent at the lower intensity and almost 90 percent at the higher one. The administration of a CGRP antagonist before treatment reduced its efficacy to below 40 percent survival. The differences between the untreated and treated groups were significant. The decrease in survival after CGRP-receptor block was significant in one of two tests. Preemptive spinal cord stimulation increases survival of skin flaps with critical ischemia. The effects are dependent on the stimulation intensity and are possibly mediated by the release of CGRP in the periphery.     

The role of the large superficial vein in survival of proximally based versus distally based sural veno-neuro-fasciocutaneous flaps in a rabbit model

A sural veno-neuro-fasciocutaneous flap in the New Zealand White rabbit was developed, and the role of the large subcutaneous lesser saphenous vein was investigated in proximally based versus distally based flaps. Retrograde dye injection showed that the lesser saphenous vein in rabbits has many valves with strong resistance against reflux. Twenty rabbits were randomly allocated into four groups of 10 flaps each. Group I consisted of proximally based flaps with the lesser saphenous vein intact (outflow) in the veno-neuro-adipofascial pedicle. Group II also consisted of proximally based flaps but the lesser saphenous vein was ligated at 1 cm proximal to the pedicle. Group III consisted of distally based flaps with the lesser saphenous vein intact (inflow) in the veno-neuro-adipofascial pedicle. Group IV also consisted of distally based flaps, but the lesser saphenous vein was ligated at 1 cm distal to the pedicle. The results showed that the mean flap survival area in group I (88.8 percent) was statistically higher than that in group II (62.6 percent, p < 0.001), and was higher in group IV (55.5 percent) than in group III (22.7 percent, p < 0.01). However, group II and group IV had no significant difference (p > 0.05). This experiment demonstrated that flap viability is determined by its intrinsic vascularization, both arterial and venous. The large superficial subcutaneous vein has a positive role (venous outflow) in proximally based flaps but a negative role (venous inflow) in distally based flaps. If the effect of the large subcutaneous vein is excluded, distally based flaps are not inherently inferior to proximally based flaps.     

The effect of carnitine on random-pattern flap survival in rats

Carnitine is an endogenous cofactor involved in the transport of long-chain fatty acids into the mitochondria where they undergo beta-oxidation. Through another reaction, carnitine produces free coenzyme A and reduces the ratio of acetyl-coenzyme A to coenzyme A, thereby enhancing oxidative use of glucose, augmenting adenosine triphosphate synthesis, and reducing lactate production and acidosis. Because of its regulatory action on the energy flow from the different oxidative sources, especially under ischemic conditions, carnitine has been used in cardiovascular diseases such as coronary heart disease, congestive heart failure, peripheral vascular disease, dyslipidemia, diabetes, and chronic renal diseases with satisfactory results. A flap is also a relatively ischemic tissue and may obtain benefit from carnitine. To investigate this, 30 rats were divided into three groups of 10 animals: a control group and two carnitine-treated groups. Random dorsal skin flaps were elevated on the rats. In the control group, no pharmacologic agents were used. Of the two treated groups, group 1 was treated with 50 mg/kg/day carnitine for 1 week and group 2 was treated with 100 mg/kg/day carnitine for 1 week. The areas of flap necrosis were measured in each group. The median areas of flap necrosis of the groups were 12.55, 9.23, and 4.9 cm2, respectively. There was a statistically significant improvement of flap necrosis in carnitine-treated groups compared with the control group (group 2, p = 0.001; group 3, p = 0.000). Furthermore, there was less necrosis in the high-dose carnitine-treated group than the low-dose carnitine-treated group. As a conclusion, carnitine may have a dose-dependent effect to increase flap survival in random skin flaps.     

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.     

Stroma-free hemoglobin: its presence in plasma does not improve oxygen supply to the resting hindlimb vascular bed of hemodiluted dogs.

In hemodilution, red cell spacing in the microcirculation is increased, flow distribution may become more heterogeneous, and, as a result, oxygen supply to tissues may suffer. We tested the hypothesis that oxygen extraction from diluted blood may be enhanced by the presence of hemoglobin in the plasma phase in relatively low concentrations. In anesthetized dogs, the hindlimb vascular bed was isolated and perfused with the animal's own blood by a roller pump. One group of dogs (n = 6) was hemodiluted (hematocrit = 15.0 +/- 1.0%) with a 6% solution of dextran. A second group of dogs (n = 6) was similarly hemodiluted (hematocrit = 16.0 +/- 0.4%) with dextran containing stroma-free hemoglobin solution whereby plasma-phase hemoglobin concentration was raised to 1.1 +/- 0.1 g.dL-1. Systemic hemodynamic observations were made repeatedly over the subsequent 2.5 h, while blood flow to the hindlimb was progressively reduced in stepwise decrements. The hemoglobin-hemodiluted group showed increased systemic arterial blood pressure and total peripheral resistance when compared with the control (dextran diluted) group. The isolated hindlimb also showed evidence of increased vascular resistance in the hemoglobin-treated group. In each individual animal, critical oxygen delivery and extraction were determined by finding the intercept of the supply-independent and supply-dependent portions of the oxygen uptake/oxygen delivery relationship. Neither the critical oxygen delivery rates (5.75 +/- 0.83 vs. 6.41 +/- 0.53 mL.kg-1.min-1) nor critical oxygen extraction ratios (0.75 +/- 0.03 vs. 0.76 +/- 0.04) were found to be significantly different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of low-flow infusion and magnesium on tissue necrosis during regional ischemia in the canine myocardium.

Passive intracoronary perfusion of therapeutic agents has been used in the clinical setting to attenuate the effects of brief episodes of myocardial ischemia. The objective of this study was to assess the effects of low-flow coronary infusion with or without Mg2+ on tissue necrosis and cardiac hemodynamics after prolonged regional ischemia. In 33 anesthetized dogs (5 excluded during study), the left anterior descending coronary artery was occluded for 6 h. Dogs were assigned to three groups: the first group (n = 8) was subjected to 6 h coronary occlusion without low-flow perfusion (controls), the second group (n = 10) received a low-flow coronary infusion of Ringer's lactate (Mg(2+)-free), and the third group (n = 10) received a low-flow coronary infusion of Ringer's lactate plus Mg2+ sulfate (15 mM). Tissue necrosis was evaluated using tetrazolium staining and was normalized to the principal baseline predictors of infarct size including anatomic risk zone (microsphere autoradiography) and coronary collateral flow. In control hearts, infarct size comprised 51.1 +/- 4.1% of the risk zone (40.8 +/- 5.1% left ventricular cross-sectional area (LV)). In the Mg(2+)-free and Mg2+ groups, risk zone size was 17.3 +/- 2.2 and 16.8 +/- 1.8% LV (p < 0.05 vs. controls), while infarct size was 23.1 +/- 3.1 and 24.9 +/- 8.1% (p < 0.05 vs. controls), respectively. Coronary collateral flow in the endocardium was similar for all of the experimental groups; however, hearts subjected to ischemia with low-flow perfusion of Ringer's lactate demonstrated significantly higher epicardial coronary collateral flow levels compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beneficial effects of ibuprofen on experimental microvascular free flaps: pharmacologic alteration of the no-reflow phenomenon

Pharmacologic alteration of the no-reflow phenomenon was determined based on increased tolerance to ischemia in ibuprofen-treated free flaps. Sprague-Dawley rats (N = 60) were divided into control (lactated Ringer's) and treated (ibuprofen) groups and subdivided into six groups of ischemia: 1 hour, 6 hours, 8 hours, 10 hours, 12 hours, and 14 hours of ischemia. Fluorescein uptake was measured after 10, 30, and 60 minutes following microrevascularization. Dye elimination studies were done for each ischemia group that demonstrated good fluorescein uptake. All free flaps in the 1-, 6-, and 8-hour groups survived. The ibuprofen-treated 10- and 12-hour flaps all survived, whereas the 10-hour control and 14-hour ibuprofen-treated free flaps failed to survive. Despite high fluorescein uptake, the 14-hour ibuprofen-treated flaps did not eliminate the fluorescein, whereas all surviving free flaps adequately eliminated the fluorescein. Failure to eliminate dye despite adequate uptake suggested a deranged microcirculation with increasing ischemia time. By inhibiting cyclo-oxygenase, nonsteroidal anti-inflammatory agents such as ibuprofen may block the untoward effects mediated by thromboxane A2, such as vasoconstriction, microvasculature thrombus formation, and intravascular sludging. These effects are theorized in part to be responsible for the failure of a free flap to survive despite revascularization.     

The influence of pentoxifylline on skin-flap survival

Experimental studies were performed on rats to demonstrate the effects of pentoxifylline (20 mg/kg per day), administered enterally, on skin-flap viability. This was compared to saline controls and to the alpha-blocking agent (phenoxybenzamine 1 mg/kg per day). Pentoxifylline-treated flaps had a greater than 50 percent increase in tissue survival over controls as compared to 22 percent with phenoxybenzamine. The two drugs in combination appeared to have no additional benefit over the use of pentoxifylline alone. Although a quantitative difference in red-cell flow could not be demonstrated in the experimental flaps utilizing 99mTc pertechnetate-tagged red-cell imaging, the dramatic increase in tissue viability suggests that the rheologic properties of pentoxifylline are important in altering the pathophysiology of skin-flap failure.     

Effects of phentolamine on hepatic PO2 in endotoxemia

The effect of phentolamine, an alpha-adrenergic blocker, on hepatic oxygen supply, plasma glucose, and lactate, and survival in fasted male rats administered Echerichia coli endotoxin (25 mg/kg, ip) has been studied. Survival at 24 h was 8% in untreated endotoxic rats, 83% in rats receiving phentolamine (5 mg/kg, ip) and endotoxin, and 100% in phentolamine controls. Measurements during the initial 8 h postendotoxin recorded transiently lower systemic arterial pressure in the phentolamine-endotoxic rats. Arterial PO2 and increases of pH and heart rate were similar in both endotoxic groups. Lactacidemia, present by 4 h in untreated endotoxic rats, did not develop in the phentolamine group and plasma glucose was significantly higher at 8 h (98 +/- 2.5 vs. 77 +/- 5.6 mg%, mean +/- SE). Mean hepatic PO2 at 6 h in phentolamine-endotoxic rats was 9.6 mmHg with 28% of the values below 5 mmHg. By contrast, the mean in untreated endotoxic rats was 1.9 mmHg with 88% of values below 5 mmHg. Phentolamine controls were stable over 8 h; mean hepatic PO2 was 17.7 mmHg. The differences in plasma glucose and lactate suggest protection of hepatic metabolism in phentolamine-treated endotoxic rats by prevention of excessive hepatic hypoxia.