The Effect of Ischemic Preconditioning on Secondary Ischemia in Skin Flaps

The current state of knowledge on how to improve skin flap survival: A review

The incorporation of skin flaps in wound closure management with its cosmetic implications has appeared as a gleam of hope in providing desirable outcomes. Given the influence of extrinsic and intrinsic factors, skin flaps are prone to several complications, including ischemia-reperfusion injury (IRI). Numerous attempts have been undertaken to enhance the survival rate of skin flaps entailing pre/post-conditioning with surgical and pharmacological modalities. Various cellular and molecular mechanisms are employed in these approaches in order to reduce inflammation, promote angiogenesis and blood perfusion, and induce apoptosis and autophagy. With the emerging role of multiple stem cell lineages and their ability to improve skin flap viability, these approaches are increasingly being used to develop even more translationally applicable methods. Therefore, this review aims at providing current evidence around pharmacological interventions for improving skin flap survival and discussing their underlying mechanism of action.

Protective Effect of Ebselen on Ischemia-reperfusion Injury in Epigastric Skin Flaps in Rats

The purpose of this study was to determine the role of oxidized diacylglycerol (DAG) and the molecular mechanism underlying ischemia-reperfusion (I/R) injury in rat skin flaps. The protective effect of ebselen on the viability of rat skin flaps with I/R injury was investigated. Flaps were designed and raised in the left inguinal region. Then, a microvascular clamp was applied to the vascular pedicle and reperfused after 6 hr. After 7 days of I/R (I/R group), the skin flap survival area ratio was significantly reduced compared to the normal skin. The administration of ebselen significantly improved the ratio compared to the I/R group. The flap survival area ratio of the I/R + ebselen group was significantly improved compared to the I/R + vehicle group. In the I/R + ebselen group, the oxidized DAG content and intensity of phosphorylated PKCα and PKCδ were significantly lower compared to the I/R + vehicle group. Furthermore, the inflammatory response was suppressed in the I/R + ebselen group compared to the I/R + vehicle group. These results indicate that ebselen is useful as a preventive and therapeutic agent for skin flap necrosis caused by I/R, because of reduction and elimination of oxidized DAG.

Effects of Ischemic Preconditioning and C1 Esterase Inhibitor Administration following Ischemia-Reperfusion Injury in a Rat Skin Flap Model

BACKGROUND

 Ischemia-reperfusion (I/R) injury is a serious condition that can affect the success rate of microsurgical reconstructions of ischemic amputated limbs and complex tissue defects requiring free tissue transfers. The purpose of this study was to evaluate the effects of ischemic preconditioning (IPC) and C1 esterase inhibitor (C1-Inh) intravenous administration following I/R injury in a rat skin flap model.

METHODS

 Superficial caudal epigastric skin flaps (3 cm × 7 cm) were performed on 50 Wistar rats that were randomly divided into five groups. Ischemia was not induced in the control group. All other flaps underwent 8 hours of ischemia prior to revascularization: I/R control group (8-hour ischemia), IPC group (preconditioning protocol + 8-hour ischemia), C1-Inh group (8-hour ischemia + C1-Inh), and IPC + C1-Inh group (preconditioning protocol + 8-hour ischemia + C1-Inh). Survival areas were macroscopically assessed after 1 week of surgery, and histopathological and biochemical evaluations were also measured.

RESULTS

 There were no significant differences in flap survival between the treatment groups that were suffering 8 hours of ischemia and the control group. A significant increase in neovascularization and lower edema formation were observed in the IPC group compared with that in the I/R group. Biochemical parameters did not show any significant differences.

CONCLUSION

 Intravenous administration of C1-Inh did not significantly modulate I/R-related damage in this experimental model, but further research is needed. On the other hand, IPC reduces tissue damage and improves neovascularization, confirming its potential protective effects in skin flaps following I/R injury.

Combination of ischemic preconditioning and postconditioning can minimise skin flap loss: experimental study

OBJECTIVES

Ischaemic preconditioning and postconditioning, which consist of one or a series of short ischaemic events. This study aimed to determine the efficiency of post-conditioning a flap in the minimisation of flap loss after a preconditioned skin flap.

METHODS

The rats were divided into five groups: sham group, control group, pre-con group, post-con group, and pre + post-con group. On postoperative days 3 and 7, the entire flaps along with the margins of necrosis were traced onto transparent sheets. The areas of intact skin and tissue were recorded.

RESULTS

The flap necrosis area and percentage of necrosis were calculated for each animal. The necrotic area percentage of the control group was found to be significantly higher than those of the other groups on Days 3 and 7 (p = 0.01 and p = 0.03, respectively). The necrotic area percentage of the pre-con group was significantly higher than the pre + post-con group on Day 7 (p = 0.01). VEGFR-3 expression was observed at a rate of more than 50% in the post-con group. The presence of a protective effect in the late period was separately investigated by immunohistochemical staining of VEGFR-3 in the proliferating vessels. The necrotic areas was reduced in the flaps of the pre-con, post-con, and pre + post-con groups and the combined preconditioning and postconditioning group has reduced necrotic area compared to preconditioning of the skin flap.

CONCLUSION

The protective effect was observed on day 7 for combined ischaemic preconditioning and postconditioning. The presence of a protective effect in the late period was separately investigated by immunohistochemical staining of VEGFR-3 in the proliferating vessels.

Comparing different postconditioning cycles after ischemia reperfusion injury in the rat skin flap

Ischemic postconditioning is a useful manipulation to reduce the undesirable effects of ischemia-reperfusion (I/R) injury. The beneficial results of this phenomenon against I/R injury have been seen in several flap models. However, there are no published works comparing different postconditioning (post-con) cycles in skin flaps. In this study, we investigated the effectiveness of different post-con cycles in a skin flap model. Epigastric island flap (6 × 3 cm) model which was based on the left superficial epigastric artery and vein was used, and complete 6 hours of ischemia was generated by occlusion of the pedicle. Forty male Wistar rats were allocated into 5 groups (n = 8 in each group). Group 1 (sham group): the elevated skin flap was repositioned without an episode of ischemia. Group 2 (control group): skin flap was elevated and 6 hours of complete ischemia was induced by clamping the pedicle. Group 3 (post-con 1): After ischemia, post-con was performed by 6 cycles of 15 seconds of repeated I/R periods. Group 4 (post-con 2): After ischemia, post-con was performed by 6 cycles of 30 second of repeated I/R periods. Group 5 (post-con 3): After ischemia, post-con was performed by 6 cycles of 60 second of repeated I/R periods. Flap viability was assessed 1 week after the surgical procedure, the necrotic area of the skin flap was measured using image analysis on the computer. The area of flap necrosis was statistically significant between the control and post-con group 4 and group 5, and no statistically significant difference was obtained between the control and post-con group 3. Groups 4 and 5 demonstrated lesser area of flap necrosis than the control group and group 4 was superior to group 5. The results revealed that the post-con applied by means of 6 cycles of 30 seconds yields the best protection against I/R injury in the rat skin flap model.

The effectiveness of pedicled groin flaps in the treatment of hand defects: results of 49 patients

PURPOSE

Despite the growing number of free and local flaps used for repairing defects of the hand, groin flaps are also still widely used. The aims of this study were to evaluate the outcome of a large series of patients whose defects were covered by pedicled groin flaps, and to find out whether it is still indicated in replacing damaged soft tissue of the hand in the era of microsurgery.

METHODS

From 1982 to 2009, we treated 85 patients with soft tissue defects on the hand and distal forearm with pedicled groin flaps in our department and recorded them in a prospective database. We interviewed and examined 49 patients in this cohort.

RESULTS

The mean age of the 85 patients was 33 years, the male/female ratio was 4:1, the mean hospital stay was 29 ± 13 days, and the mean follow-up was 9 years. The duration to flap division was 24 ± 5 days. Altogether, we performed a mean of 4.6 operations per patient, including thinning of the flap, deepening of the interdigital fold, and stump and flap revisions. One flap loss occurred. Of the 49 patients, results were mostly classified as good, and 82% of patients would undergo the procedure again. The mean Disabilities of the Arm, Shoulder, and Hand score value was 23 ± 17. The Vancouver Scar Scale showed nearly normal height and vascularity of the groin flap (0.2 ± 0.4 and 0.3 ± 0.6, respectively), pigmentation was slightly abnormal (0.8 ± 0.6), and pliability was evaluated between "supple" and "yielding" (1.5 ± 1.2).

CONCLUSIONS

Results achieved with the groin flaps were positive. Most patients were satisfied with the results, and the operation was easily performed when McGregor's recommendations were followed. Nevertheless, considering the high number of secondary operations, the long hospital stay, and immobilization of the arm, groin flaps should be used only when free flaps or regional pedicle flaps are either not feasible or not indicated.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic III.

The impact of lidocaine on secondary ischemia injury of skin flaps

PURPOSE

Lidocaine is used to reduce the undesirable effects of ischemia because of its anti-inflammatory effects. Herein we investigated the effects of lidocaine on secondary ischemia in a skin flap model.

MATERIALS AND METHODS

In this epigastric skin flap protocol in animals, we followed 2 hours of primary global ischemia with a reperfusion period of 6 hours and then either secondary arterial or venous ischemia for another 6 hours during which we tested the usefulness of lidocaine. Lidocaine was injected via the intraperitoneal route 5 minutes before the second period of ischemia. The animals were allocated into secondary arterial ischemia or secondary venous ischemia groups which were subdivided according to the delivered agents. Neutrophil cell counts at the margins of the flaps were recorded 12 hours after the end of the second period of ischemia. Flap viability was assessed 1 week after the surgical procedure. Surviving flap area was recorded as the percentage of the whole area. The Least Significant Difference test was used to detect a significant difference among groups, and the Pearson test to evaluate the relationship between neutrophil counts and flap survival rate.

RESULTS

There were significant differences among groups both with respect to neutrophil count and flap survival. There was a relationship between the neutrophil counts and the flap survivals.

CONCLUSION

Intraperitoneally injected lidocaine was an effective procedure to reduce flap necrosis as a cause of secondary ischemia in skin flaps, an effect of the ischemia-reperfusion injury.

Intermittent ischaemia of skin flaps shortens time taken to divide pedicles: an experimental study in rats

Ischaemic preconditioning increases the survival of flaps. Random-pattern McFarlane dorsal flaps were raised in 30 female Wistar rats, which were divided into three groups. An ischaemic conditioning protocol with clamping of the pedicle was used. No clamping was used in the control group, and the pedicle was clamped for 15 minutes in the second group and 20 minutes in the third group daily to see if the duration of ischaemia had any effects on the viability of the flaps. The pedicles were divided earlier in the clamped groups than in the control group. The size of necrotic areas of the flaps in the clamped groups was smaller than on the control group. Daily postoperative intermittent ischaemic conditioning in the pedicles of the flaps had a protective effect on their survival and led to earlier division of the pedicles.

Effect of cyclooxygenase-2 on ischemic preconditioning of skin flaps

Ischemic preconditioning is a useful tool to fight against reperfusion injury. This phenomenon is very complex and the underlying mechanism has various branches. Every study on ischemic preconditioning helps us to better understand this process. We aimed to investigate the effectiveness of cyclooxygenase-2 (COX-2) on ischemic preconditioning of skin flaps in the rat. A 6 x 3 cm-sized left epigastric artery flap was used and the pedicle was isolated to perform the ischemic preconditioning via microvascular clamp application. The preconditioning protocol was 2 cycles of 15 minutes ischemia and 15 minutes reperfusion periods. Sixty female Wistar rats weighing between 210 and 260 g were used for the experiment. Animals were allocated randomly into 6 groups, each group containing 10 animals. Group 1: Only 6 hours of ischemia was done after the flap elevation, neither ischemic preconditioning nor COX-2 inhibitor was used; Group 2: 6 hours of global ischemia was induced just after the ischemic preconditioning; Group 3: In addition to the same procedures in group 2, 2 doses of COX-2 inhibitor were given before and after the final ischemic insult; Group 4: 6 hours of ischemia was applied to the flap 24 hours after its elevation, no preconditioning or any other interventions were done; Group 5: The same ischemic protocol was used after the flap elevation but the 6 hours of ischemia was performed 24 hours after the preconditioning; Group 6: The same procedures of group 5 were done and in addition, 2 doses of COX-2 inhibitor was given, starting 24 hours after the ischemic preconditioning. All flaps were followed for 1 week then necrotic flap portions were measured and represented as a percentage to the whole flap area. Statistical analyses revealed meaningful differences between groups 2 and 3 (P < 0.05), 2 and 1 (P < 0.05), 5 and 6 (P < 0.05), 5 and 4 (P < 0.05). However, there was no statistical difference between groups 3 and 1 (P > 0.05), 6 and 4 (P > 0.05). As a conclusion, ischemic preconditioning has both early and late protective effects on ischemia-reperfusion injury in the skin flap model. By antagonizing COX-2 receptors the beneficial effects of IP were reversed. This result indicated that COX-2 has a specific role in the mechanism of both early and late effects of ischemic preconditioning in skin flaps.

Investigation of reperfusion injury and ischemic preconditioning in microsurgery

Ischemia/reperfusion (I/R) is inevitable in many vascular and musculoskeletal traumas, diseases, free tissue transfers, and during time-consuming reconstructive surgeries in the extremities. Salvage of a prolonged ischemic extremity or flap still remains a challenge for the microvascular surgeon. One of the common complications after microsurgery is I/R-induced tissue death or I/R injury. Twenty years after the discovery, ischemic preconditioning has emerged as a powerful method for attenuating I/R injury in a variety of organs or tissues. However, its therapeutic expectations still need to be fulfilled. In this article, the author reviews some important experimental evidences of I/R injury and preconditioning-induced protection in the fields relevant to microsurgery.

A novel murine island skin flap for ischemic preconditioning

BACKGROUND

Ischemia reperfusion injury is a well-known phenomenon affecting skin flap viability. One method to improve flap viability is ischemic preconditioning. Previous murine flap models used random flaps. We developed a single pedicle island skin flap which allows us to create true ischemia by clamping the single pedicle. Our first aim was to describe a novel murine skin flap model with a definable, reproducible injury. Our second aim was to test the usefulness of this model by demonstrating mitigation of injury via ischemic preconditioning.

MATERIALS AND METHODS

Dorsal lateral thoracic artery pedicle island skin flaps (3.5 x 1.5 cm) were elevated in 39 male C57/BL6 mice: a Control group (n = 7), 10 h of ischemia (n = 21), and Preconditioning (2 cycles of 20 min ischemia: 20 minutes reperfusion) + 10-h ischemia (n = 11). After flap elevation, a silicon sheet barrier was placed. The axial pedicles were occluded, and the flaps were inset with 6-0 prolene. In all mice, ischemia was followed by 1 wk of reperfusion. At 1 wk, percent necrosis was measured and an analysis of variance was performed.

RESULTS

The percent of flap necrosis was 1.1% +/- 1.11% in controls. Animals that were subjected to 10 h of ischemia developed 33.14% +/- 7.23% necrosis. Preconditioned animals that underwent 10 h of ischemia demonstrated a 43% reduction in necrosis (18.82% +/- 5.68%). There was a statistically significant difference among all groups (P < or = 0.001).

CONCLUSION

Rat models have been the standard for skin flap experiments. We have developed a novel murine single pedicle island skin flap model with reproducible injury. This model has numerous advantages, including ease of handling, low cost, appropriateness for biomedical studies, and the availability of genetically altered animals. We also confirmed this model's usefulness in a study of mitigation of ischemia reperfusion injury through ischemic preconditioning.

Ischemic preconditioning of skeletal muscle mitigates remote injury and mortality

BACKGROUND

Ischemic preconditioning (IPC) mitigates ischemia-reperfusion (I/R) injury in experimental models. However, the clinical significance of this protection has been unclear and a mortality reduction has not been previously reported in noncardiac models. This study examined the local and remote protection afforded by skeletal muscle IPC and sought to determine the significance of this protection on mortality.

METHODS

Mice subjected to 2 h hindlimb ischemia/24 h reperfusion (standard I/R injury) were compared with those undergoing a regimen of two 20-min cycles of IPC followed by standard I/R injury. Local injury was assessed via gastrocnemius histology, and remote injury was evaluated via intestinal histology and pulmonary neutrophil infiltration (n = 7). Mortality was compared in parallel groups for 1 week (n = 6). Groups were analyzed using an unpaired Student's t-test for gastrocnemius and pulmonary injury, and a Mann-Whitney rank sum test for intestinal injury. Mortality differences were interpreted through a hazard ratio.

RESULTS

Significant protection was observed in preconditioned animals. There was a 35% local injury reduction in skeletal muscle (71.2% versus 46.0%, P < 0.01), a 50% reduction in remote intestinal injury (2.3 versus 1.1, P < 0.01), and a 43% reduction in remote pulmonary injury (14.9 versus 8.5, P < 0.01) compared with standard injury controls. Preconditioned animals were also significantly protected from mortality, demonstrating a 66.7% survival at 1 wk compared with 0% survival after standard injury alone (hazard ratio 0.20, 95% CI: 0.02-0.59).

CONCLUSIONS

We have developed a murine model of IPC that demonstrates local and remote protection against I/R injury, and exhibits significant mortality reduction. This model demonstrates the powerful effect of IPC on local and remote tissues and will facilitate further study of potential mechanisms and therapies.