An old dream revitalised: preconditioning strategies to protect surgical flaps from critical ischaemia and ischaemia-reperfusion injury

Phosphatidylserine accelerates wound healing and reduces necrosis in the rats: Growth factor activation

To examine the effect of topical phosphatidylserine (PS) on wound healing factors and tissue necrosis in in vivo models. Topical PS was applied to evaluate aspects of the wound healing process and growth factors production of vascular endothelial growth factors (VEGF) as well a necrosis reduction in the skin flap of rat models. Moreover, phenytoin (PHT) and cyclosporine A (CsA) were used topically as positive control treatments in wound and necrosis models, respectively. Immunohistochemistry (IHC) VEGF, transforming growth factor-β (TGF-β), fibroblast growth factor (FGF) and histopathology were analysed on the wounds of rats. In the necrosis assessment, necrotic areas were determined on photography taken from the back skin of rats. Results indicated that PS topically enhanced significantly (P < 0.05) numbers of fibroblasts and endothelium while inhibiting the neutrophils and macrophages during the 14 days of wound treatment. Moreover, higher values of collagen deposition and epithelialization scores as well as wound recovery percentage (near 80%) were determined significantly (P < 0.05) in the PS group compared with the control. IHC analysis determined that FGF and VEGF cytokine factors were elevated in the wound site by topical PS. Moreover, the necrotic area was significantly (P < 0.05) improved in the PS group. Our experiment indicated that wound improvement and flap survival values in PS treatments were superior to PHT and CsA control groups, respectively. In conclusion, these findings suggest the potential of PS application in the healing of wounds and control of necrosis development after surgery or skin injuries.

VEGF and Other Gene Therapies Improve Flap Survival-A Systematic Review and Meta-Analysis of Preclinical Studies

Surgical flaps are basic tools in reconstructive surgery. Their use may be limited by ischemia and necrosis. Few therapies address or prevent them. Genetic therapy could improve flap outcomes, but primary studies in this field present conflicting results. This systematic review and meta-analysis aimed to appraise the efficacy of external gene delivery to the flap for its survival in preclinical models. This review was registered with PROSPERO (CRD42022359982). PubMed, Embase, Web of Science, and Scopus were searched to identify studies using animal models reporting flap survival outcomes following any genetic modifications. Random-effects meta-analysis was used to calculate mean differences in flap survival with accompanying 95% CI. The risk of bias was assessed using the SYRCLE tool. Subgroup and sensitivity analyses were performed to ascertain the robustness of primary analyses, and the evidence was assessed using the GRADE approach. The initial search yielded 690 articles; 51 were eventually included, 36 of which with 1576 rats were meta-analyzed. VEGF gene delivery to different flap types significantly improved flap survival area by 15.66% (95% CI 11.80-19.52). Other interventions had smaller or less precise effects: PDGF-13.44% (95% CI 3.53-23.35); VEGF + FGF-8.64% (95% CI 6.94-10.34); HGF-5.61% (95% CI 0.43-10.78); FGF 3.84% (95% CI 1.13-6.55). Despite considerable heterogeneity, moderate risk of bias, and low quality of evidence, the efficacy of VEGF gene therapy remained significant in all sensitivity analyses. Preclinical data indicate that gene therapy is effective for increasing flap survival, but further animal studies are required for successful clinical translation.

In Situ Monitoring and Assessment of Ischemic Skin Flap by High-Frequency Ultrasound and Quantitative Parameters

Skin flap surgery is a critical procedure for treating severe skin injury in which post-surgery lesions must well monitored and cared for noninvasively. In the present study, attempts using high-frequency ultrasound imaging, quantitative parameters, and statistical analysis were made to extensively assess variations in the skin flap. Experiments were arranged by incising the dorsal skin of rats to create a skin flap using the chamber model. Measurements, including photographs, 30 MHz ultrasound B-mode images, skin thickness, echogenicity, Nakagami statistics, and histological analysis of post-surgery skin flap, were performed. Photograph results showed that color variations in different parts of the skin flap may readily correspond to ischemic states of local tissues. Compared to post-surgery skin flap on day 7, both integrated backscatter (IB) and Nakagami parameter (m) of the distal part of tissues were increased, and those of the skin thickness were decreased. Overall, relative skin thickness, IB, and m of the distal part of post-surgery skin flap varied from 100 to 67%, -66 to -61 dB, and 0.48 to 0.36, respectively. These results demonstrate that this modality and quantitative parameters can be feasibly applied for long-term and in situ assessment of skin flap tissues.

Hypoxic mesenchymal stem cell-derived exosomes promote the survival of skin flaps after ischaemia-reperfusion injury via mTOR/ULK1/FUNDC1 pathways

Flap necrosis, the most prevalent postoperative complication of reconstructive surgery, is significantly associated with ischaemia-reperfusion injury. Recent research indicates that exosomes derived from bone marrow mesenchymal stem cells (BMSCs) hold potential therapeutic applications in several diseases. Traditionally, BMSCs are cultured under normoxic conditions, a setting that diverges from their physiological hypoxic environment in vivo. Consequently, we propose a method involving the hypoxic preconditioning of BMSCs, aimed at exploring the function and the specific mechanisms of their exosomes in ischaemia-reperfusion skin flaps. This study constructed a 3 × 6 cm2 caudal superficial epigastric skin flap model and subjected it to ischaemic conditions for 6 h. Our findings reveal that exosomes from hypoxia-pretreated BMSCs significantly promoted flap survival, decrease MCP-1, IL-1β, and IL-6 levels in ischaemia-reperfusion injured flap, and reduce oxidative stress injury and apoptosis. Moreover, results indicated that Hypo-Exo provides protection to vascular endothelial cells from ischaemia-reperfusion injury both in vivo and in vitro. Through high-throughput sequencing and bioinformatics analysis, we further compared the differential miRNA expression profiles between Hypo-Exo and normoxic exosomes. Results display the enrichment of several pathways, including autophagy and mTOR. We have also elucidated a mechanism wherein Hypo-Exo promotes the survival of ischaemia-reperfusion injured flaps. This mechanism involves carrying large amounts of miR-421-3p, which target and regulate mTOR, thereby upregulating the expression of phosphorylated ULK1 and FUNDC1, and subsequently further activating autophagy. In summary, hypoxic preconditioning constitutes an effective and promising method for optimizing the therapeutic effects of BMSC-derived exosomes in the treatment of flap ischaemia-reperfusion injury.

Effects of pharmacological delay with roxadustat on multi-territory perforator flap survival in rats

Roxadustat (FG-4592) is a specific hypoxia-inducible factor (HIF) prolyl hydroxylase inhibitor. We investigated the effects of FG-4592 pretreatment on survival and second choke vessels of multi-territory perforator flaps in rats. In total, 72 rats were divided into two groups (n = 36 each): the experimental (FG-4592) group and the control group. FG-4592 was administered orally as a single dose of 60 mg/kg every other day; the first drug solution was administered to the animals 7 days before the surgical procedure. On postoperative day 7, the surviving flap area was calculated. At 12 h post-surgery, in the second choke zone in the flaps, macrovascular hinges were compared by angiography and imaging, and microvascular changes were assessed by histology. Laser Doppler imaging was used to evaluate flap perfusion at the second choke zone at 12 h and 7 days after surgery. At 7 days after surgery, the flap survival area and perfusion were significantly greater in rats given FG-4592 compared with controls. At 12 h after surgery, the diameter of macrovascular and microvascular vessels, nitric oxide content, perfusion, and the protein levels of HIF-1α and inducible nitric oxide synthase were also significantly greater in FG-4592-treated rats than controls. In conclusion, pretreatment with roxadustat may improve initial flap survival and dilate the second choke zone vessels in a multi-territory perforator flap.

Oxidative stress-induced endothelial cells-derived exosomes accelerate skin flap survival through Lnc NEAT1-mediated promotion of endothelial progenitor cell function

Background

Flap transplantation is commonly used in reconstructive surgery. A prerequisite for skin flap survival is sufficient blood supply. However, such approaches remain unclear. This study aimed to explore the underlying mechanisms of exosomes derived from human umbilical vascular endothelial cells (HUVECs) exposed to oxidative stress on endothelial progenitor cells (EPCs) and their subsequent influence on the survival of skin flaps.

Methods

HUVECs were treated with various concentrations of H₂O₂ to establish an oxidative stress model. To investigate the effects of H₂O₂-HUVEC-Exos and HUVEC-Exos, Cell Counting Kit-8, tube formation, invasion assays, and quantitative real-time polymerase chain reaction (qRT-PCR) were performed in EPCs. Microarray analysis was used to reveal the differentially expressed long non-coding RNAs (lncRNAs) in the H₂O₂-HUVEC-Exos and HUVEC-Exos. In addition, gene silencing and western blotting were employed to determine the mechanism behind lncRNA nuclear enrichment enriched transcript 1 (Lnc NEAT1) in EPCs. Further, a rat skin flap model was used to determine the role of the exosomes in skin flap survival in vivo.

Results

HUVECs were stimulated with 100 μmol/L H₂O₂ for 12 h to establish an oxidative stress model. H₂O₂-HUVEC-Exos promoted the proliferation, tube formation, and invasion of EPCs and remarkably increased skin flap survival compared to the HUVEC-Exos and control groups. Sequencing of exosome RNAs revealed that the Lnc NEAT1 level was dramatically increased in the H₂O₂-HUVEC-Exos, leading to activation of the Wnt/β-catenin signaling pathway. Comparatively, knockdown of Lnc NEAT1 in HUVEC-Exos and H₂O₂-HUVEC-Exos significantly inhibits the angiogenic capacity of EPCs, reduced the survival area of skin flap and downregulated the expression levels of Wnt/β-catenin signaling pathway proteins, whereas Wnt agonist partly reversed the negative effect of NEAT1 downregulation on EPCs through the Wnt/β-catenin signaling pathway.

Conclusions

Exosomes derived from HUVECs stimulated by oxidative stress significantly promoted the pro-angiogenic ability of EPCs through the Wnt/β-catenin signaling pathway mediated by Lnc NEAT1 and hence enhanced random flap survival in vivo. Therefore, the application of H₂O₂-HUVEC-Exos may serve as an alternative therapy for improving random skin flap survival.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03013-9.

Improving Vascularization of Biomaterials for Skin and Bone Regeneration by Surface Modification: A Narrative Review on Experimental Research

Artificial tissue substitutes are of great interest for the reconstruction of destroyed and non-functional skin or bone tissue due to its scarcity. Biomaterials used as scaffolds for tissue regeneration are non-vascularized synthetic tissues and often based on polymers, which need ingrowth of new blood vessels to ensure nutrition and metabolism. This review summarizes previous approaches and highlights advances in vascularization strategies after implantation of surface-modified biomaterials for skin and bone tissue regeneration. The efficient integration of biomaterial, bioactive coating with endogenous degradable matrix proteins, physiochemical modifications, or surface geometry changes represents promising approaches. The results show that the induction of angiogenesis in the implant site as well as the vascularization of biomaterials can be influenced by specific surface modifications. The neovascularization of a biomaterial can be supported by the application of pro-angiogenic substances as well as by biomimetic surface coatings and physical or chemical surface activations. Furthermore, it was confirmed that the geometric properties of the three-dimensional biomaterial matrix play a central role, as they guide or even enable the ingrowth of blood vessels into a biomaterial.

Effects of Preconditioning With Transcutaneous Electrical Nerve Stimulation Monitored by Infrared Thermography on the Survival of Pedicled Perforator Flaps in a Rat Model

OBJECTIVE

Pedicled perforator partial or complete necrosis with a rate of 13.7%. This study was undertaken to test whether preconditioning with transcutaneous electrical nerve stimulation (TENS) monitored by infrared thermography protect against partial necrosis by converting the choke anastomoses to the true anastomoses via inducing heme oxygenase-1 (HO-1) in a rat pedicled perforator flap model.

METHODS

Seventy-two Sprague-Dawley rats were randomly assigned to the control, the TENS, the TENS + SnPP (tin protoporphyrin; HO-1 activity inhibitor; 50 μmol/kg) and the TENS +0.9% saline groups. On the unilateral dorsum of the rats, a rectangular flap donor site of 11 × 3 cm was marked out, which contained three perforator angiosomes and two choke zones. On days 1, 3 and 4, 1 hour of TENS (biphasic pulses, 25 mA, 80 Hz, 200 μs) was applied to the flap donor sites, respectively. On day 5, after the flap donor sites were assessed by infrared thermography, the flaps were harvested based on the deep circumflex iliac artery perforator.

RESULTS

Infrared thermography showed that the choke zones in the flap donor sites presented white in the TENS and the TENS +0.9% saline groups, whereas they presented red in the control and the TENS + SnPP groups. Postmortem arteriography showed that the number of arterioles across each choke zone significantly increased in the TENS and the TENS +0.9% saline groups compared with the control and the TENS + SnPP groups. Immunohistochemistry and western blot showed a significant increase in HO-1 in the choke zones after TENS preconditioning. The necrotic area percentage of the flaps was significantly decreased in the TENS (4.3% ± 2.6%) and the TENS +0.9% saline groups (4.5% ± 2.3%) compared with the control (24.8% ± 5.0%) (P < 0.001); there was no significant difference between the TENS and the TENS + SnPP (24.4% ± 7.3%) groups.

CONCLUSIONS

These data show that TENS preconditioning monitored by infrared thermography might be a promising strategy to prevent pedicled perforator flaps from partial necrosis.

Effects of ischemic conditioning on head and neck free flap oxygenation: a randomized controlled trial

Flap failure after microvascular reconstructive surgery is a rare but devastating complication caused by reperfusion injury and tissue hypoperfusion. Remote ischemic conditioning (RIC) provides protection against ischemia/reperfusion injury and reduces tissue infarction. We hypothesized that RIC would enhance flap oxygenation and exert organ-protective effects during head and neck free flap reconstructive surgery. Adult patients undergoing free flap transfer surgery for head and neck cancer were randomized to receive either RIC or sham-RIC during surgery. RIC consisted of four cycles of 5-min ischemia and 5-min reperfusion applied to the upper or lower extremity. The primary endpoint, tissue oxygen saturation of the flap, was measured by near-infrared spectroscopy on the first postoperative day. Organ-protective effects of RIC were evaluated with infarct size of rat hearts perfused with plasma dialysate from patients received RIC or sham-RIC. Between April 2018 and July 2019, 50 patients were randomized (each n = 25) and 46 were analyzed in the RIC (n = 23) or sham-RIC (n = 23) groups. Tissue oxygen saturation of the flap was similar between the groups (85 ± 12% vs 83 ± 9% in the RIC vs sham-RIC groups; P = 0.471). Myocardial infarct size after treatment of plasma dialysate was significantly reduced in the RIC group (44 ± 7% to 26 ± 6%; P = 0.018) compared to the sham-RIC group (42 ± 6% to 37 ± 7%; P = 0.388). RIC did not improve tissue oxygenation of the transferred free flap in head and neck cancer reconstructive surgery. However, there was evidence of organ-protective effects of RIC in experimental models.

Trial registration: Registry number of ClinicalTrials.gov: NCT03474952.

The Effect of Ceruloplasmin Against Ischemia-Reperfusion Injury in Epigastric Island Flap in Rats

BACKGROUND

Flap surgery is frequently used in plastic surgery to close tissue defects. Ischemia-reperfusion (I/R) injury is a significant problem resulting in partial or total flap necrosis. This study aimed to investigate the effect of ceruloplasmin on I/R injury in epigastric island flaps in rats.

MATERIAL AND METHOD

A total of 32 male Sprague-Dawley rats were divided into four groups with eight rats in each group: The flap was not elevated in Group I; the flap was elevated without ischemia or any application in Group II, after the intraperitoneal saline and ceruloplasmin application the flaps were elevated and ischemia was created in group III-IV, respectively. Bilateral epigastric artery flap was elevated in all groups except Group I. After 6 h of ischemia, the flap was reperfused and inset. Samples were taken from the right and left side of the flap area in other groups at the postoperative 24th h for biochemical analysis (catalase and malondialdehyde-MDA) and the seventh postoperative day for histopathological analysis (Modified Verhofstad score and epidermal thicknesses), respectively. Image analysis for necrosis areas was performed on photos taken on the 7th d.

RESULTS

Catalase level was significantly higher in Group IV.(0.15 ± 0.04 U/mg protein) (P < 0.05) Necrosis area percentage(14.4% ± 3.3%),MDA(3.6 ± 0.9 nmol/mg protein), edema(3), necrosis(2.75), and polymorphonuclear leukocyte infiltration(2.87) scores were significantly higher in group III.(P < 0.05). Fibroblast proliferation, collagen density (0.25), vascular density (0.25) scores and epidermal thickness (15.68 µm,) was significantly lower in group III. (P < 0.05) CONCLUSIONS: Our study demonstrated that ceruloplasmin application before ischemia reduced I/R injury in epigastric island flaps in rats.

Improvement of Superficial and Deep Cutaneous Microcirculation Due to Axillary Plexus Anesthesia Impaired by Smoking

Background: Understanding microvascular physiology is key to any reconstructive procedure. Current concepts in anesthesia increasingly involve regional peripheral nerve blockade during microvascular reconstructive procedures. Whereas favorable effects on perfusion due to these techniques have been reported earlier, little evidence focusing on its effects in most peripheral vascular compartments is available. Methods: A total of 30 patients who were to receive axillary plexus blockade (APB) were included. Microcirculatory assessment of the dependent extremity was conducted utilizing combined laser-Doppler flowmetry and white light spectroscopy. Two probes (1–2 and 7–8 mm penetration depth) were used to assess changes in microcirculation. Results: APB resulted in significant changes to both superficial and deep cutaneous microcirculation. Changes in blood flow were most prominent in superficial layers with a maximum increase of +617% compared to baseline values. Significantly lower values of +292% were observed in deep measurements. Consecutively, a significant enhancement in tissue oxygen saturation was observed. Further analysis revealed a significant impairment of perfusion characteristics due to reported nicotine consumption (max Bf: +936% vs. +176%). Conclusion: Cutaneous microcirculation is strongly affected by APB, with significant differences regarding microvascular anatomy and vascular physiology. Smoking significantly diminishes the elicited improvements in perfusion. Our findings could influence reconstructive strategies as well as dependent perioperative anesthetic management.

The Effect of Botulinum Toxin on Flap Viability of the Posterior Thigh Perforator Flap in Rats

BACKGROUND

The use of perforator propeller flaps in lower limb reconstruction has increased recently. Many pharmacological agents are used to increase flap viability. Botulinum toxin has been used in various types of flaps in the literature. However, there is no study regarding the use of botulinum toxin in the lower limb propeller flaps. This study investigates the effect of botulinum toxin administration on flap survival for lower limb propeller flap in rats.

MATERIALS AND METHODS

The study included 20 male Wistar albino rats, divided into two groups with a flap rotation of 90° in group 1 and 180° in group 2. In both groups, botulinum toxin was administered to the right thigh and a physiological saline solution was applied to the left thigh. Five days later, flaps were elevated over the posterior aspect of the right and left thighs and inset after 90° and 180° rotation was performed. Histopathological, immunohistochemical, and necrosis area analyses were performed.

RESULTS

Necrosis area, edema, polymorphonuclear leukocyte infiltration, and necrosis were found to be higher on the left side of the groups, whereas epidermal thickness, collagen density, vascularization, and hair root density were found to be higher on the right side of the groups. No significant difference was found between the right posterior thighs in either group on any parameter other than vascularization. Histopathologically and immunochemically statistically significant differences were found between the two groups.

CONCLUSIONS

The present study found that botulinum toxin increases flap viability in lower limb perforator-based propeller flaps.

Optimizing remote ischemic conditioning (RIC) of cutaneous microcirculation in humans: Number of cycles and duration of acute effects

OBJECTIVE

Non-invasive Remote Ischemic Conditioning (RIC) offers an approach to reduce tissue damage in various organs/tissues. Besides attenuation of Ischemia-Reperfusion injury (I/R), beneficial effects on cutaneous microcirculation of free microsurgical flaps have been reported. Given the recency of this technique, there are considerable gaps in the current understanding of its mechanism of action. As a result, clinical transfer of RIC is prolongated in several fields. We aimed to optimize the RIC protocol by examination of different RIC-cycle numbers and its effect on changes of cutaneous microcirculation and duration.

METHODS

80 subjects were divided into groups (1, 3, 5, 7 RIC cycles). RIC was applied via an inflatable tourniquet. Cutaneous microcirculation was continuously assessed at the contralateral anterior lateral thigh utilizing a ©O2C-device continuously.

RESULTS

RIC caused significant and sustained changes in microcirculation. Four hours after completion of RIC, a maximum increase of +80.8% (CI 1.395-2.221) in blood flow and +23.5% (CI 1.098-1.372) in tissue oxygen saturation was measured (three-cycle group). A higher number of applied cycles was accompanied with significant higher mean pain.

CONCLUSION

Acute improvement of cutaneous microcirculation due to RIC lasted for at least 4 h after completion of the RIC-protocol. Dose-dependent effects of RIC are likely. With regard to the increase in pain, we recommend a RIC protocol of 3 cycles for future clinical application.

Lipoxin A4 protects rat skin flaps against ischemia-reperfusion injury through inhibiting cell apoptosis and inflammatory response induced by endoplasmic reticulum stress

Background

The ischemia-reperfusion (I/R) injury of skin flap is a complex pathophysiological process involving many cells and factors. Although endoplasmic reticulum (ER) stress-induced cell apoptosis and inflammatory response are of immense importance in the skin flap ischemia, the treatment for I/R injury induced by ER stress is barely reported.

Methods

Healthy male Wister rats were randomly divided into three groups: sham-operated group, I/R model group and I/R + LXA4 group. I/R-induced injury in skin flaps with or without pre-treatment of Lipoxin A4 (LXA4, 100 µg/kg) was tested by using HE and TUNEL staining. Related factors associated with oxidative stress, apoptosis, inflammatory response, and ER stress were tested by ELISA, biochemical assay, and western blotting, respectively.

Results

Our results showed that LXA4 treatment significantly promotes skin flap survival and attenuates I/R injury by inhibiting oxidative stress, apoptosis, and inflammatory factor release, evidenced by the decreased expression of malondialdehyde (MDA), lactate dehydrogenase (LDH), NF-κBp65, tumor necrosis factor α (TNF-α), ET, active Caspase-3 and Bax and up-regulated superoxide dismutase (SOD), glutathione (GSH) level and Bcl-2 expression. Moreover, LXA4 treatment also reverses the increased expression of GRP78, p-PERK, p-eIF2α, ATF4, and CHOP induced by I/R injury.

Conclusions

In conclusion, we showed that ER stress causes cell apoptosis and inflammatory response, resulting in the skin flaps injury. LXA4 exhibits a protective effect on skin flaps against I/R injury through the inhibition of ER stress.

Does ischemic preconditioning increase flap survival by ADORA2B receptor activation?

BACKGROUND

Ischemic preconditioning (IPC) is defined as raising tolerance to subsequent ischemic stress by exposing tissues to sub-lethal ischemia. Although many candidates have been suggested, recent studies have clearly demonstrated that adenosine-mediated ADORA2B receptor (ADORA2BR) activation is the main mechanism involved in IPC. While the tissue-protective role of this mechanism has been demonstrated in different ischemia/reperfusion (I/R) models, its role in flap surgery-derived I/R damage has not to date been investigated.

OBJECTIVE

To investigate the role of adenosine and ADORA2BR activation in IPC-mediated tissue protection in an epigastric flap model.

METHODS

Animals were divided into five main groups, all of which were then divided into two subgroups depending on whether or not they were exposed to IPC before the I/R procedure, which consisted of 6 hours of ischemia and 6 days of reperfusion. No drugs were administered in Group 1 (the control group). Animals in Group 2 were pretreated with CD73-inhibitor before IPC application or the ischemic period. Animals in Group 3 were pretreated with adenosine. Animals in Group 4 were pretreated with an ADORA2BR antagonist, and those in Group 5 with an ADORA2BR agonist. After 6 days of reperfusion, tissue survival was evaluated via histological and macroscopic analysis.

RESULTS

IPC application significantly enhanced CD73 expressions and adenosine concentrations (p < 0.01). Flap survivals were increased by IPC in Group 1 (p < 0.05). However, CD73 inhibition blocked this increase (Group 2). In Group 3, adenosine improved flap survival even in the absence of IPC (p < 0.01). While an ADORA2BR antagonist attenuated the tissue-protective effect of IPC (p < 0.01), the ADORA2BR agonist improved flap survival by mimicking IPC in groups 4 and 5.

CONCLUSION

These results provide pharmacological evidence for a contribution of CD73 enzyme-dependent adenosine generation and signaling through ADORA2BR to IPC-mediated tissue protection. They also suggest for the first time that ADORA2BR agonists may be used as a potential preventive therapy against I/R injury in flap surgeries.

Transplantation of a latissimus dorsi flap after nearly 6 hr of extracorporal perfusion: A case report

Prolonged ischemia of tissues inevitably leads to their necrosis. This is especially relevant in the case of transplantation or replantation. In such situations, reperfusion in a timely manner might not be possible due to transportation times or other unforeseen complications. Therefore, a readily available and simple method to oxygenate the tissue and thus widen the time frame to reperfusion seems desirable. Here, we present the case of extracorporal perfusion of a latissimus dorsi (LD) flap that was successfully transplanted after nearly 6 hr of ischemia. A 41-year-old patient suffered multiple injuries including complete severance of the popliteal artery requiring emergency bypass. After stabilization of the patient and subsequent debridement, a LD flap was performed for soft tissue coverage. However, there was an acute occlusion of the bypass during flap inset. To salvage the free flap, a one-way extracorporal perfusion of the flap with heparinized isotonic saline solution was performed for a total of 5 hr and 47 min. The flap survived with minimal tip necrosis. This case report describes the application of a simple extracorporal perfusion technique for salvage of a free flap over a prolonged ischemia time and discusses the relevant literature. Due to its ease and quickness of application as well as ubiquitous availability, it might serve as a valuable tool in cases of acute problems with the recipient vessels or other incidents where several hours of ischemia time are to be anticipated.

[Hyperspectral imaging for postoperative flap monitoring of pedicled flaps]

BACKGROUND

Since pedicle flaps were first described by the Indian physician Sushruta Samhita in the 6th century B. C., they have become an integral part of reconstructive surgery. As more and more research has been conducted into the underlying physical principles, flap monitoring has developed steadily in the last few decades. Hyperspectral Imaging (HSI) is a new quantitative measuring method for assessing the perfusion of the underlying tissue.

OBJECTIVE

This study aims to evaluate HSI as a monitoring method for pedicle flaps.

PATIENTS AND METHODS

In 16 patients who had undergone reconstructive surgery, oxygen saturation, haemoglobin and water concentration of the locoregional flap, necrotic flap areas as well as intact skin were measured on postoperative days 1 to 7. Subsequently, the data were statistically described and graphically illustrated.

RESULTS

HSI revealed increased haemoglobin concentration and decreased oxygen and water concentration in necrotic flap areas compared with the monitor island and healthy skin. The distribution of the values collected from the vital skin areas and the monitor island was almost identical.

CONCLUSION

HSI allows for safe, immediate, non-contact measurement of tissue perfusion of transferred tissue areas in patients after pedicle flap surgery. The use of HSI may improve postoperative flap monitoring.

Preconditioning with Foam-mediated External Suction on Flap Microvasculature and Perfusion in a Rodent Model

Foam-mediated external suction (FMES) has previously shown to improve tissue microcirculation. We hypothesized that preconditioning fasciocutaneous perforator flaps with FMES would augment perfusion and demonstrate greater capillary recruitment.

Thermal Preconditioning for Surgery: A Systematic Review

BACKGROUND

Optimising patients pre-operatively reduces the chance of complications. This may be achieved by preconditioning. Thermal preconditioning refers to the supraphysiological heating of organisms or specific organs prior to an environmental insult. This review explores the current application and efficacy of thermal preconditioning for surgery.

METHODS

A comprehensive search of Medline (via PubMed), Embase and the Cochrane library was performed. Only articles evaluating the use of supraphysiological heating prior to a surgical intervention were included. Qualitative syntheses of data were undertaken due to the heterogeneity of the studies. The quality of each article was appraised using risk of bias tools (Cochrane and SYRCLE).

RESULTS

The primary literature search returned 3175 articles. After screening and reviewing reference lists, 28 papers met the inclusion criteria. The majority of studies were performed in animals, with only three clinical trials. Although there was broad coverage of different surgical techniques, flap transfer was the most commonly performed procedure. Most studies demonstrated a beneficial effect of thermal preconditioning, ranging from increased joint mobility to improved flap or organ transplant survival rates. The quality of evidence was variable, with experimental animal studies limited by a lack of methodological detail.

CONCLUSIONS

Thermal preconditioning for surgery has been primarily investigated using animal models. A beneficial effect has been demonstrated in most cases, across specialties ranging from plastic to general surgery. Future studies should aim to assess the clinical significance through large multicentre randomised controlled trials.

Rip 1-dependent endothelial necroptosis participates in ischemia-reperfusion injury of mouse flap

BACKGROUND

Ischemia reperfusion injury plays an important role in free flap necrosis. However, the detailed mechanism is not clear, and effective methods for improving the survival rate of skin flap are still lacking.

OBJECTIVE

To investigate the regulation and functional link between necroptosis and ischemia-reperfusion injury of mouse flap.

METHODS

We established a mouse ischemia-reperfusion injury flap model and a cell Oxygen Glucose Deprivation (OGD) model intervened with Necrostatin-1. The mouse flap tissues were harvested in vivo for histological immunofluorescence analysis and western blotting analyses. The HUVECs cells with various treatments in vitro were assessed by using Transwell assay, tube formation assay, cell counting kit-8 analysis and flow cytometry. A Rip3-knockout cell line and a TNFR1-knockout cell line were generated from HUVEC cells using the CRISPR-Cas9 technology and were subsequently used to explore the related mechanisms.

RESULTS

The expression of p-Rip3 is positive in both mouse and cell culture models. When necroptosis is completely or partially inhibited in vivo, damaged tissues are repaired with better efficiency. The cells treated with Necrostatin-1 in vitro exhibit faster migration, proliferation and better tube formation. Deficiency of TNFR1 can block the necroptosis pathway by blocking the phosphorylation of Rip3 in HUVEC OGD/ROG model. Meanwhile, the levels of APJ, HIF-1α, and VEGF are reduced when necroptosis is inhibited by Necrostatin-1.

CONCLUSION

TNFR1 mediates Rip1/Rip3 in ischemia-reperfusion injury. Inhibition of necroptosis attenuates the ischemia-reperfusion injury of flap and may enhance hypoxic tolerance of HUVECs and vascular homeostasis through regulation of the HIF-1α signaling pathways.

The role of pedicled abdominal flaps in hand and forearm composite tissue injuries: Results of technical refinements for safe harvest

We evaluated the outcome of new technical refinements in abdominal flap coverage of major defects in upper limb for its reliability and safety. 68 patients were assessed for indications, additional procedures, complications and DASH questionnaire evaluation at the end of a year. The mean size of flap was 56 cm² (range 6-250 cm²). Median DASH score was 11.5 (range: 0-63). Hand stiffness was observed in 39% of patients. However, this was absent in whom prophylactic pinning of metacarpophalangeal joints were done in James position. Abdominal flaps give satisfactory results in hand injuries. Competent hand therapy program is essential to get best results.

Allogenic endothelial progenitor cell transplantation increases flap survival through an upregulation of eNOs and VEGF on venous flap survival in rabbits

BACKGROUND

Endothelial progenitor cells (EPCs) are one type of bone marrow hematopoietic stromal cells which play a vital role in neovascularization and tissue repair. In this study, we investigated whether EPCs promote flap survival in a rabbit venous model.

MATERIALS AND METHODS

EPCs were customized from CHI Scientific, Inc, China. Thirty-six rabbits were randomly assigned to either the sham group (n = 12), the control group (n = 12) or the EPC transplantation group (n = 12). A 10 × 6 cm venous flap was created on the rabbit abdomen. Both the EPC transplantation and control groups had the same volume of EPCs-PBS (phosphate buffered saline) and PBS on postoperative day 1. Flap survival, blood flow, histopathology, expression of endothelial nitric oxide synthase (eNOs) and Vascular Endothelial Growth Factor (VEGF) were detected on postoperative day 10.

RESULTS

Cellular immunofluorescence assay positively confirmed that the EPCs were undergoing differentiation. The survival rate of the flap in the EPC transplantation group was 58.4 ± 7.1%, which was significantly higher than that of the control group (4.8 ± 3.4%) (p<0.01). Histological examination revealed that the EPC transplantation group had higher microvessel density, fewer inflammatory cells, and a higher expression of eNOs and VEGF. Significantly increased blood flow perfusion was seen in the EPC transplantation group using laser Doppler imaging. The Western Blot technique revealed that the expression of eNOs and VEGF in the EPC transplantation group were both significantly higher than those in the control group.

CONCLUSION

This study demonstrated that EPC transplantation improved venous flap survival in rabbits. The present findings may provide insight into the promotion of venous flap survival in clinical practice in the future.

The Effect of Topical Vitamin A and E on Ischemic Random Skin Flap Survival

BACKGROUND

Ischemia of skin flaps is an important complication in reconstructive surgery. This study evaluated the efficacy of topical vitamins A and E on improving flap survival.

METHODS

Twenty-four white-albino male rats were randomly divided into two groups of treatment and control. Standard rectangular, distally based dorsal random pattern skin flap was elevated. Intra-peritoneal cephazoline was administered to prevent any unexpected infection. No pharmaceutical agent was administered for the control group, but pure vaseline ointment. In treatment group, vaseline plus vitamins A and E were administrated daily after surgery for 10 days. The rats were evaluated on the 10^th day after surgery for viable and necrotic portions of the flaps.

RESULTS

The mean values of necrosis in the flaps were 625±189.56 and 920.00±247.31 in the treatment and control groups, respectively. Vaseline plus vitamins increased flap survival significantly.

CONCLUSION

Topical vitamins A and E may be effective pharmaceutical agents to increase viability of random skin flaps in rats. They can be added to vasoactive topical agents to reach better results.

The Use of Botulinum Toxin in Flap Surgery: A Review of the Literature

Botulinum neurotoxin-A and botulinum neurotoxin-B have been shown to play a potential role in improving flap survival in animal models. The aim of this study is to review indications as well as to study injection timing, technique, and doses of botulinum neurotoxin-A and botulinum neurotoxin-B in animal models. Seventeen articles describe a total of 266 animals that underwent botulinum toxin injections before or during flap harvesting or vascular anastomosis procedure. All the studies demonstrated a beneficial effect of botulinum toxin administration in flap surgery or vascular anastomosis. Botulinum neurotoxin-A injection was shown to be a reliable approach in reducing vascular complications rate and increasing survival of flaps in animal models. The main conclusions drawn from the study include the following: perivascular injections targeting each vascular pedicle are preferred in cases of free flaps or axial flaps; subdermal injections are favorable in cases of random pattern skin flaps; and injections should be performed 7 days before flap elevation.

A randomised controlled feasibility trial to evaluate local heat preconditioning on wound healing after reconstructive breast surgery: the preHEAT trial

Objective

preHEAT was a randomised controlled feasibility trial to determine how best to measure skin necrosis in breast reconstruction to inform the design of a larger multicentre trial.

Background

Mastectomy skin flap necrosis (MSFN) is a serious complication resulting in prolonged wound healing. Local heat preconditioning of the MSF before surgery has been shown to reduce skin necrosis in immediate breast reconstruction patients (IBR).

Method

preHEAT was a single-centre, randomised control two-arm single-blind parallel arm feasibility trial of local heat preconditioning in breast cancer patients undergoing SSM and NSM at Guy’s and St Thomas’ Hospital, London, UK. All patients undergoing IBR above the age of 18 were included. Intervention patients heated breast skin to 43 °C in three, 30-min cycles interrupted by spontaneous cooling using hot water bottles. The primary aim was to compare measurement of skin necrosis using binary ‘yes/no’ assessment, the SKIN score, and wound area.

Results

One hundred forty-one patients were randomised over a 2-year period (71 heated group, 70 controls). There was near perfect agreement between assessors using the “yes/no” measurement of necrosis. The proportion of patients experiencing necrosis in controls was 35% (n = 23/66) in the heated 26% (n = 18/68]). In the control group, 17% (n = 4/23) patients experiencing necrosis required surgical intervention for necrosis compared to 11% (n = 2/18) in the heated group.

Conclusion

The binary outcome of MSFN “yes/no” is a suitable and reliable primary outcome measure of necrosis and was superior to the SKIN Score or necrosis area. The trial study design is feasible for a larger definitive trial.

Trial registration

ISRCTN15744669. Date of registration: 25/02/2018

Electronic supplementary material

The online version of this article (10.1186/s40814-019-0392-y) contains supplementary material, which is available to authorized users.

Ischemia-reperfusion injury in a rat microvascular skin free flap model: A histological, genetic, and blood flow study

Ischemia reperfusion injury is associated with tissue damage and inflammation, and is one of the main factors causing flap failure in reconstructive microsurgery. Although ischemia-reperfusion (I/R) injury is a well-studied aspect of flap survival, its biological mechanisms remain to be elucidated. To better understand the biological processes of ischemia reperfusion injury, and to develop further therapeutic strategies, the main objective of this study was to identify the gene expression pattern and histological changes in an I/R injury animal model. Fourteen rats (n = 7/group) were randomly divided into control or ischemia-reperfusion group (8 hours of ischemia). Microsurgical anastomoses were objectively assessed using transit-time-ultrasound technology. Seven days after surgery, flap survival was evaluated and tissue samples were harvested for anatomopathological and gene-expression analyses.The I/R injury reduced the survival of free flaps and histological analyses revealed a subcutaneous edema together with an inflammatory infiltrate. Interestingly, the Arginase 1 expression level as well as the ratio of Arginase 1/Nitric oxide synthase 2 showed a significant increase in the I/R group. In summary, here we describe a well-characterized I/R animal model that may serve to evaluate therapeutic agents under reproducible and controlled conditions. Moreover, this model could be especially useful for the evaluation of arginase inhibitors and different compounds of potential interest in reconstructive microsurgery.

Necrostatin-1 protects against ischemia/reperfusion injury by inhibiting receptor-interacting protein 1 in a rat flap model

INTRODUCTION

The failure of reconstructive surgeries remains a challenge for plastic surgeons. Ischemia reperfusion (I/R) injury is considered to be one of the major problems in flap surgery. Necroptosis is a recently discovered and caspase-3-independent programed necrosis. Necrostatin-1 (Nec-1) is a specific inhibitor of necroptosis. Reports indicate that Nec-1 provides protection in ischemic models, such as brain, kidney, and heart. The aim of this study is to investigate the influence of Nec-1 on the I/R process in rat abdominal skin flaps.

METHODS

Twenty male Sprague-Dawley rats, weighing 280-320 g, were randomly divided into three groups. The extended epigastric skin flap (6 cm × 9 cm) of rats was used. Three hours of complete ischemia was performed using a clamp, and the clamp was then removed to reperfusion the flap. Twenty-four hours after the onset of the reperfusion, the rats were assessed for flap survival and perfusion analysis. One sample (1 cm × 1 cm) was taken for H&E, TUNEL, electron microscopy, IHC staining for RIP-1, and ELISA analysis for caspase-3 activity.

RESULTS

Compared to the CTL group, the flap in the Nec-1 group showed a higher survival rate and better blood perfusion. In histological observation, skin flap in the Nec-1 group showed less inflammatory infiltration than the CTL group. The AI in the CTL group was higher than that in the Nec-1 group and showed typical morphological changes of apoptotic cells. In IHC study, RIP-1 expression was higher in the CTL group. But there was no significant difference between the two groups in caspase-3 activity detection.

CONCLUSION

Nec-1 has a protective effect against I/R injury through the inhibition of RIP-1 on the skin flap model; this makes it a promising novel strategy in clinical setting.

Salvianolic Acid B Promotes the Survival of Random-Pattern Skin Flaps in Rats by Inducing Autophagy

Random-pattern skin flap transplantation is frequently applied in plastic and reconstructive surgery. However, the distal part of the flap often suffers necrosis due to ischemia. In this study, the effects of salvianolic acid B (Sal B) on flap survival were evaluated, and the underlying mechanisms were investigated. Sal B improved the survival area, reduced tissue edema, and increased the number of microvessels in skin flaps after 7 days, whereas an autophagy inhibitor (3-methyladenine) reversed the Sal B-induced increase in flap viability. In addition, Sal B stimulated angiogenesis, inhibited apoptosis, reduced oxidative stress, and upregulated autophagy in areas of ischemia. Moreover, the effects of Sal B on angiogenesis, apoptosis, and oxidative stress were reversed by autophagy inhibition. Overall, our findings suggest that Sal B has pro-angiogenesis, anti-apoptosis, and anti-oxidative stress effects by stimulating autophagy, which enhances the survival of random-pattern skin flaps.

Quantitative impact analysis of remote ischemic conditioning and capsaicin application on human skin microcirculation

BACKGROUND

Improvement of skin microcirculation would be beneficial in transplanted tissues and thus, there is a demand for effective, reliable and harmless angiogenic treatments. The aim of this study was to assess the effect of capsaicin application (CA), the remote effect of capsaicin application (REC), the impact of remote ischemic conditioning (RIC), and the impact of combined remote ischemic conditioning with capsaicin application (Comb) on human skin microcirculation.

METHODS

Perfusion changes were assessed using a laser Doppler device (easyLDI, Aimago Lausanne). 30 healthy volunteers were enrolled and divided into two groups: 1) CA and REC: perfusion was assessed on both forearms after application of capsaicin cream on one forearm with an exposure time of 40 minutes. 2) RIC and Comb: perfusion of one forearm was assessed after four cycles of 5 min blood occlusion and 5 min reperfusion using a tourniquet on the contralateral upper arm and application of capsaicin on the ipsilateral forearm. Baseline skin perfusion measurements of both forearms were carried out initially and were used as intra-individual reference.

RESULTS

1) Skin perfusion significantly increased after capsaicin application (CA = +328.3% , p > 0.05). There was no remote skin perfusion change due to capsaicin (REC). 2) RIC significantly improves skin perfusion (RIC = +20.0% , p < 0.05). The combination of RIC and CA does not improve skin perfusion compared to CA alone (Comb).

CONCLUSIONS

The conditioning techniques RIC and CA showed a significant increase in human skin perfusion, CA being superior to RIC. However, the combination of CA and RIC showed no additional improvement potential as compared to CA alone. Furthermore, a remote effect of capsaicin application could not be demonstrated. These results encourage to analyze if the conditioning treatments are also beneficial for transplanted tissue survival.

Effect of Human Placental Extract Treatment on Random-Pattern Skin Flap Survival in Rats

Background: Human placental extract (HPE), prepared from the placentas of healthy, postpartum females, displays various physiological activities, including antioxidative properties. In this study, a dorsal skin flap model was used to investigate the effect of HPE on flap viability in rats. Materials and methods: Forty male Sprague-Dawley rats underwent random-pattern skin flap surgeries. The animals were randomly divided among a control group and three treatment groups (localized injection (LI), 10 mg/kg/d localized HPE injections; low-dose treatment (LT), 10 mg/kg/d systemic HPE injections; high-dose treatment (HT), 40 mg/kg/d systemic HPE injections). Surviving skin flap areas were measured 7 days after surgery and tissue samples were stained with hematoxylin and eosin; vascular endothelial growth factor expression was determined immunohistochemically. To evaluate the antioxidant and antiapoptotic effects of HPE, malondialdehyde, glutathione peroxidase, and caspase-3 levels were examined. Results: Seven days after surgery, HPE-treated animals had significantly reduced necrotic areas, rats receiving the highest HPE dose demonstrated the greatest flap survival. In the HPE groups, the histopathological scores were lower than for the control group. Immunohistochemistry showed markedly more numerous vascular endothelial growth factor-positive cells in the HT group than in the C group. Malondialdehyde levels were significantly lower and glutathione peroxidase levels were higher in the HT group than in the C group. HPE treatment significantly inhibited apoptosis by lowering caspase-3 activity. Conclusions: HPE treatment yielded positive effects on flap survival, due to its antioxidant and antiapoptotic properties. These results suggest a new therapeutic approach for enhancing flap viability and accelerating wound repair.

The Effect of Ozonated Olive Oil on Neovascularizatıon in an Experimental Skin Flap Model

OBJECTIVE

Angiogenesis is an important factor for flap viability. It has been reported that ozonated oil contributed to improved neovascularization in an acute cutaneous wound healing model. This study was undertaken to evaluate the effect of ozonated olive oil on vascular endothelial growth factor (VEGF)-mediated neovascularization of skin flaps in rats.

STUDY DESIGN

A skin flap model was established in 21 rats and evaluated within 3 groups. No treatment was given to the rats in group 1. Olive oil and ozonated olive oil were topically applied (twice daily) to the flap surface for 7 days in groups 2 and 3, respectively. Immunohistochemical staining was performed to analyze the expressions of VEGF and CD34.

RESULTS

The mean numbers of VEGF- and CD34-positive staining microvascular structures were 8.86 (SD, 1.35) and 10.29 (SD, 1.80) in group 1, 15.00 (SD, 1.41) and 15.57 (SD, 1.72) in group 2, and 25.14 (SD, 2.41) and 25.00 (SD, 2.16) in group 3. The VEGF and CD34 expressions in group 3 were significantly higher than those in group 2 (P < .001). Their expressions in group 2 were significantly higher than those in group 1 (P < .001).

CONCLUSIONS

Both ozonated olive oil and olive oil improved neovascularization when they were topically applied on skin flaps. The effect of ozone was more prominent.

Dual Role of MiR-21-Mediated Signaling in HUVECs and Rat Surgical Flap under Normoxia and Hypoxia Condition

Restoring sufficient vascularity of the ischemia/hypoxia flap is always the critical issue in flap surgeries. In a previous studies microRNA-21 (miR-21) expression was upregulated after rat skin flap surgery. MiR-21 has been reported to be induced by hypoxia and the function of miR-21 involves in the process of angiogenesis. However, the precise regulatory mechanisms in miR-21-mediated pathways are still unclear. These issues were investigated via in vitro and in vivo experiments in this study. In human umbilical vein endothelial cells (HUVEC), the expression of hsa-miR-21-5p was induced after hypoxic culture and the induction of hsa-miR-21-5p was suppressed after sequential normoxic culture. Moreover, transfection of hsa-miR-21-5p mimic enhanced tube formation capacity in normoxia, but attenuated it in hypoxia. Furthermore, bioinformatic analysis suggested that SMAD7 was a predicted target of hsa-miR-21-5p. Our results demonstrated the effect of hsa-miR-21-5p was different on SMAD7 expression in normoxia and hypoxia. In rat skin flaps, blockage of miR-21-5p significantly increased angiogenesis via analysis of color laser Doppler imaging and repressed SMAD7 expression in ischemic skin tissue. Our study showed the opposite effect of miR-21-5p mediating angiogenesis in normoxia and hypoxia, providing important implications regarding the design of novel miRNA-based therapeutic strategies in flap surgeries.

Estradiol postconditioning relieves ischemia/reperfusion injury in axial skin flaps of rats, inhibits apoptosis and alters the MKP-1/ERK pathway

Previous studies have suggested that estradiol can reduce the ischemia/reperfusion (I/R) injury in skin flaps. However, the mechanism, particularly the signal pathways involved in this protective effect are not well established. In the current study, an I/R injury model was established in rats to explore the connection between estradiol protection during I/R injury and extracellular signal‑regulated kinase (ERK) signaling. Healthy male Wistar rats were divided into five groups (n=10): Control group (group I), I/R group (group II), saline group (group III), estradiol group (group IV) and inhibitor (PD‑98059) group (group V). The survival rate of the flap was compared between groups, morphological changes were observed by hematoxylin and eosin staining of sections, and terminal deoxynucleotidyl transferase dUTP nick end labeling was performed to identify apoptotic cells and determine the apoptotic index. To further investigate the mechanism, western blot analysis was performed to assess the protein level of ERK1/2, phospho‑ERK1/2, and mitogen‑activated protein kinase phosphatase 1 (MKP‑1). The results of the present study demonstrated that estradiol therapy can reduce I/R injury and decrease the apoptosis index in an axial skin flap model. The inhibitor of the ERK pathway (PD‑98059) partially abolished the effects of estradiol, which involve the phosphatase enzyme MKP‑1. Taken together, the findings of the present study indicate that estradiol may act by reducing the expression of MKP‑1, mediating the expression/activation changes of the ERK pathway and subsequently reduce the level of apoptosis and the I/R injury the axial flap. Estrogen may be used to mitigate the adverse reaction caused by ischemia‑reperfusion injury and effectively improve the survival rate and survival quality of free skin flap and improve patient prognosis.

Skin Perfusion Changes within 12 h after Axillary Plexus Block

Background/Purpose: An improvement of the blood flow would be beneficial in microvascular upper-extremity reconstruction and in digit replantation. In the present work, skin perfusion changes and their duration due to axillary plexus block were quantified. Methods: The peripheral blood flow of the upper extremities in 20 patients undergoing trapeziectomy under axillary plexus block was analyzed. Results: Laser Doppler spectrophotometry was used to measure perfusion factors over a 12-h period, with the contralateral hand acting as the control. Axillary plexus block produced a significant increase of peripheral oxygen saturation (117 ± 35% vs. control 93 ± 22%, p = 0.019), peripheral blood flow (220 ± 166% vs. 130 ± 77%, p = 0.037), and velocity (164 ± 58% vs. 117 ± 45%, p = 0.011). Conclusion: Axillary plexus block produces an improvement of peripheral tissue oxygen saturation of the upper extremities over the first 6 h after the inception of anesthesia. This suggests a potential benefit especially for critically perfused tissues.

Remote Ischemic Conditioning Improves Blood Flow and Oxygen Saturation in Pedicled and Free Surgical Flaps

BACKGROUND

Surgical flaps have become safe and reliable reconstructive tools, but total flap loss rates as high as 25 percent and partial flap loss rates as high as 36 percent have been reported due to insufficient perfusion. Therefore, a reliable, noninvasive, and effective way to improve the microcirculation of surgical flaps is desirable. The aim of this study was to assess the effect of remote ischemic conditioning on the microcirculation of pedicled and free surgical flaps.

METHODS

Thirty patients undergoing free (n = 20) and pedicled (n = 10) tissue transfer were included in this study. Remote ischemic conditioning was applied on the upper extremity for three cycles on postoperative days 1, 5, and 12. Blood flow, tissue oxygen saturation, and relative hemoglobin content were measured by means of a combination of laser Doppler and spectroscopy (O2C device) in the flap and the surrounding tissue. The relative increase compared with baseline measurements was assessed.

RESULTS

Blood flow increased significantly in controls on all 3 postoperative days (p < 0.05 for all). In free flaps, tissue oxygen saturation improved significantly on postoperative days 1 and 12 and blood flow improved significantly on postoperative days 5 and 12 (p < 0.05). In pedicled flaps, blood flow and tissue oxygen saturation increased on postoperative day12, but not significantly.

CONCLUSIONS

Remote ischemic conditioning is a safe, inexpensive, fast, and reliable method to improve the microcirculation of surgical flaps. Further research is warranted to see whether such an improvement translates into improved flap survival, but it is likely.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Contact Cooling of Random-Pattern Cutaneous Flaps: Does it Increase Necrosis?

BACKGROUND

Cooling after surgery reduces pain, swelling and ecchymosis. However, the fear of adverse effects of vasoconstriction caused by cooling may prevent its use when the skin is undermined extensively, for example, after rhytidectomy. The purpose of this study is to determine whether the contact cooling of random-pattern skin flaps increases the area of necrosis observed.

METHODS

Twenty-eight random-pattern skin flaps (4 × 10 cm) were raised on four pigs. Flaps were divided into three groups: control, intermittently cooled and continuously cooled. Pads connected to a ThermaZone cooling device delivered local hypothermia in the range of 4-6 °C for 24 h postoperatively. ImageJ software was used to calculate the area of necrosis on each flap on postoperative day 7, confirmed with histological analysis.

RESULTS

The average areas of necrosis observed were as follows: control (17.61 cm²; SD 5.23), intermittent cooling (15.65 cm²; SD 3.76) and continuous cooling (14.16 cm²; SD 3.91). An ANOVA revealed no statistically significant differences between the three interventions (p = 0.35).

CONCLUSIONS

Postoperative continuous or intermittent cooling does not increase the area of necrosis in random-pattern flaps. In fact, a trend was observed, demonstrating decreasing area of necrosis with increased periods of hypothermia.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors. www.springer.com/00266 .

Microvascular Fragment Transplantation Improves Rat Dorsal Skin Flap Survival

BACKGROUND

The development of flap necrosis distally remains a concern during microsurgical flap transfers because, at least in part, of decreased perfusion. Microvascular fragments (MVFs) are microvessels isolated from adipose tissue that are capable of improving tissue perfusion in a variety of tissue defects. The aim of this study was to determine whether the transplantation of MVFs in a dorsal rat skin flap model can improve flap survival.

METHODS

A 10 × 3 cm flap was raised in a cranial to caudal fashion on the dorsal side of 16 Lewis rats, with the caudal side remaining intact. The rats were equally divided into a treatment group (MVFs) and a control group (sterile saline). At the time of surgery, sterile saline with or without MVFs was injected directly into the flap. Microvessel density was determined after harvesting flap tissue by counting vessels that positively stained for Griffonia simplicifolia lectin I-isolectin B4. Laser Doppler was used to measure blood flow before and after surgery and 7 and 14 days later. Flap survival was evaluated 7 and 14 days after surgery by evaluating the percentage of viable tissue of the flap with photodigital planimetry.

RESULTS

Despite the lack of a significant difference in microvessel density and tissue perfusion, flap survival increased 6.4% (P < 0.05) in MVF-treated animals compared with controls.

CONCLUSIONS

The use of MVFs may be a means to improve flap survival. Future studies are required to delineate mechanisms whereby this occurs and to further optimize their application.