Indocyanine green videoangiography-assisted prediction of flap necrosis in the rat epigastric flap using the flow® 800 tool

Extrinsic Vascular Pathway Preservation Improves Survival in a Rat Three-Territory Flap Model Based on the Deep Circumflex Iliac Artery

BACKGROUND

Extended flaps are commonly applied for large defects. However, a postoperative flap necrosis incidence of 11% to 44% remains a major complication. Previous clinical studies have shown that maintaining the extrinsic vascular pathway (EVP) can increase the survival area of extended flaps. The authors hypothesized that preserving the EVP would improve flap survival by reducing blood resistance within the vascular territory.

METHODS

Twenty-four adult male Sprague-Dawley rats were used. Tissue samples were obtained from eight untreated rats as a baseline control. Three-territory flaps were elevated in the remaining 16 rats. The EVP was preserved or ligated. Flap perfusion was assessed immediately using indocyanine green angiography. Rats were euthanized on day 7. The flap survival area was measured using Adobe Photoshop. Hematoxylin and eosin staining, CD31 immunostaining, and Western blot analysis of vascular endothelial growth factor protein expression were used to quantitatively assess vasodilation and angiogenesis in choke zones.

RESULTS

Indocyanine green angiography revealed that blood could flow through the preserved EVP and perfuse the third vascular territory of the flap. EVP preservation significantly increased flap survival area (86.3%, 19.3% difference; P < 0.001), promoted vasodilation (5.0/choke zone, 3.0/choke zone difference; P = 0.013) and angiogenesis (29.3/mm 2 , 14.3/mm 2 difference; P = 0.002), and increased vascular endothelial growth factor expression (0.6, 0.2 difference; P = 0.067) in the second choke zone.

CONCLUSIONS

EVP preservation improves flap survival in this rat three-territory flap model. Further investigation in large-animal models is required for clinical translation.

CLINICAL RELEVANCE STATEMENT

Although further validation in large animal models and prospective clinical trials are necessary to verify the efficacy of the authors' hypothesis, their findings suggest that the EVP preservation procedure could provide an alternative for surgeons to create an extended flap in defect reconstruction.

The Autonomization Principle in Vascularized Flaps: An Alternative Strategy for Composite Tissue Scaffold In Vivo Revascularization

Autonomization is a physiological process allowing a flap to develop neo-vascularization from the reconstructed wound bed. This phenomenon has been used since the early application of flap surgeries but still remains poorly understood. Reconstructive strategies have greatly evolved since, and fasciocutaneous flaps have progressively replaced muscle-based reconstructions, ensuring better functional outcomes with great reliability. However, plastic surgeons still encounter challenges in complex cases where conventional flap reconstruction reaches its limitations. Furthermore, emerging bioengineering applications, such as decellularized scaffolds allowing a complex extracellular matrix to be repopulated with autologous cells, also face the complexity of revascularization. The objective of this article is to gather evidence of autonomization phenomena. A systematic review of flap autonomization is then performed to document the minimum delay allowing this process. Finally, past and potential applications in bio- and tissue-engineering approaches are discussed, highlighting the potential for in vivo revascularization of acellular scaffolds.

Preoperative Peroneal Artery Perforator Mapping Using Indocyanine Green Angiography: A Prospective Clinical Trial

BACKGROUND

Perforator imaging is a prerequisite in preoperative planning of the peroneal perforator flap and the fibula skin island. Although reports indicate that indocyanine green angiography assessment method might be advantageous over conventional ultrasound-based techniques (i.e., Doppler and color duplex), in practice, clear evidence is lacking. Thus, a comparative assessment of the utility of indocyanine green angiography and ultrasound-based techniques in the identification of suitable lower leg skin perforators was performed.

METHODS

A prospective clinical cohort study with a series of 12 consecutive patients was conducted to assess indocyanine green angiography, Doppler ultrasound, and color duplex ultrasound techniques for preoperative perforator detection in the lower leg before free fibula flap harvest. Anatomical dissection served as a reference. Parameters measured were perforator spatial distance to the reference (precision), operative time expenditure, and ease of device usage for assessment/outcomes.

RESULTS

This study included 12 patients, with a total of 27 perforators. Exhibition of technique sensitivity and positive predictive values were as follows: indocyanine green angiography, 93 percent and 100 percent; Doppler ultrasound, 82 percent and 82 percent; and color duplex ultrasound, 89 percent and 86 percent, respectively. With regard to the indocyanine green angiography technique, the distance to the actual perforator location was significantly shorter, which aided detection and lesser time expenditure during operation.

CONCLUSIONS

The indocyanine green angiography technique proved to have high precision, sensitivity, positive predictive value, and easy-to-use capabilities because of its exceptional spatial and temporal information, compared to the conventional, ultrasound-based techniques. Therefore, indocyanine green angiography is superior for preoperative perforator imaging of the lateral lower leg.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Diagnostic, II.

Hyperintensity of integrin-targeted fluorescence agent IntegriSense750 accurately predicts flap necrosis compared to Indocyanine green

BACKGROUND

Flap necrosis is a feared complication of reconstructive surgery. Current methods of prediction using Indocyanine green (ICG) lack specificity. IntegriSense750 is a fluorescence agent that binds sites of vascular remodeling. We hypothesized that IntegriSense750 better predicts flap compromise compared to ICG.

METHODS

Fifteen mice underwent lateral thoracic artery axial flap harvest. Mice received an injection of ICG (n = 7) or IntegriSense750 (n = 8) daily from postoperative days (POD) 0-3 and were imaged daily. Mean signal-to-background ratios quantified the change in fluorescence as necrosis progressed.

RESULTS

Mean signal-to-background ratio was significantly higher for IntegriSense750 compared to ICG on POD0 (1.47 ± 0.17 vs. 0.86 ± 0.21, p = 0.01) and daily through POD3 (2.12 ± 0.70 vs. 0.96 ± 0.29, p < 0.001).

CONCLUSIONS

IntegriSense750 demonstrates increased signal-to-background ratio at areas of flap distress compared to ICG which may increase identification of flap necrosis and improve patient outcomes.

Photoacoustic Microscopy Provides Early Prediction of Tissue Necrosis in Skin Avulsion Injuries

BACKGROUND

Skin avulsion injuries caused by high-energy traffic and machinery accidents are important topics in the field of repair and reconstruction. The injury generates a skin flap with uncertain vascular basis resulting in ischemic necrosis of the distal portion of the flap. Yet there is lack of reliable way for estimating the extent of blood supply in damaged tissue, which has limited the possibility of prompt surgical intervention. Recent studies have confirmed that photoacoustic microscopy imaging has a wide range of applications in the biomedical field owing to its good performance in angiography.

METHODS

In our study, we successfully surgically induced skin avulsion injury on mice hindlimbs. Then, we used this novel approach to image skin microcirculation and predict skin necrosis with impaired blood supply after injury in live mice.

RESULTS AND CONCLUSION

All skin tissues in the avulsed hindlimb flap group show different levels of necrosis at the end of the observation period. The "dark zone" with impaired microcirculation in PAM images, which continuously extends over time, was seen as a prediction of necrosis of skin tissue and at 60 min after surgery was similar to the area of clinical necrosis on postoperative day 7. All these indicate that photoacoustic microscopy imaging is a feasible, precise, high-resolution, non-invasive technique for early prediction of necrosis in skin avulsion injury, providing a promising tool for surgeons to manage the injury.

Effects of endothelial defects and venous interposition grafts on the acute incidence of thrombus formation within microvascular procedures

Endothelial defects (ED) and the usage of interposition vein grafts (IVG) are known risk factors for free flap failure. This experimental study aimed to compare both situations of thrombus formation and fluorescence angiographic behavior. Indocyanine green videoangiography (ICGVA) with the FLOW 800 tool was systematically performed in groups I = ED, II = IVG, and III = ED and IVG (each n = 11). ICGVA was able to detect thrombosis in five animals and safely ruled it out in 26 with two false-positive cases (sensitivity, specificity, and positive and negative predictive values were 100%, 90%, 62%, and 100%, respectively). The difference between visually and ICGVA-assisted ED measurements was significant (p = 0.04). The areas of thrombosis showed no significant difference. Moreover, ICGVA detected a decrease of all parameters at the ED area and/or within the IVG section in all groups. The presence of an endothelial defect had a higher impact on thrombus formation than the IVG usage. ICGVA is qualitatively able to detect endothelial defects and clinically evident thrombosis. However, the quantitative values are not yet attributable to one of the clinical scenarios that may jeopardize free flap transfer.

Indocyanine Green Angiography Predicts Tissue Necrosis More Accurately Than Thermal Imaging and Near-Infrared Spectroscopy in a Rat Perforator Flap Model

BACKGROUND

Clinical examination alone is neither sensitive nor specific for predicting flap necrosis, so several technologies, including indocyanine green angiography, thermal imaging (using the FLIR ONE), and near-infrared spectroscopy, have been developed to supplement perfusion assessment. This study aims to compare the accuracy of these three methods for intraoperatively predicting clinical flap necrosis in a rat perforator flap model. The authors hypothesized that near-infrared spectroscopy, assessing oxygenation rather than direct perfusion, would yield significantly different predictions.

METHODS

A 10 × 3-cm epigastric perforator flap was elevated in 14 adult male rats weighing 250 ± 50 g. Flap perfusion was assessed immediately after flap elevation using thermal imaging, near-infrared spectroscopy, and indocyanine green angiography. Measurements were correlated to the clinical endpoint and gold standard of flap necrosis on postoperative day 7.

RESULTS

All three technologies detected significant differences in perfusion along flap length (all p < 0.001), and were associated with significant differences in the odds of developing flap necrosis (all p < 0.001). The areas under the receiver operating characteristic curves were 0.948 for indocyanine green angiography as an absolute value, 0.873 for relative changes with thermal imaging, and 0.792 for tissue oxygenation. The sensitivity, specificity, and accuracy for indocyanine green angiography measured as an absolute value were the highest at 97.8, 87.5, and 92 percent, respectively.

CONCLUSIONS

Indocyanine green angiography most accurately predicted flap necrosis in this study; however, tissue oximetry and thermal imaging were also capable of predicting necrosis and represented potentially less expensive or more readily available alternatives for objective perfusion assessment. Additional research can further delineate their roles and cost-efficacy in clinical practice.

Role of Ultrahigh Frequency Ultrasound in Evaluating Experimental Flaps

BACKGROUND

 Experimental flap follow-up needs faster, safer, and less invasive techniques that can be easily correlated to clinical procedures. For this reason, we aimed to test the role of ultrahigh frequency ultrasound in follow-up of flap viability. Further on, we aimed to analyze if the chimeric groin flap can be mobilized in a sandwiched position without affecting its vascular supply by twisting its pedicle.

METHODS

 A total of 12 male Wistar rats, split into three groups, were used. Group A (n = 4) had the chimeric groin flap repositioned in a sandwich position on the anterior abdominal wall and underwent ultrahigh frequency ultrasound follow-up at days 10 and 14. Group B (n = 4) also had the flaps sandwiched, however, at day 14 the vascularity of flaps was proven by infusion of nontargeted ultrasound contrast agents, after which flaps were sent for histological analysis. Group C (C1 n = 2, C2 n = 2) was the control group. In C1 the chimeric groin flap was harvested and sent for histology on day 0, acting as a histological benchmark of flap viability, and in C2 the chimeric groin flap was re-sutured in its anatomical position and after 14 days, flaps were harvested and sent for histological analysis, acting as a direct control for Group B.

RESULTS

 Ultrasound showed constant vascular flow in both adipose and skin flaps in the sandwiched position. Microbubble study showed diffuse perfusion within flaps. Ultrasound measurements of flow velocity, flap volume, and percentage of vascularity showed a decrease in flap volume and increase in vascularity over 14 days. Histology showed similar viability in both groups.

CONCLUSION

 Ultrahigh frequency ultrasound may be a valuable tool for postoperative flap assessment, while the chimeric flap can be moved freely in a sandwich position making it suitable for adding tissue substitutes within its components.

Comparison between Different Perforator Imaging Modalities for the Anterolateral Thigh Perforator Flap Transfer: A Prospective Study

BACKGROUND

 Perforator imaging is routinely performed before perforator flap harvest. Hand-held Doppler (hhD) and color duplex ultrasonography (CDU) are currently the most popular radiation-free methods for this purpose that can be applied by the surgeon alone. The aim of this study was to compare the accuracy, reliability, and feasibility of hhD and CDU with indocyanine green angiography (ICGA) in the anterolateral thigh perforator flap (ALTPF).

METHODS

 All consecutive ALTPF procedures between May 2017 and April 2018 were included in this prospective study. The perforators were visualized by three investigators independently and randomized, applying hhD, CDU, and ICGA. The presence and the distance to the identified perforator were registered. Further, body mass index (BMI), American Society of Anesthesiologists-status, and the patient's history regarding smoking, alcohol use, and diabetes mellitus were registered alongside gender and age to analyze possible confounders.

RESULTS

 A total of 12 patients were enrolled with a median age of 67 (52-87) years. In total, 30 perforators were detected intraoperatively as well as with the ICGA. The latter visualized the perforators significantly more precisely than hhD and CDU (p < 0.001 and p = 0.001). The sensitivity and positive predictive value were 67 and 62% for hhD, 73 and 64% for CDU, and 100 and 100% for ICGA, respectively.

CONCLUSION

 According to this study, ICGA visualized perforators more accurately than the standard methods hhD and CDU. Further, it was associated with the highest sensitivity and positive predictive value. ICGA consistently delivered excellent results, whereas hhD and CDU showed variability.

A comparative analysis using flowmeter, laser-Doppler |spectrophotometry, and indocyanine green-videoangiography for detection of vascular stenosis in free flaps

The effects of gradual vascular occlusion on the blood supply of perfused areas are poorly described. Information relating to the comparison of flap monitoring techniques is lacking. Varying stenotic conditions (0%, 25%, 50%, 75% and 100%) were generated on purpose at the A. and V. femoralis in the rat model. Analyses included flowmeter, simultaneous laser-Doppler flowmetry and tissue spectrophotometry (O2C) and indocyanine green- (ICG-) videoangiography with integrated FLOW 800 tool. A Random Forests prediction model was used to analyse the importance of each method to diagnose the stenotic conditions. The ability to discriminate and to accurately estimate the probability of stenosis was assessed by Receiver Operating Characteristic (ROC) curves and calibration plots. Blood flow changes for all modalities were described in detail. Flowmeter displayed earliest a linear decrease as a result of increasing stenosis. A stenosis of 50% degrees was most difficult to detect correctly. The combination of flowmeter and ICG-videoangiography showed high diagnostic power for each stenotic situation (area under the ROC > 0.79). Flowmeter and ICG-videoangiography showed to be most relevant in detection of varying stenotic conditions and may change the clinical outcome. The O2C showed less effect on varying stenotic situations as the only surface monitoring device.

Evaluation of perfusion by near-infrared fluorescence imaging in late pedicle obstruction of a parascapular flap to the lower extremity: A case report

Late free flap failures due to pedicle obstruction are rare adverse events. The purpose of this report is to present a case in which the near-infrared indocyanine green video angiography (ICG-NIR-VA) was used to evaluate the perfusion in a compromised fasciocutaneous flap in the late postoperative period. A 55-year-old male patient, who initially suffered from an open tibial fracture, developed concurrent osteomyelitis with fistulae of the proximal tibia requiring excision. Reconstruction was achieved using a parascapular flap of 25 × 8 cm, anastomosed to an arterio-venous (AV) Loop in the adductor canal. On the 2nd postoperative day the patient developed a thrombosis of the AV-Loop. After thrombectomy, the postoperative course was uneventful. Seven weeks postoperatively the patient presented with a mottled, partially bluish and cold flap. Anticoagulation prophylaxis was stopped 2 days earlier. Angiography confirmed a thrombus in the arterial pedicle leading to flap ischemia. Near infrared guided fluorescence imaging revealed a delayed recapillarization of the proximal part of the flap closest to the vascular pedicle, albeit flap overall perfusion remained intact. Thus, no surgical intervention was undertaken. However, anticoagulation and prostaglandin therapy was initiated and the flap was salvaged. Genetic analysis uncovered a polymorphism in the prothrombin genes. The flap remained viable and without further complications until the last follow-up visit at 36 weeks after microsurgical reconstruction. The patient was fully mobilized with complete return to function. Near-infrared guided fluorescence imaging may be a viable tool for the assessment of late fasciocutaneous free flap complications and guide the decision-making process.

Detection of thrombosis in microvessels with indocyanine green videoangiography

Atherosclerosis is a systemic condition that is responsible for many diseases, and becomes a problem in cases where plaques form at several sites. The formation of a thrombotic embolus may jeopardise vascular operations, including microvascular anastomoses in replantation procedures or free tissue transfers. A mobile imaging tool for the detection of thrombosis preoperatively or intraoperatively would be valuable. An intimal injury, simulating removal of atherosclerotic plaques, was made microsurgically in 60 rat aortas, and results were analysed macroscopically, histologically, and with intraoperative indocyanine green (ICG) videoangiography immediately postoperatively. The Spearman and Pearson correlation tests were used to compare the three techniques. The sensitivity and specificity of ICG videoangiography was calculated in relation to both macroscopic and histological results. Detection of thrombosis was possible in 25 cases, and in 18 cases no thrombosis was correctly diagnosed by all methods used. In 31 of 60 specimens formation of thrombus was detected histologically, and in 29 of 60 examinations it was detected clinically, which yielded a correlation of 93.5% between the two examinations. Macroscopic analysis correlated better with ICG videoangiography (sensitivity 86.2% and specificity 64.5%) than histological observations (sensitivity 80.6% and specificity 62.1%). There was a significant correlation among all comparisons (each p≤0.001) with correlation indexes of 0.94, 0.52, and 0.44 for macroscopic/histological, clinical/ICG videoangiographic, and ICG videoangiographic/histological results, respectively. Our results show that ICG videoangiography is an important method for the detection of formation of acute thrombi and may be an important tool in vascular procedures.

Multimodal analysis using flowmeter analysis, laser-Doppler spectrophotometry, and indocyanine green videoangiography for the detection of venous compromise in flaps in rats

Venous congestion results in tissue damage and remains the most common failure of free microvascular transfer if it is not recognized early. The purpose of this experimental study was to evaluate venous congestion and describe the findings with two different monitoring tools. A standardized epigastric flap was raised, and total occlusion of the draining vein was temporarily applied for 4, 5, 6, or 7 h. Blood flow measurements, including laser-Doppler flowmetry, and tissue spectrophotometry (O2C) and indocyanine green (ICG) videoangiography using the FLOW^® 800 tool, were performed systematically after each surgical step, an interval of venous occlusion, and 1 week of clinical observation. Both monitoring tools were capable of detecting acute venous occlusion. ICG videoangiography data showed a significant decrease in the first and second maximum, and the area under the curve, during venous occlusion, whereas hemoglobin levels in the O2C analysis remained stable. Changes in fluorescence values in border areas of the flap correlated significantly with the incidence of necrosis. O2C data later showed significant correlation with the area of necrosis, and more individual changes during flap monitoring. ICG videoangiography might therefore be useful in the prediction of flap necrosis in critical areas of perfusion.

Vascular architecture in free flaps: Analysis of vessel morphology and morphometry in murine free flaps

The aim of this study was to analyze the development of vascular architecture as well as vascular morphometry and morphology of anastomosed microvascular free flaps. Free pectoral skin flaps were raised in 25 rats and anastomosed to the femoral vessels in the groin region. CD31 immunohistology was performed after 3, 7 and 12 d (each 5 animals each) to analyze microvessel density (MVD), microvessel area (MVA) and microvessel size (MVS). Microvascular corrosion casting was performed after 7 and 12 d (5 animals each) to analyze vessel diameter (VD), intervascular distance (IVD), interbranching distance (IBD), and branching angle (BA). Further on, sprout and pillar density as hallmarks of sprouting and intussusceptive angiogenesis were analyzed. Pectoral skin isles from the contralateral side served as controls. A significantly increased MVD was found after 7 and 12 d (p each <0.001). MVA was significantly increased after 3, 7 and 12 d (p each <0.001) and a significantly increased MVS was analyzed after 3 and 7 d (p each <0.001). VD and IVD were significantly increased after 7 and 12 d (p each <0.001). For IBD, a significantly increase was measured after 7 d (p < 0.001). For IBA, sprout and pillar density, no significant differences were found (p each ≥0.05). Significant changes in the vascular architecture of free flaps after successful microvascular anastomosis were seen. Since there was no evidence for sprout and pillar formation within the free flaps, the increased MVD and flap revascularization might be induced by the receiving site.

[Progress of monitoring methods and preventions of disorder of blood supplying of expanded flaps]

Objective

To summarize the monitoring methods and preventions of the disorder of blood supplying of expanded flaps, so as to provide some references for improving the survival of expanded flaps.

Methods

The domestic and abroad related literature about the disorder of blood supplying of expanded flaps was reviewed and analyzed.

Results

Handheld Doppler, digital subtraction angiography, computer tomographic angiography, magnetic resonance angiography, and fluorescein angiography can be used as reliable preoperative imaging methods in designing expanded flaps with rich blood supply. Several techniques can be used for monitoring the blood supply of expanded flaps during the early postoperative period including traditional monitoring via physical examination, monitoring via dynamic infrared thermography, near-infrared spectroscopy tissue oximeter, external and implantable Doppler, and more recently developed diffuse correlation spectroscopy. Surgical delay, bloodletting, leech therapy, hyperbaric oxygen, and so on can decrease the risk of necrosis in expanded flaps.

Conclusion

The survival of expanded flap is influenced by many factors. Preoperative design by using handheld Doppler and new imaging technology and postoperative early detection of blood supply can provide references of timely intervention, so that ischemic necrosis of the flaps can be reduced, and the success rate of surgery can be improved.

Role of Indocyanine Green in Fluorescence Imaging with Near-Infrared Light to Identify Sentinel Lymph Nodes, Lymphatic Vessels and Pathways Prior to Surgery - A Critical Evaluation of Options

Modern surgical strategies aim to reduce trauma by using functional imaging to improve surgical outcomes. This reviews considers and evaluates the importance of the fluorescent dye indocyanine green (ICG) to visualize lymph nodes, lymphatic pathways and vessels and tissue borders in an interdisciplinary setting. The work is based on a selective search of the literature in PubMed, Scopus, and Google Scholar and the authors' own clinical experience. Because of its simple, radiation-free and uncomplicated application, ICG has become an important clinical indicator in recent years. In oncologic surgery ICG is used extensively to identify sentinel lymph nodes with promising results. In some studies, the detection rates with ICG have been better than the rates obtained with established procedures. When ICG is used for visualization and the quantification of tissue perfusion, it can lead to fewer cases of anastomotic insufficiency or transplant necrosis. The use of ICG for the imaging of organ borders, flap plasty borders and postoperative vascularization has also been scientifically evaluated. Combining the easily applied ICG dye with technical options for intraoperative and interventional visualization has the potential to create new functional imaging procedures which, in future, could expand or even replace existing established surgical techniques, particularly the techniques used for sentinel lymph node and anastomosis imaging.

Impact of different antithrombotics on the microcirculation and viability of perforator-based ischaemic skin flaps in a small animal model

The effects of antithrombotic drugs on random and free flap survival have been investigated in the past, but the experimental and clinical results are not in agreement. A perforator-based critical ischaemia model was used to evaluate the effects of different perioperatively administered pharmaceutical agents on tissue ischaemia and to assess the potential additional haemorheological or vasodilative effects of antithrombotics on flap microcirculation. Combined laser Doppler flowmetry and remission spectroscopy revealed an increase in certain microcirculation parameters in most groups in comparison with saline controls, and these changes correlated with flap survival. Clopidogrel and hirudin significantly improved the amount of viable flap tissue in comparison with controls, while unfractioned heparin had a negative effect on flap survival. Low molecular weight heparin, aspirin, pentoxifylline, and hydroxyethyl starch had no impact on the amount of viable flap tissue. A higher complication rate was observed in all experimental groups, but only clopidogrel had a negative impact on the flap viability. Our results add to the body of evidence supporting the conclusion that perioperative antithrombotic treatment improves flap survival. Clopidogrel and hirudin are effective pharmacological agents that significantly increased the viability of perforator-based skin flaps in rats, but at a higher risk of postoperative bleeding.