Free flap monitoring using simultaneous non-invasive laser Doppler flowmetry and tissue spectrophotometry

Flap Monitoring Techniques: A Review

Postoperative tissue flap vitality monitoring enables early detection of clinical complications, allowing for intervention. Timely re-operation can prevent the need for extensive correction procedures, thus reducing healthcare costs and hospitalization time. Statistics show that monitoring can increase the success rate of flap survival to 95% or higher. However, despite the significant progress in monitoring techniques, major and minor complications, leading to the loss of the flap, still occur. This clinical application review aims to provide a comprehensive overview of the recent advancements and findings in flap surgery reconstructions, transplants, and systems for their postoperative assessment. The literature from the years 1925 to 2024 has been reviewed to capture previous and current solutions for monitoring flap vitality. Clinically acclaimed methods and experimental techniques were classified and reviewed from a technical and clinical standpoint. Physical examination, metabolism change, ultrasound method, and electromagnetic (EM) radiation-based measurement methods were carefully evaluated from the perspective of their considered applications. Guidelines aiding engineers in the future design and development process of monitoring systems were proposed. This paper provides a comprehensive overview of the monitoring techniques used in postoperative flap vitality monitoring. It also gives an overview of each approach and potential ways for future development.

Evaluation of peri-implant perfusion in patients who underwent avascular augmentation or microvascular reconstruction using laser Doppler flowmetry and tissue spectrophotometry: a prospective comparative clinical study

OBJECTIVES

The aim of this study was to evaluate the peri-implant perfusion, such as oxygen saturation, the relative amount of hemoglobin, and blood flow, in implants placed in pristine bone and avascular and microvascular grafts using a non-invasive measurement method.

MATERIALS AND METHODS

A total of 58 patients with 241 implants were included. Among them, 106 implants were based in native bone (group I), 75 implants were inserted into avascular bone grafts (group II), and 60 implants were placed in microvascular bone grafts (group III). Gingival perfusion was measured using laser Doppler flowmetry and tissue spectrophotometry (LDF-TS). Implants with signs of gingival inflammation were excluded to analyze healthy implant perfusion in different bony envelopes.

RESULTS

The mean values for oxygen saturation, relative hemoglobin levels, and blood flow did not differ significantly between the groups (p = 0.404, p = 0.081, and p = 0.291, respectively). There was no significant difference in perfusion between implants that were surrounded by mucosa and implants based within cutaneous transplants (p = 0.456; p = 0.628, and p = 0.091, respectively).

CONCLUSION

No differences in perfusion were found between implants inserted into native bone and implants involving bone or soft tissue augmentation. However, implants based in avascular and microvascular transplants showed higher rates of peri-implant inflammation.

CLINICAL RELEVANCE

Peri-implant perfusion seems to be comparable for all implants after they heal, irrespective of their bony surroundings. Although perfusion does not differ significantly, other factors may make implants in avascular and microvascular transplants vulnerable to peri-implant inflammation.

Does the Anastomosis Recipient Vessel Have an Influence on Free Flap Perfusion in Microvascular Head and Neck Reconstruction-A Retrospective Analysis of 338 Cases with Comparison of Flap Perfusion between Different Arterial and Venous Recipient Vessels in Radial Free Forearm Flaps, Anterolateral Thigh Flaps, and Fibula Free Flaps

Background: Flap perfusion is a prerequisite for microvascular free flap survival and a parameter routinely used for flap monitoring. The aim of this study was to investigate the influence of the anastomosis recipient vessel on flap perfusion. Methods: Flap perfusion was retrospectively analyzed in 338 patients who underwent head and neck reconstruction with microvascular free flaps between 2011 and 2020. The Oxygen-to-see tissue oxygen analysis system measurements for intraoperative and postoperative flap blood flow, hemoglobin concentration, and hemoglobin oxygen saturation at 8 and 2 mm tissue depths were compared between arterial anastomosis recipient vessels (external carotid artery [ECA], facial artery [FAA], lingual artery [LIA], and superior thyroid artery [STA]) and venous anastomosis recipient vessels (internal jugular vein [IJV], combination of IJV and IJV branches, IJV branches, and external jugular vein). Results: The postoperative hemoglobin concentration at 2 mm tissue depth differed significantly between arterial anastomosis recipient vessels (ECA, 41.0 arbitrary units [AU]; FAA, 59.0 AU; LIA, 51.5 AU; STA, 59.0 AU; p = 0.029). This difference did not persist in the multivariable testing (p = 0.342). No other differences in flap blood flow, hemoglobin concentration, or hemoglobin oxygen saturation were observed between the arterial and venous anastomosis recipient vessels (p > 0.05 for all). Conclusions: The arterial and venous recipient vessels used for anastomosis did not influence microvascular free flap perfusion. This underlines the capability of the studied recipient vessels to adequately perfuse free flaps, may explain the observed indifferent flap survival rates between commonly used anastomosis recipient vessels, and implies that the recipient vessel is not a confounding variable for flap monitoring with the Oxygen-to-see tissue oxygen analysis system. Further prospective studies are needed to confirm the findings.

Free Flap Perfusion in Microvascular Head and Neck Reconstruction: Influence of the Number of Ischemia Intervals and Ischemia Duration-A Retrospective Study

BACKGROUND

In microvascular head and neck reconstruction, ischemia of the free flap tissue is inevitable during microsurgical anastomosis and may affect microvascular free flap perfusion, which is a prerequisite for flap viability and a parameter commonly used for flap monitoring. The aim of this study was to investigate the influence of the number of ischemia intervals and ischemia duration on flap perfusion.

METHODS

Intraoperative and postoperative flap blood flow, hemoglobin concentration, and hemoglobin oxygen saturation at 2 and 8 mm tissue depths, as measured with the O2C tissue oxygen analysis system, were retrospectively analyzed for 330 patients who underwent microvascular head and neck reconstruction between 2011 and 2020. Perfusion values were compared between patients without (control patients) and with a second ischemia interval (early or late) and examined with regard to ischemia duration.

RESULTS

Intraoperative and postoperative flap blood flow at 8 mm tissue depth were lower in patients with early second ischemia intervals than in control patients [102.0 arbitrary units (AU) vs 122.0 AU, P = .030; 107.0 AU vs 128.0 AU, P = .023]. Both differences persisted in multivariable analysis. Intraoperative and postoperative flap blood flow at 8 mm tissue depth correlated weakly negatively with ischemia duration in control patients (r = -.145, P = .020; r = -.124, P = .048). Both associations did not persist in multivariable analysis.

CONCLUSIONS

The observed decrease in microvascular flap blood flow after early second ischemia intervals may reflect ischemia-related vascular flap tissue damage and should be considered as a confounding variable in flap perfusion monitoring.

Adjunctive technologies in postoperative free-flap monitoring: a systematic review

Patent microvascular anastomoses are essential for successful free tissue transfer. Early accurate detection of microvascular compromise is required for flap salvage. Adjunctive monitoring techniques, in addition to clinical examination, are increasingly used to detect flap compromise. This systematic review synthesized and appraised the literature to determine the efficacy of different postoperative monitoring technologies. Rates of flap takeback, salvage, failure, and mean time to detection of microvascular compromise were extracted, synthesized, and reviewed. Twenty-two studies were included, comprising 6370 flaps. One thousand three hundred and ninety-five flaps were monitored with Cook Swartz Doppler (21.83%), 1417 flaps with tissue oximetry (22.24%), 291 with laser Doppler (4.56%), 175 with duplex echography (2.74%), 210 with indocyanine green (ICG) fluorescence (3.30%), 196 with Synovis flow coupler (3.07%), and 81 (1.27%) with light spectroscopy. The overall true positive rate for microvascular compromise in taken back flaps was 70.18%. Cook Swartz Doppler (n = 1391) had a true positive rate of 80.17% and 83.63% salvage rate and was associated with an overall 2.60% rate of flap failure. Tissue oximetry (n = 1417) had a true positive rate of 74.76% and a salvage rate of 88.62%. Laser Doppler, duplex echography, light spectroscopy, and Synovis flow coupler demonstrated true positive rates between 69.4% and 100% with salvage rates between 64% and 100%. Cook Swartz Doppler and tissue oximetry are associated with prompt identification of microvascular compromise and return to theatre. Alternative modalities, including near-infrared spectroscopy, laser Doppler, and duplex echography, show promise. Further well-designed randomised controlled trials (RCTs) appraising head-to-head efficacy are required to comparatively assess adjunctive technologies.

Evaluation of perfusion parameters of gingival inflammation using laser Doppler flowmetry and tissue spectrophotometry- a prospective comparative clinical study

BACKGROUND

The aim of this study was to determine the values of different perfusion parameters- such as oxygen saturation, the relative amount of hemoglobin, and blood flow- in healthy subjects compared to patients with gingivitis as a non-invasive measurement method.

METHODS

A total of 114 subjects were enrolled in this study and separated into subjects with gingivitis (50) and without gingivitis (64) based on clinical examination. Gingival perfusion was measured at 22 points in the maxilla and mandible using laser Doppler flowmetry and tissue spectrophotometry (LDF-TS) with the "oxygen to see" device. All patients underwent measurement of gingival perfusion, followed by the clinical evaluation (measurement of probing depths, evaluation of bleeding on probing, plaque level, and biotype). Perfusion parameters were compared between the groups, associations between the non-invasive and clinical measurements were analyzed, and theoretical optimal cut-off values for predicting gingivitis were calculated with receiver operating characteristics.

RESULTS

The mean oxygen saturation, mean relative amount of hemoglobin, and mean blood flow all significantly differed between the groups with and without gingivitis (p = 0.005, p < 0.001, and p < 0.001, respectively). The cut-off value for predicting gingivitis was > 40 AU (p < 0.001; sensitivity 0.90, specificity 0.67).

CONCLUSIONS

As a non-invasive method, LDF-TS can help determine gingival hyperemia. Flow values above 40 AU indicate a higher risk of hyperemia, which can be associated with inflammation. The LDF-TS method can be used for the objective evaluation of perfusion parameters during routine examinations and can signal the progression of hyperperfusion before any change in clinical parameters is observed.

TRIAL REGISTRATION

All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the institutional Clinical Research Ethics Committee (Ethik-Kommission der Medizinischen Fakultät der RWTH Aachen, Decision Number 286/20) and retrospectively registered by the German Clinical Trials Register (File Number DRKS00024048, registered on the 15th of October 2021).

Remote Monitoring System for Condition Management of Patients in Free Flap Surgery

INTRODUCTION

Free flap surgery is inconvenient because an attending physician must observe a patient's condition every day to ensure that normal tissue is restored within 72 h after the surgery. To address this problem, this paper proposes a remote monitoring technology to observe a patient's condition in real time.

METHODS

To design a monitoring system, the camera consists of MCU board, DC-DC converter, alarm performance, Wi-fil module, and server, and the camera and MCU part is connected to the server through the wi-fi network. A camera obtains the images of the surgical site once every 2 s, and the images are transmitted to the attending physician or nurse via Wi-Fi communication. The working distance between camera and surgical site is 56 cm, and the viewing angle of a camera is 60° (radius).

RESULTS

A video shooting test is also performed, in which the images are obtained once per hour between 17:00 and 08:00 the next day; the results show that high-quality images are obtained in the video shooting test. The imaging error is zero (0 GB) in the video shooting test results.

DISCUSSION AND CONCLUSION

The imaging of the surgical site can be obtained by camera system, and the proposed method is that there no storage error occurs during the shooting process. In addition, the shooting performance has high velocity. It is possible to control the WD according to a patient's body via a holding manipulator used for the camera. The new method is expected to be used for remote patient management, for a wide range of procedures, in the medical field.

Attached compared with unattached surface probes for monitoring flap perfusion in microvascular head and neck reconstruction: a feasibility study

Unattached surface probes are commonly used with the O2C analysis system (LEA Medizintechnik, Germany) to monitor microvascular free flap perfusion. This study compared attached and unattached surface probes for extraoral free flaps. The study included 34 patients who underwent extraoral microvascular head and neck reconstruction between 2020 and 2022. Flap perfusion was monitored postoperatively using the O2C analysis system at 0, 12, 24, 36, and 48 h, with an attached surface probe at 3 mm tissue depth and an unattached surface probe at 2 mm and 8 mm tissue depths. Clinical complications, technical errors, and perfusion measurement values were compared. No clinical complications (attachment suture infections) or technical errors (probe detachment) occurred. Flap blood flow values of the probes were partially different (3 mm vs. 2 and 8 mm: p < 0.001; p = 0.308) and moderately correlated (3 mm with 2 and 8 mm: r = 0.670, p < 0.001; r = 0.638, p < 0.001). Hemoglobin concentration and oxygen saturation values were generally different (3 mm vs. 2 and 8 mm: all p < 0.001) and variably correlated (3 mm with 2 and 8 mm: r = 0.756, r = 0.645; r = 0.633, r = 0.307; all p < 0.001). Both probes are comparable in terms of technical feasibility and patient safety, with flap perfusion values dependent on tissue measurement depth.

Flap perfusion monitoring with an attached surface probe in microvascular reconstruction of the oral cavity

OBJECTIVES

Postoperative flap monitoring is essential in oral microvascular reconstruction for timely detection of vascular compromise. This study investigated the use of attached surface probes for the oxygen-2-see (O2C) analysis system (LEA Medizintechnik, Germany) for intraoral flap perfusion monitoring.

MATERIALS AND METHODS

The study included 30 patients who underwent oral reconstruction with a microvascular radial-free forearm flap (RFFF) or anterolateral thigh flap (ALTF) between 2020 and 2022. Flap perfusion was measured with attached (3-mm measurement depth) and unattached surface probes (2- and 8-mm measurement depths) for the O2C analysis system at 0, 12, 24, 36, and 48 h postoperatively. Flap perfusion monitoring with attached surface probes was evaluated for cut-off values for flap blood flow, hemoglobin concentration, and hemoglobin oxygen saturation indicative of vascular compromise and for accuracy and concordance with unattached surface probes.

RESULTS

Three RFFFs were successfully revised, and one ALTF was unsuccessfully revised. The cut-off values indicative of vascular compromise for flap perfusion monitoring with attached surface probes were for RFFF and ALTF: blood flow < 60 arbitrary units (AU) and < 40AU, hemoglobin concentration > 100AU and > 80AU (both > 10% increase), and hemoglobin oxygen saturation < 40% and < 30%. Flap perfusion monitoring with attached surface probes yielded a 97.1% accuracy and a Cohen's kappa of 0.653 (p < 0.001).

CONCLUSIONS

Flap perfusion monitoring with attached surface probes for the O2C analysis system detected vascular compromise accurately and concordantly with unattached surface probes.

CLINICAL RELEVANCE

Attached surface probes for the O2C analysis system are a feasible option for intraoral flap perfusion monitoring.

An early microvascular training program of dental intern students and junior residents: a comparative prospective study

BACKGROUND

Clinical instructional strategies and the climate in which teaching and learning take place have a significant impact on the quality of dental education. Therefore, this study aimed to evaluate the impact of early microsurgery training on the skills of dental intern students who are planning to join an oral and maxillofacial surgical field (DIS) as compared with junior residents within an oral and maxillofacial surgery department who had no microsurgery experience (JR).

METHODS

A total of 100 trainees, 70 were DIS, while the other 30 were JR. The average age was 23.87 ± 2.05 years for DIS group and 31.05 ± 3.06 for JR group. All trainees attended a microsurgical course (theoretical and practical parts) for seven days within a Microvascular Laboratory for Research and Education of a university-affiliated tertiary hospital. Two blinded examiners had assessed the performance of trainees independently using a specific scoring system. The independent sample t-test was used to compare the effect of microsurgery training between DIS and JR groups. The significance level was set at 0.05.

RESULTS

The DIS group had showed higher attendance rate than JR group (p < 0.01), with a lower absence score in DIS than JR groups (0.33 ± 0.58 vs. 2.47 ± 1.36). The total score of the theoretical test was significantly different between both groups (p < 0.01). In this context, the DIS group had revealed higher total score than JR group (15.06 ± 1.92 vs. 12.73 ± 2.49). In term of tissue preservation, there was a significant difference between both groups, with the DIS had better performance score than JR (1.49 ± 0.51 vs. 0.93 ± 0.59). Further, the practical exam score was significantly higher in DIS group than JR group (p < 0.01).

CONCLUSION

Overall, the performance of dental intern students was favourably compared with junior residents in most aspects. Therefore, it is promising and essential for dental colleges to add a microsurgery course to the curriculum of dental intern students who plan to specialize in oral and maxillofacial surgery.

On-skin biosensors for noninvasive monitoring of postoperative free flaps and replanted digits

Severe soft tissue defects and amputated digits are clinically common injuries. Primary treatments include surgical free flap transfer and digit replantation, but these can fail because of vascular compromise. Postoperative monitoring is therefore crucial for timely detection of vessel obstruction and survival of replanted digits and free flaps. However, current postoperative clinical monitoring methods are labor intensive and highly dependent on the experience of nurses and surgeons. Here, we developed on-skin biosensors for noninvasive and wireless postoperative monitoring based on pulse oximetry. The on-skin biosensor was made of polydimethylsiloxane with gradient cross-linking to create a self-adhesive and mechanically robust substrate that interfaces with skin. The substrate was shown to exhibit appropriate adhesion on one side for both high-fidelity measurements of the sensor and low risk of peeling injury to delicate tissues. The other side demonstrated mechanical integrity to facilitate flexible hybrid integration of the sensor. Validation studies using a model of vascular obstruction in rats demonstrated the effectiveness of the sensor in vivo. Clinical studies indicated that the on-skin biosensor was accurate and more responsive than current clinical monitoring methods in identifying microvascular conditions. Comparisons with existing monitoring techniques, including laser Doppler flowmetry and micro-lightguide spectrophotometry, further verified the sensor's accuracy and ability to identify both arterial and venous insufficiency. These findings suggest that this on-skin biosensor may improve postoperative outcomes in free flap and replanted digit surgeries by providing sensitive and unbiased data directly from the surgical site that can be remotely monitored.

Impacts of vascular comorbidities on free flap perfusion in microvascular head and neck reconstruction

PURPOSE

Arterial hypertension (AHTN), type 2 diabetes mellitus (DM), and atherosclerotic vascular disease (ASVD) are common vascular comorbidities in patients undergoing reconstruction of the head and neck region with a microvascular free flap. These conditions may affect flap perfusion (microvascular blood flow and tissue oxygenation), which is a prerequisite for flap survival and thus reconstruction success. This study aimed to investigate the impacts of AHTN, DM, and ASVD on flap perfusion.

METHODS

Data from 308 patients who underwent successful reconstruction of the head and neck region with radial free forearm flaps, anterolateral thigh flaps, or fibula free flaps between 2011 and 2020 were retrospectively analyzed. Flap perfusion was measured intraoperatively and postoperatively with the O2C tissue oxygen analysis system. Flap blood flow, hemoglobin concentration, and hemoglobin oxygen saturation were compared between patients with and without AHTN, DM, and ASVD.

RESULTS

Intraoperative hemoglobin oxygen saturation and postoperative blood flow were lower in patients with ASVD than in patients without ASVD (63.3% vs. 69.5%, p = 0.046; 67.5 arbitrary units [AU] vs. 85.0 AU, p = 0.036; respectively). These differences did not persist in the multivariable analysis (all p > 0.05). No difference was found in intraoperative or postoperative blood flow or hemoglobin oxygen saturation between patients with and without AHTN or DM (all p > 0.05).

CONCLUSION

Perfusion of microvascular free flaps used for head and neck reconstruction is not impaired in patients with AHTN, DM, or ASVD. Unrestricted flap perfusion may contribute to the observed successful use of microvascular free flaps in patients with these comorbidities.

One-Pot Synthesis of Bioadhesive Double-Network Hydrogel Patch as Disposable Wound Dressing

Inventions of materials to achieve biocompatibility, bioadhesion, and easy manufacturing are the urgent demand for promoting wound healing in clinical treatment. Hyaluronic acid (HA) is probably the ideal candidate for current dressing materials due to its well-known biocompatibility. However, the unavoidable problem for HA dressings is their inherent low adhesiveness to wounds, which severely impairs their treatment efficacy, especially during body movement. Here, we report a one-pot facile fabrication of hybrid double-network polydopamine-HA (PDA-HA) hydrogel with significantly enhanced adhesiveness compared to the HA hydrogel. Besides the easy manufacturing and promoted effectiveness, the PDA-HA hydrogel could be vacuum-dried to form a patch, further benefitting from the convenience for storage and distribution. When applied on the wound, the PDA-HA patch quickly rehydrated by absorbing exudate and stuck tightly to the wound. The applied PDA-HA patches keep the wounds covered for more than 7 days against strenuous exercise. Thus, mouse full-thickness wounds treated with the PDA-HA patches exhibited increased healing rates, where epithelization was finished within 14 days. Moreover, the hydrogel dressing exhibited promoting effects on vascularization and cell proliferation/migration. Together with the easy manufacturing procedure, good adhesion/adaptation, and promotion of wound healing, the PDA-HA patch holds great potential for future clinical translation.

Blood flow analyses by intraoperative transit-time flow measurements of free flaps for head and neck reconstructions: A prospective single-center study

BACKGROUND

The behavior of blood flow changes within free flaps following microvascular anastomosis is not well described in the literature. The aim of this study was to determine the immediate blood flow behavior of different free flaps as reference values for various clinical applications.

METHODS

Intraoperative transit-time flow measurements were performed on patients receiving free flap transfer in the head and neck area comprising radial forearm flaps (RFF), peroneal artery perforator flaps (PAP), anterolateral thigh flaps (ALT), vastus lateralis flaps (VLF), parascapular flaps (PSF), latissimus dorsi flaps (LDF), fibula free flaps (FFF), deep circumflex iliac artery flaps (DCIA), and scapular flaps (SF). In accordance with a structured protocol, measurements took place at the pedicle directly before flap harvesting and at the recipient vessels 1 h after flap transfer. Heart rate, transplant weight, and other patient characteristics were recorded and analyzed.

RESULTS

A total of 129 were enrolled, comprising 66 RFF, 8 ALT, 6 PAP, 11 VLF, 3 PSF, 2 LDF, 24 FFF, 7 DCIA, and 2 SF. In most of the transplant groups, arterial perfusion increased after anastomosis at the recipient site. The arterial pulsatility index developed indirectly proportionally to arterial blood flow, whereas venous blood drainage did not show any statistically significant changes. Muscle flaps had the highest arterial perfusion before flap transfer. Composite transplants with hard and soft tissue presented the greatest increase in arterial perfusion. The lowest arterial blood flow after anastomosis was measured in PAP and RFF. In contrast, RFF and PAP presented the highest arterial perfusion per 100 g transplant weight.

CONCLUSIONS

Arterial perfusion changed, whereas venous blood flow did not show any statistically significant variations in any transplant group. Perfusion of free flaps does not only depend on the recipient vessel and the recipient bed, but also on flap-specific anatomy and physiology.

Postoperative free flap monitoring in reconstructive surgery-man or machine?

Free tissue transfer is widely used for the reconstruction of complex tissue defects. The survival of free flaps depends on the patency and integrity of the microvascular anastomosis. Accordingly, the early detection of vascular comprise and prompt intervention are indispensable to increase flap survival rates. Such monitoring strategies are commonly integrated into the perioperative algorithm, with clinical examination still being considered the gold standard for routine free flap monitoring. Despite its widespread acceptance as state of the art, the clinical examination also has its pitfalls, such as the limited applicability in buried flaps and the risk of poor interrater agreement due to inconsistent flap (failure) appearances. To compensate for these shortcomings, a plethora of alternative monitoring tools have been proposed in recent years, each of them with inherent strengths and limitations. Given the ongoing demographic change, the number of older patients requiring free flap reconstruction, e.g., after cancer resection, is rising. Yet, age-related morphologic changes may complicate the free flap evaluation in elderly patients and delay the prompt detection of clinical signs of flap compromise. In this review, we provide an overview of currently available and employed methods for free flap monitoring, with a special focus on elderly patients and how senescence may impact standard free flap monitoring strategies.

How do i salvage that flap?; An evidence-based primer on salvage techniques for head & neck microvascular free flaps

Interventional strategies for dealing with microvascular free flap failure are varied among institutions and even individual surgeons. This systematic review aims to identify the published methods for salvaging a failing free flap and provide surgeons with a comprehensive toolset for successful intervention. A title and abstract search of the PubMed, Embase, and Web of Science databases was performed. 1694 abstracts were screened by three reviewers according to Prisma guidelines. 62 full text articles meeting inclusion criteria detailed techniques which were separated into the categories of thrombectomy, thrombolysis, leech therapy, vascular fistula, and an "other" category outlining techniques which did not fit into the prior framework. Assessment of the efficacy of individual salvage techniques is limited due to limited empirical data, however, the approach to successful salvage should be based on timely identification of flap compromise, followed by the implementation of one or several of the aforementioned techniques.

Harnessing the Power of Artificial Intelligence: Revolutionizing Free Flaps Monitoring in Head and Neck Tumor Treatment

Treating head and neck tumors has undergone significant advancements, focusing on improving the patient's quality of life after treatment. Reconstructive surgical techniques with free flaps have been vital in restoring anatomy, function, and aesthetics, reducing morbidity from locoregional treatments. Monitoring free flaps is crucial to detect and address any vascular compromise that may lead to flap failure. Various monitoring techniques have been employed in free flap monitoring. However, standardizing them presents a challenge due to the need for more consensus among surgeons and variability in techniques, costs, and training requirements. Artificial intelligence (AI) shows promise in standardizing monitoring practices and reducing the operator-dependent variability. AI techniques have been explored to improve monitoring and early detection of complications in free flap surgeries, and they have shown high accuracy in analyzing images and predicting flap outcomes. Despite the potential benefits, implementing AI in free flap monitoring remains challenging. Standardization of input data, interpretation, cost, training, and accounting for patient and flap variability are crucial considerations. Further research, including multicenter studies, validation, and collaboration amongst clinicians, researchers, and AI experts is needed to overcome these challenges.

Perfusion of microvascular free flaps in head and neck reconstruction after prior neck dissection and irradiation

Microvascular free flaps are frequently used for head and neck reconstruction after prior neck dissection (ND) and neck irradiation (RTX). The aim of this study was to investigate the influence of ND and RTX on flap perfusion as a critical factor for flap success. Overall, 392 patients reconstructed with a microvascular fasciocutaneous flap (FF) or perforator flap (PF) in the head and neck region between 2011 and 2020 were analysed retrospectively. Flap perfusion measured intraoperatively and postoperatively with the O2C tissue oxygen analysis system was compared between patients who had received neither ND nor RTX (controls), patients who had received ND but no RTX (ND group), and patients who had received both ND and RTX (ND+RTX group). Intraoperative and postoperative flap blood flow was decreased in FFs in ND group patients compared to controls (median 66.3 AU vs 86.0 AU, P = 0.023; median 73.5 AU vs 93.8 AU, P = 0.045, respectively). In the multivariable analysis, these differences showed a tendency to persist (P = 0.052 and P = 0.056). Flap success rates were similar in control patients, ND patients, and ND+RTX patients (98.7%, 94.0%, and 97.6%, respectively). Flap perfusion is not reduced in FFs and PFs in patients who have undergone ND or ND and RTX. This indicates that neck dissection and neck irradiation should not be contraindications for microvascular free flap reconstruction.

Hyperspectral Imaging Allows Evaluation of Free Flaps in Craniomaxillofacial Reconstruction

INTRODUCTION

Treatment of extended defects after tumor resection in oral, maxillofacial, and facial surgery (craniomaxillofacial) is usually performed by free microvascular flaps. Evaluation of flap survival is crucial, especially in the first hours after insertion and connection. For flap evaluation various invasive and noninvasive methods have been developed. This retrospective clinical study examined the ability of a hyperspectral imaging (HSI) camera (Tivita, Diaspective Vision, Germany) to assess postoperative flap properties in comparison to established clinical parameters.

MATERIALS AND METHODS

Thirteen patients with tumor resection and free flap reconstruction were included for camera analysis and another 10 patients as control group. For this purpose, at defined time intervals and under standardized conditions, recordings of transplants 3 to 100 hours postoperatively were performed. Images were used to examine oxygenation (StO2%), tissue hemoglobin index, tissue water index, near infrared range perfusion index of free flaps quantitatively and qualitatively.

RESULTS

HSI provides values differing between patients observed with no intraindividual significant difference. After 24 hours a mean reduction of 16.77% for StO2%, 9.16% for tissue hemoglobin index and 8.46% was observed, going in line with no loss of flap was noted in the observation period.

CONCLUSION

HSI is suitable as a noninvasive measure for the evaluation of free flaps in craniomaxillofacial surgery in case of stable imaging conditions with respect to light, surrounding and position of the camera. However, clinical measurements are still the method of choice.

Smoking and microvascular free flap perfusion in head and neck reconstruction: radial free forearm flaps and anterolateral thigh flaps

Head and neck reconstruction with microvascular free flaps is frequently performed in smokers. Smoking causes various alterations in the cardiovascular system. The aim of this study was to investigate the effects of smoking on flap perfusion as a critical factor for flap survival. A total of 370 patients reconstructed with a radial free forearm flap (RFFF) or anterolateral thigh flap (ALTF) in the head and neck region between 2011 and 2020 were retrospectively analyzed. Flap perfusion measurements with the O2C tissue oxygen analysis system were compared between nonsmokers, light smokers (< 20 pack-years), and heavy smokers (≥ 20 pack-years). The blood flow was intraoperatively equal in RFFFs (84.5 AU vs. 84.5 AU; p = 0.900) and increased in ALTFs (80.5 AU vs. 56.5 AU; p = 0.001) and postoperatively increased in RFFFs (114.0 AU vs. 86.0 AU; p = 0.035) and similar in ALTFs (70.5 AU vs. 71.0 AU; p = 0.856) in heavy smokers compared to nonsmokers. The flap survival rate was similar in nonsmokers, light smokers, and heavy smokers (97.3%, 98.4%, and 100.0%). Smoking partially increases rather than decreases microvascular free flap perfusion, which may contribute to similar flap survival rates in smokers and nonsmokers.

Comparing the Time-Dependent Evolution of Microcirculation in Gracilis vs. ALT Flaps Using Laser-Doppler Flowmetry and Tissue-Spectrometry

Postoperative free flap monitoring is considered a key component of care after microsurgical reconstruction. To achieve successful flap salvage after surgical revision, early recognition of vascular compromise is required. The aim of this study was to assess and compare the time-dependent evolution of microcirculation in gracilis muscle (GM) and anterolateral thigh (ALT) flaps. This study included continuous measurements of blood flow (flow), hemoglobin oxygenation (SO2) and the relative amount of hemoglobin (rHb) using laser-doppler flowmetry and tissue-spectrometry (O2C, LEA Medizintechnik, Gießen, Germany) over a time-period of 72 h. Microcirculation was assessed in a total of 66 viable free flaps (GM n = 40; ALT n = 26). A statistically significant positive correlation between time post-anastomosis and microvascular flow was found for both GM and ALT flaps with rs = 0.384 (p < 0.001) and rs = 0.178 (p = 0.015), respectively. No significant positive or negative correlations between time post-anastomosis and SO2 were found for both GM and ALT flaps with rs = 0.052 (p = 0.387) and rs = −0.018 (p = 0.805), respectively. Overall, a significant negative correlation between time post-anastomosis and rHb was found for GM flaps with rs = −0.140 (p = 0.019). For ALT flaps, no significant positive or negative correlation was found with rs = −0.011 (p = 0.887). Microcirculation differs in different flap entities, and surgeons should be aware of these differences in order to correctly evaluate and classify the values of flow, SO2 and rHb obtained when using the O2C device for postoperative monitoring.

The 72-Hour Microcirculation Dynamics in Viable Free Flap Reconstructions

BACKGROUND

 The risk for vascular complications is the highest within the first 24 hours after free flap transfer. Clinical signs of critical perfusion are often recognized with time delay, impeding flap salvage. To detect failing flaps as soon as possible and to prevent persisting microvascular impairments, knowledge of physiological perfusion dynamics in free flaps is needed. Aim of this study was to investigate the physiological perfusion dynamics of viable free flaps using the Oxygen to See (O2C) device for continuous monitoring.

METHODS

 Microcirculation was continuously monitored in 85 viable free flaps over a period of up to 72 hours following microvascular anastomosis using tissue spectrophotometry and laser Doppler flowmetry (O2C, LEA Medizintechnik, Gießen, Germany). The parameters investigated included capillary-venous blood flow (flow), oxygen saturation (SO₂), and relative amount of hemoglobin (rHB).

RESULTS

 Microcirculatory blood flow increased significantly overall, especially within the first 18 hours after microsurgical anastomosis, after which peak formation was occurred. Mean values of SO₂ showed a decreasing trend and the steepest decrease of SO₂ (slope: 1.0) occurred during the steepest increase of flow between 3 and 6 hours (slope: 4.7) postanastomosis. The rHB values remained fairly constant throughout the study period.

CONCLUSION

 Hyperemia after free flap transfer accounts for a significant increase of microvascular flow. Tissue oxygenation is reduced, likely due to an increase of oxygen consumption after anastomosis. A better understanding of physiological perfusion dynamics in free flaps can aid surgeons in recognizing compromised vasculature earlier and improve free flap salvage.

Flap Monitoring Using Transcutaneous Oxygen or Carbon Dioxide Measurements

Free tissue transfer is a cornerstone of complex reconstruction. In many cases, it represents the last option available for a patient and their reconstruction. At high-volume centers, the risk of free flap failure is low but its occurrence can be devastating. Currently, the mainstay for flap monitoring is the clinical examination. Though reliable when performed by experienced clinicians, the flap exam is largely subjective, is performed discontinuously, and often results in significant time delay between detection of flap compromise and intervention. Among emerging flap monitoring technologies, the most promising appear to be those that rely on noninvasive transcutaneous oxygen and carbon dioxide measurements, which provide information regarding flap perfusion. In this article, we review and summarize the literature on various techniques but primarily emphasizing those technologies that rely on transcutaneous gas measurements. We also define characteristics for the ideal flap monitoring tool and discuss critical barriers, predominantly cost, preventing more widespread utilization of adjunct monitoring technologies, and their implications.

New Approach to the Old Challenge of Free Flap Monitoring-Hyperspectral Imaging Outperforms Clinical Assessment by Earlier Detection of Perfusion Failure

In reconstructive surgery, free flap failure, especially in complex osteocutaneous reconstructions, represents a significant clinical burden. Therefore, the aim of the presented study was to assess hyperspectral imaging (HSI) for monitoring of free flaps compared to clinical monitoring. In a prospective, non-randomized clinical study, patients with free flap reconstruction of the oro-maxillofacial-complex were included. Monitoring was assessed clinically and by using hyperspectral imaging (TIVITA™ Tissue-System, DiaspectiveVision GmbH, Pepelow, Germany) to determine tissue-oxygen-saturation [StO₂], near-infrared-perfusion-index [NPI], distribution of haemoglobin [THI] and water [TWI], and variance to an adjacent reference area (Δreference). A total of 54 primary and 11 secondary reconstructions were performed including fasciocutaneous and osteocutaneous flaps. Re-exploration was performed in 19 cases. A total of seven complete flap failures occurred, resulting in a 63% salvage rate. Mean time from flap inset to decision making for re-exploration based on clinical assessment was 23.1 ± 21.9 vs. 18.2 ± 19.4 h by the appearance of hyperspectral criteria indicating impaired perfusion (StO₂ ≤ 32% OR StO₂Δreference > −38% OR NPI ≤ 32.9 OR NPIΔreference ≥ −13.4%) resulting in a difference of 4.8 ± 5 h (p < 0.001). HSI seems able to detect perfusion compromise significantly earlier than clinical monitoring. These findings provide an interpretation aid for clinicians to simplify postoperative flap monitoring.

Intraluminal Monitoring of Micro Vessels. A Surgical Feasibility Study

Objective: Monitoring of vessel perfusion is of high clinical importance in vascular anastomosis of free flaps. Current sensor systems are based on different principles and show limitations in validity and accuracy. Fiber optic pressure sensors exhibit high accuracy and are small in size. The aim of the present study was to evaluate the surgical feasibility of intraluminal pressure (ILP) measurements with a fiber optic pressure sensor in an animal model. Methods: In a microsurgical setting we sedated 10 Wistar rats with weight adapted phenobarbital, xylazine, and fentanyl. We performed a surgical approach to A. carotis communis and V. jugularis and introduced a 600 μm fiber optic pressure sensor into the vessels followed by measuring the ILP. The sensor was stabilized by the surrounding tissue, and the vessels were closed. Results: In all cases, surgical placement was uneventful. Measurement of intra-venous and intra-arterial pressure was possible and stable over the whole measurement period of an hour. Conclusion: Fiber optic pressure measurement in microvessels is possible and surgically feasible. An application to monitor the perfusion of free flaps seems possible.

Intraoperative Indocyanine Green Angiography for Assessing Flap Perfusion in Skull Base Reconstruction: A Systematic Review

Objective This study was aimed to study the current use of intraoperative indocyanine green (ICG) angiography during skull base reconstruction and understand its efficacy in predicting postoperative magnetic resonance imaging (MRI) enhancement and flap.

Study Design The Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, and Google Scholar databases were searched from the date of inception until August 2020 for studies of ICG flap perfusion assessment during skull base reconstruction. The primary outcome of interest was the development of cerebrospinal fluid (CSF) leak after skull base reconstruction. Secondary outcomes of interest included postoperative meningitis, flap MRI enhancement, flap necrosis, flap perfusion measurements, and total complications.

Results Search results yielded 189 studies, from which seven studies with a total of 104 patients were included in the final analysis. There were 44 nasoseptal flaps (NSF), two lateral nasal wall flaps (LNWF), 14 pericranial flaps (PCF), and 44 microvascular free flaps. The rates of CSF leak and postoperative MRI enhancement were 11 and 94%, respectively. There was one case of postoperative meningitis. Pooled analysis of the available data showed that intraoperative ICG flap perfusion was associated with flap enhancement on postoperative MRI (p = 0.008) and CSF leak (p = 0.315) by Fisher's exact test.

Conclusion The available literature suggests intraoperative ICG enhancement is associated with postoperative MRI enhancement. Given the small sample sizes in the literature and the rarity of complications associated with skull base reconstruction, intraoperative ICG enhancement has not been predictive of flap necrosis or postoperative complications such as CSF leak or meningitis.

Level of Evidence This study presents level 3 evidence as a systematic review of case studies, case reports, and retrospective and prospective trials with no blinding, controls, and inconsistently applied reference standards.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part I: Summary and brief description of monitoring methods

Micro-vascular flaps have been used for the repair of challenging defects for over 45 years. The risk of failure is reported to be around 5-10% which despite medical and technical advances in recent years remains essentially unchanged. Precise, continuous, sensitive and specific monitoring together with prompt notification of vascular compromise is crucial for the success of the procedure. In this review, we provide a classification and brief description of the reported methods for monitoring the micro-vascular flap and a summary of the benefits over direct visual monitoring. Over 40 different monitoring techniques have been reported but their comparative merits are not always obvious. One looks for early detection of a flap's compromise, improved flap salvage rate and a minimal false-positive or false-negative rate. The cost-effectiveness of any method should also be considered. Direct visualisation of the flap is the method most generally used and still seems to be the simplest, cheapest and most reliable method for flap monitoring. Considering the alternatives, only implantable Doppler ultrasound probes, near infrared spectroscopy and laser Doppler flowmetry have shown any evidence of improved flap salvage rates over direct visual monitoring.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part II: Clinical application

Despite the high success rate of micro-vascular flaps, anastomosis compromise occurs in 5-10% and that can lead to flap failure. Reliable monitoring of the flap is therefore of similar importance to that of the precise surgical procedure itself. Multiple methods have been reported for monitoring of the flap vitality, the first one being direct visual monitoring. In buried flaps direct visualisation is not feasible or is unreliable. In these cases we can extend the buried flap to expose a segment of it to act as a monitoring sentinel. For the purpose of this review we used our clinical experience as a starting point, and for the extended information and expertise we conducted a search of the PubMed database. Over 40 monitoring techniques have been reported to-date. Direct visual monitoring is still generally used method with a reliability of up to 100% and an overall success rate of up to 99%. Direct visualisation remains as the simplest, cheapest and yet a very reliable method of flap monitoring. In this review we provide a description of various possible techniques for externalising part of a buried flap, define the tissues that can be used for this purpose and we summarise the procedures that should be followed to achieve the best reliability and validity of monitoring the skin island.

Hyperspectral analysis for perioperative perfusion monitoring-a clinical feasibility study on free and pedicled flaps

OBJECTIVES

In reconstructive surgery, flap monitoring is crucial for early identification of perfusion problems. Using hyperspectral imaging (HSI), this clinical study aimed to develop a non-invasive, objective approach for perfusion monitoring of free and pedicled flaps.

MATERIAL AND METHODS

HSI of 22 free (FF) and 8 pedicled flaps (PF) in 30 patients was recorded over time. Parameters assessed were tissue oxygenation/superficial perfusion (0-1 mm) (StO2 (0-100%)), near-infrared perfusion/deep perfusion (0-4 mm) (NIR (0-100)), distribution of haemoglobin (THI (0-100)), and water (TWI (0-100)). Measurements up to 72 h were correlated to clinical assessment.

RESULTS

Directly after flap inset, mean StO2 was significantly higher in FF (70.3 ± 13.6%) compared with PF 56.2 ± 14.2% (p = 0.05), whereas NIR, THI, and TWI were similar (NIR_p = 0.82, THI_p = 0.97, TWI_p = 0.27). After 24 h, StO2, NIR, THI, and TWI did not differ between FF and PF. After 48 h, StO2, NIR, and TWI did not differ between FF and PF whereas THI was significantly increased in FF compared with PF(p = 0.001). In three FF, perfusion decreased clinically and in HSI, 36(1), 40(2), 5(3), and 61(3) h after flap inset which was followed by prompt intervention.

CONCLUSIONS

StO2 < 40%, NIR < 25/100, and THI < 40/100 indicated arterial occlusion, whereas venous problems revealed an increase of THI. In comparison with FF, perfusion parameters of PF were decreased after flap transfer but remained similar to FF later on.

CLINICAL RELEVANCE

HSI provides objective and non-invasive perfusion monitoring after flap transplantation in accordance to the clinical situation. With HSI, signs of deterioration can be detected hours before clinical diagnosis.

WALANT-Epinephrine injection may lead to short term, reversible episodes of critical oxygen saturation in the fingertips

INTRODUCTION

Although the WALANT technique's long-term safeness has been demonstrated in many studies, there are only few data investigating its short-term effects on tissue perfusion and oxygen levels. It was hypothesized that, temporarily, critical levels of tissue perfusion may occur.

METHODS

Seventeen patients, who were scheduled for different procedures in WALANT technique, were injected with 5-7 ml of 1% Articain containing 1:200,000 epinephrine at the finger base. Capillary-venous oxygen saturation, hemoglobin volume in the capillaries, and relative blood flow in the fingertips were recorded once per second by white light spectrometry and laser Doppler flowmetry before, during and after injection for an average of 32 min.

RESULTS

Clinically, no persistent tissue malperfusion was observed, and there were no postoperative complications. Capillary-venous oxygen saturation was reduced by ≥ 30% in seven patients. Critical levels of oxygen saturation were detected in four patients during 13 intervals, each lasting for 132.5 s on average. Oxygen saturation returned to noncritical values in all patients by the end of the observation period. Blood flow in the fingertips was reduced by more than 30% in nine patients, but no critical levels were observed, as with the hemoglobin. Three patients demonstrated a reactive increase in blood flow of more than 30% after injection.

CONCLUSIONS

Injection of tumescent local anesthesia containing epinephrine into finger base may temporarily cause a substantial reduction in blood flow and lead to critical levels of oxygen saturation in the fingertips. However, this was fully reversible within minutes and does not cause long-term complications.

The Use of Indocyanine Green Angiography for Cosmetic and Reconstructive Assessment in the Head and Neck

Reconstructive procedures in the head and neck can be a surgical challenge owing to the complex anatomical and physiological structure. Different locoregional and microvascular flaps are used for various defects to improve both function and cosmesis. Subjective clinical findings have been the mainstay for perfusion monitoring; however, areas of borderline perfusion are much more difficult to assess clinically. Multiple technologies that offer objective perfusion assessment have been developed to improve surgical outcomes. Indocyanine green (ICG) angiography has gained popularity owing to its minimal invasiveness and increased sensitivity and specificity in assessing flap perfusion particularly in the head and neck. It has been extensively used in free flaps, pedicled flaps (including nasal reconstruction), facelift procedures, random flaps, skull base reconstruction, and pharyngocutaneous fistula prediction. Its perioperative use has provided valuable qualitative and quantitative data that aid our understanding of flap hemodynamics. Clinically, this impacted decision-making in flap design, harvest, inset, and precocious salvage interventions. Though increased cost and intraoperative time could be limitations, cost-effectiveness studies have supported its use, particularly in high-risk individuals. Limitations include the lack of standardized dosing and consistent methodology agreement for data analysis. Future studies should involve larger cohorts and multi-institute studies to overcome such limitations.

Review of Flap Monitoring Technology in 2020

Advances in free flap reconstruction of complex head and neck defects have allowed for improved outcomes in the management of head and neck cancer. Technical refinements have decreased flap loss rate to less than 4%. However, the potential for flap failure exists at multiple levels, ranging from flap harvest and inset to pedicle lay and postoperative patient and positioning factors. While conventional methods of free flap monitoring (reliant on physical examination) remain the most frequently used, additional adjunctive methods have been developed. Herein we describe the various modalities of both invasive and noninvasive free flap monitoring available to date. Still, further prospective studies are needed to compare the various invasive and noninvasive technologies and to propel innovations to support the early recognition of vascular compromise with the goal of even greater rates of flap salvage.

Comparison Between the Impact of Vasopressors and Goal-Directed Fluid Therapy on the Management of Free Flap Reconstruction of Head and Neck and Monitoring in ICU

Head and neck reconstructions are often accompanied with complex long surgical procedures. Free flap tissue transfer is a standard reconstruction method that reestablishes severe tissue defects after resection due to trauma or cancer. Imbalanced fluid resuscitation can extremely harm the outcome of the flap either due to hypoperfusion or edema. Flap-related postoperative complications mainly flap failure necessitates the administration of a large amount of intravenous fluids perioperatively especially with lengthy operative time. Therefore, vasopressors may be used to preserve hemodynamic stability without excessive fluids use. Nevertheless, these vasopressors have long been disfavored as they may provoke anastomosis vasoconstriction leading to graft hypoperfusion and finally flap failure. However, according to recent guidelines, they are now well-thought to be safe. Of note, inotropes have been confirmed to increase blood flow in the anastomosis hence they can replace vasoconstrictors. Recently, goal-directed fluid therapy (GDFT) has been proven to be excellent in high-risk head and neck free tissue transfer surgery as it decreases prolonged intensive care unit (ICU) admission hospitalization and complication rate. Today, GDFT is highly suggested as one of the enhanced recoveries after surgery protocols for major head and neck free flap reconstruction surgery.

Nursing Monitoring of Microsurgical Free Flaps: Identifying and Addressing Knowledge Gaps

BACKGROUND

 Microsurgical free flaps require careful monitoring to detect early signs of compromise. At many hospitals, nursing staff provides the majority of postoperative monitoring of free flap patients and it lies within their responsibility to alert physicians of a failing free flap. The aim of this study is to identify knowledge gaps in the monitoring of microvascular free tissue transfer in both novice and experienced nurses and to provide appropriate education to address these gaps.

METHODS

 This was a pre- and postintervention study. An initial pilot survey was administered to identify knowledge deficiencies. A nursing educational session on free flap physiology and monitoring was then designed to address these deficiencies. An 18-question multiple choice quiz was administered before and after the educational session. Pre- and post-test scores were compared based on nursing experience. At 6 months, the participating nurses completed a survey rating their confidence with free flap patient care as a result of the educational session.

RESULTS

 A total of 72 nurses completed the in-service training course and quiz. The average quiz score increased from 61.9 to 89.3% after the in-service (p < 0.001). There was no correlation between precurriculum test scores and nursing experience as referenced by total number of years in the profession (r _s = -0.038, p = 0.754). The follow-up survey showed that prior to the course 38% of respondents reported little or no confidence caring for free flap patients, decreasing to 6% after the course (p < 0.05).

CONCLUSION

 Based on the results of this study, nursing knowledge of capillary refill, venous congestion, and basic microsurgical free flap physiology is inadequate. With implementation of a teaching in-service curriculum highlighting these key areas of deficiencies, nurses improved both their understanding and confidence levels, regardless of their level of experience.

Neovascularization Perfusion of Melolabial Flaps Using Intraoperative Indocyanine Green Angiography

Importance

Assessment of melolabial flap perfusion using indocyanine green (ICG) angiography for nasal reconstruction has not been previously described.

Objective

To assess melolabial flap relative perfusion using ICG angiography in nasal reconstruction and highlight its clinical relevance.

Design, Setting, and Participants

In this retrospective case series at a tertiary referral center, 10 patients undergoing melolabial flap reconstruction of nasal defects between January 2015 to April 2018 with flap perfusion were assessed by ICG angiography.

Exposures

Indocyanine green angiography was performed to assess melolabial flap perfusion at second stage surgery after temporary clamping of the pedicle and after pedicle division and flap inset.

Main Outcomes and Measures

Flap perfusion in relation to a reference point on the cheek was calculated after both pedicle clamping and division by 2 methods: (1) ingress (arterial inflow) and egress (venous outflow) flap-to-cheek ratio; (2) flap-to-cheek perfusion (fluorescence) ratio at 3 time points (midpoint of ICG flap inflow, maximum [peak] fluorescence, and midpoint of ICG outflow), and their calculated mean. Correlations of perfusion with time between stages, and patient factors were performed; perfusion parameters after temporary pedicle clamping and after division and flap inset were compared.

Results

Ten patients (mean [SD] age, 66 [7.5] years) were enrolled with a mean (SD) interval of 23 (4) days between first and second surgery. No correlation existed between perfusion parameters and time interval between first and second stage, or any other patient factors. Of the different perfusion parameters, a statistically significant difference was observed when comparing temporary clamping and postdivision mean (SD) flap-to-cheek perfusion ratio (0.89 [0.22] and 0.80 [0.19]; 95% CI, 4.1-12.6; P = .001), as well as mean (SD) peak perfusion ratio (0.81 [0.2] and 0.77 [0.2]; 95% CI, 0.005-0.080; P = .02) only. No partial or complete flap necrosis was reported after pedicle division.

Conclusions and Relevance

Indocyanine green angiography is an effective method to determine neovascularization perfusion of melolabial flaps, with a mean perfusion of 89% after pedicle clamping. Future applications of this technology include use in patients at high risk for flap necrosis, or those who may benefit from early flap division to ensure adequate perfusion and minimize the time interval between staged procedures.

Level of Evidence

NA.

Determination of baseline alveolar mucosa perfusion parameters using laser Doppler flowmetry and tissue spectrophotometry in healthy adults

Objectives: To determine the baseline perfusion parameters of the alveolar mucosa using laser Doppler flowmetry and tissue spectrophotometry (LDF-TS) in healthy adults.Material and methods: Forty-two healthy adult subjects of either sex were tested. The perfusion of the alveolar mucosa was evaluated using a laser Doppler flowmetry and tissue spectrophotometry using O2C 'oxygen to see' device. The measurements encompassed the maxillary and mandibular mucosa at 20 different points.Results: The O2C device is a reliable method for noninvasive measurement of different perfusion parameters of the oral mucosa. The hemoglobin saturation values (So2 in %), as well as relative amount of hemoglobin in arbitrary units (AU) of the maxillary mucosa demonstrated lower values of that in the mandible. The flow value (AU) exhibited a significant difference in the posterior molar region only, while the velocity value (AU) showed a significant difference across all points except for the anterior region.Conclusion: the present study provides a set of brand-new perfusion parameters of the microcirculation of the alveolar mucosa using LDF-TS. The study suggests a variation of the perfusion parameters between the maxilla and the mandible. Differences in the anatomy of the blood supply, the thickness of the mucosa and the cortical bone, may be attributed to this variation. Further studies using different probes and a combination of ultrasonic measurements and SDF imaging will aid in giving a better overview of the perfusion in the oral mucosa.

In vivo perfusion of free skin flaps using extracorporeal membrane oxygenation

BACKGROUND

The vessel-depleted, irradiated, and frozen neck, as well as severe atherosclerosis of recipient vessels represent challenging problems in free flap transfer. Extracorporeal free flap perfusion theoretically allows free flap reconstructions in the absence of local donor vessels, but is associated with a number of technical issues. In this study, a novel technique is presented using a commercially available system for extracorporeal membrane oxygenation (ECMO), modified for small blood volumes.

METHODS

After preclinical testing, an ECMO system certified for lung support was used to establish blood flow through the flap's artery with oxygenation, decarboxylation and warming of diluted packed blood cells. Venous blood was allowed to flow passively into a separate container. Perfusion was performed for 15 min at intervals of 4 h over 4-6 days.

RESULTS

Five patients with soft tissue defects requiring free flap reconstruction were included. Either primarily thinned anterolateral thigh (ALT) flaps (n = 3) or radial forearm flaps (n = 2) were used. We observed infection of the perfusate, with consequent subtotal flap loss, in one patient, complete epithelial loss in two patients, venous congestion in one case, and almost uneventful healing in the fifth patient. With conservative wound care and a split thickness skin graft in one case, stable wound coverage was achieved in all patients except one, who had secondary healing. None of the patients required a second flap for sufficient coverage.

CONCLUSIONS

The technique described is associated with the risks of infection, flap congestion, nutritive hypoperfusion, and consequent tissue loss. Nevertheless, stable defect closure seems to be achievable even in patients with depleted recipient vessels.

Effects of topical negative pressure therapy on perfusion and microcirculation of human skin

BACKGROUND

Topical negative pressure wound therapy (TNPWT) is one of the most frequently used techniques in wound treatment. But some of the underlying mechanisms still remain unclear. One possible explanation is an improved microcirculation by TNPWT.

OBJECTIVE

This study investigated the influence of TNPWT on microcirculation on intact skin in real-time.

METHODS

In healthy individuals, we performed a combined tissue - laser/photo - spectrometry technique to monitor changes of 4 different microcirculation parameters in real-time: The local blood flow, the capillary-venous oxygen saturation, the blood flow velocity and the relative amount of hemoglobin. We compared these parameters using two different protocols: a continuously (VAC ON 60/OFF 60) and discontinuously (VAC ON 30/OFF 60/ON 5) application.

RESULTS

Our results demonstrate a significant increase of all four measured parameters during the active TNPWT and the pressure free period. The comparison of two different protocols shows an advantage of the examined parameters using a discontinuous TNPWT application.

CONCLUSIONS

Our study demonstrated the changes of the microvascular tissue perfusion in intact human skin under the conditions of negative pressure and may thereby offer a broader understanding of mechanisms underlying the TNPWT.

Laser Doppler Flowmetry to Differentiate Arterial From Venous Occlusion in Free Tissue Transfer

Purpose

The differentiation of arterial versus venous occlusion in free tissue transfers has rarely been described. This study investigated changes in blood flow caused by arterial and venous occlusion and the potential for laser Doppler flowmetry to distinguish between these 2 conditions for better clinical assessment and management of free tissue transfer.

Methods

Six patients with a mean age of 43.5 years underwent microsurgical free tissue transfer. The venous and arterial blood flow of the vessels and skin flap were monitored using laser Doppler flowmetry with high-frequency pulsed Doppler transducers for vessels and skin before, during, and after clamping the vessels for 10 minutes.

Results

The average decreases in blood flow in the artery and vein caused by clamping were 94.4% and 93.8%, respectively. On average, arterial occlusion demonstrated a sudden drop of 67.7% and venous occlusion caused a decrease of 26.6% on laser Doppler flowmetry in free tissue skin.

Conclusion

Using a vessel-holding probe, laser Doppler flowmetry could be used to differentiate between arterial and venous occlusion in free tissue transfer, thereby aiding decision-making for better clinical management.

Use of Near-infrared Spectroscopy and Implantable Doppler for Postoperative Monitoring of Free Tissue Transfer for Breast Reconstruction: A Systematic Review and Meta-analysis

BACKGROUND

Failure to accurately assess the perfusion of free tissue transfer (FTT) in the early postoperative period may contribute to failure, which is a source of major patient morbidity and healthcare costs. This systematic review and meta-analysis aim to evaluate and appraise current evidence for the use of near-infrared spectroscopy (NIRS) and/or implantable Doppler (ID) devices compared with conventional clinical assessment (CCA) for postoperative monitoring of FTT in reconstructive breast surgery.

METHODS

A systematic literature search was performed in accordance with the preferred reporting items for systematic reviews guidelines. Studies in human subjects published within the last decade relevant to the review question were identified. Meta-analysis using random-effects models of FTT failure rate and STARD scoring was then performed on the retrieved publications.

RESULTS

Nineteen studies met the inclusions criteria. For NIRS and ID, the mean sensitivity for the detection of FTT failure is 99.36% and 100% respectively, with average specificity of 99.36% and 97.63%, respectively. From studies with sufficient reported data, meta-analysis results demonstrated that both NIRS [OR = 0.09 (0.02-0.36); P < 0.001] and ID [OR = 0.39 (0.27-0.95); P = 0.04] were associated with significant reduction of FTT failure rates compared with CCA.

CONCLUSIONS

The use of ID and NIRS provided equivalent outcomes in detecting FTT failure and were superior to CCA. The ability to acquire continuous objective physiological data regarding tissue perfusion is a perceived advantage of these techniques. Reduced clinical staff workload and minimized hospital costs are also perceived as positive consequences of their use.

Pervasive wearable device for free tissue transfer monitoring based on advanced data analysis: clinical study report

Free tissue transfer (FTT) surgery for breast reconstruction following mastectomy has become a routine operation with high success rates. Although failure is low, it can have a devastating impact on patient recovery, prognosis, and psychological well-being. Continuous and objective monitoring of tissue oxygen saturation (StO2) has been shown to reduce failure rates through rapid detection time of postoperative vascular complications. We have developed a pervasive wearable wireless device that employs near-infrared spectroscopy (NIRS) to continuously monitor FTT via StO2 measurement. Previously tested on different models, the results of a clinical study are introduced. Our goal for the study is to demonstrate that the developed device can reliably detect StO2 variations in a clinical setting: 14 patients were recruited. Advanced data analysis was performed on the StO2 variations, the relative StO2 gradient change, and the classification of the StO2 within different clusters of blood occlusion level (from 0% to 100% at 25% step) based on previous studies made on a vascular phantom and animals. The outcomes of the clinical study concur with previous experimental results and the expected biological responses. This suggests that the device is able to correctly detect perfusion changes and provide real-time assessment on the viability of the FTT in a clinical setting.

Monitoring of Myocutaneous Flaps by Measuring Capillary Glucose and Lactate Levels: Experimental Study

INTRODUCTION

In surgery, certain defects require reconstruction with a microsurgical flap. The free flap failure rate varies between 2% and 5%. Vascular thrombosis is the most frequent complication and represents 15% to 73% of failures. The success rate of salvage therapy is greater when salvage surgery is early. Currently, clinical monitoring is the criterion standard but many noninvasive or minimally invasive techniques have been developed to improve early diagnosis of complications of vascular thrombosis. The aim of our experimental study was to compare clinical assessments with measurements of capillary glycemia and lactatemia during the monitoring of free flaps.

MATERIALS AND METHODS

Myocutaneous latissimus dorsi flaps with skin paddles were created in pigs under general anesthesia. For each animal, 2 flaps were created (right and left) using the same technique. Four groups were made: group 1 (no flap ligation: control group), group 2 (flap with permanent ligation of the artery), group 3 (flap with permanent ligation of the two veins), group 4 (flap with transient ligation of the artery and 2 veins for 1 hour). The postoperative monitoring protocol consisted of monitoring the clinical, biological (glucose and lactate), and histological parameters.

RESULTS

Eight animals were operated on and sixteen flaps were created. Each flap was clinically and biologically tested 25 times. Clinical, biological, and histological monitoring showed significant variations between the groups. The analysis of variance of capillary glycemia and lactatemia showed statistically significant difference between control group and group 2 (P < 0,0001), group 3 (P < 0,0001), or group 4 (P < 0,0001). There were no histological abnormalities after transient ligature at different times contrary to permanent ligature.

DISCUSSION-CONCLUSION

Measuring capillary levels of lactate and glucose associated with clinical monitoring may shorten the time to diagnosis of flap failure. Ultimately, this will save lives and achieve better functional and aesthetic results.

The Liver and Small Intestine Can Partly Compensate Severe Normovolemic Hemodilution in a Rat Model

BACKGROUND

Knowing the individual critical hematocrit for every organ is essential in operative scenarios in which extensive blood losses are expected. In the past, experimental settings were very heterogeneous resulting in the publication of widely differing values even for one organ in the same species. This study aimed to investigate the compensatory capacity of the liver and the small intestine in a rat model of severe normovolemic hemodilution.

MATERIALS AND METHODS

Male rats were subjected to a stepwise hemodilution with a succinylated gelatin-containing solution to a final hematocrit of 10%, being observed for additional 150 min. During the course of the experiment, blood glucose and L-lactate, as well as D-lactate and intestinal fatty acid-binding protein-2 measurements, were performed eight times in total. The amino acids alanine and glutamine were measured during dilution and at the end of the experiment (four times in total). Hemodilutional effects on the blood and oxygen supply of the liver and the small intestine were measured in a minimally invasive manner.

RESULTS

In the liver and the small intestine, there were no substantial changes in the blood flow of the microcirculation. Plasma glucose and lactate levels rose transiently, whereas lactate values did not exceed the upper threshold of aerobic metabolism. Plasma levels of the amino acids alanine and glutamine rose significantly and stayed elevated, whereas D-lactate and intestinal fatty acid-binding protein-2 were not significantly increased at any point during the whole experimental time compared to the initial value.

CONCLUSIONS

Severe hemodilution with a succinylated gelatin-containing solution is tolerated at a profoundly low hematocrit value of 10% during the experimental phase of 150 min.

Skin Microcirculatory Changes in Relation to Arteriovenous Fistula Maturation

Maturation of arteriovenous fistula (AVF) involves complex vascular remodeling. In this study, we evaluated the changes of skin microvascular perfusion over the extremity with AVF maturation using the laser Doppler fluximetry (LDF). A total of 45 patients with chronic kidney disease, Stages IV-V, were included; they had undergone AVF creation from July 2014 to June 2016 at our institute. The measurement of skin microvascular perfusion was accomplished proximal and distal to the fistula anastomosis site: pre- and post-operative day 1, week 2, week 6, and week 12. Thirty-two patients with mean age of 55.6 had achieved AVF maturation. There were 40.6% radial-based and 59.4% brachial-based AVF. There was a 32.8% reduction of mean skin perfusion distal to the fistula by day 1 compared to the baseline perfusion; however, perfusion increased 47% by week 2 compared to day 1 and no dramatic change was subsequently noted. There was an increase of mean skin perfusion, proximal to fistula anastomosis, over 12 weeks with 35.8% at day 1 from the baseline. However, the changes of the mean skin perfusion were not statistically significant. There was no significant relation of skin perfusion changes with the type of fistula, diabetes mellitus, hypertension, and hyperlipidemia. LDF successfully detected the subclinical change of skin microvascular perfusion in relation to AVF creation. Reduction of skin perfusion distal to the fistula suggests that in patients with existing perfusion inadequacy of extremities, they may experience ischemic symptoms as early as day 1 postoperation, and require close monitoring for distal limb ischemic-related complications.

Outcomes in microvascular head and neck reconstruction in the setting of restricted residency hours

BACKGROUND

Resident duty hour restrictions can limit the frequency of resident flap checks at smaller institutions with "home" call. Institutions are compensating with adjuvant nursing flap checks as well as incorporating technology; however, this management remains controversial.

METHODS

A prospective cohort of 122 free flaps for reconstruction of the head and neck by a single surgeon. Demographic information, operative details, postoperative care, and flap outcomes were recorded.

RESULTS

Over 42 months, 122 free flaps were performed on 115 patients. The overall flap success rate was 96%. The flap success rate at 72 h was 98% and 96% at the time of discharge with reexploration rates of 11.6%. The intraoperative and postoperative salvage rates were 71% and 64.3% respectively.

CONCLUSION

Limited resident flap checks combined hourly nurse flap checks and an implantable Doppler is an effective monitoring protocol for academic programs in the setting of residency duty hour restrictions.

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.

Evaluation of a Novel System for Hypothermic Oxygenated Pulsatile Perfusion Preservation

Background

Recently, a novel innovative machine perfusion (MP) system for hypothermic oxygenated pulsatile perfusion called the Airdrive (AD) has been developed. The aim of the study was to evaluate the biological safety of the AD system for perfusion preservation of kidney grafts in a porcine autotransplantation model using the low-viscosity perfusion solution Polysol (PS) in comparison with cold storage (CS) using PS or the University of Wisconsin solution (UW). In addition, we evaluated real-time microcirculation parameters. At sacrifice, grafts were retrieved for histological analysis and immunohistochemistry

Methods

After assessment of the microcirculation, left kidneys were retrieved. Following the washout, kidneys were preserved for 20 hr using AD-PS, CS-PS or CS-UW. Thereafter, contralateral kidneys were removed followed by heterotopic autotransplantation of the preserved graft. Seven days after transplantation animals were sacrificed with retrieval of the grafts for histological analysis. Renal function, renal microcirculation and tissue injury including the proliferative response of tubular epithelial cells (TECs) were compared.

Results

Preservation using AD-PS or CS-PS resulted in higher microcirculatory flow compared with CS-UW. Improved recovery of renal function was seen in the AD-PS and CS-PS groups compared with CS-UW. Structural integrity was better preserved using AD-PS compared with both CS groups. Proliferative response of TECs was higher in CS-UW preserved grafts compared to grafts preserved using AD-PS.

Conclusion

This study demonstrates the biological safety of the AD system in a porcine autotransplantation model. Also, the microcirculation was better preserved and less morphological injury was observed after 20 hr MP compared with CS.