Recent advances in postoperative free microvascular flap monitoring

Standardized Pre-clinical Surgical Animal Model Protocol to Investigate the Cellular and Molecular Mechanisms of Ischemic Flap Healing

BACKGROUND

Some of the most complex surgical interventions to treat trauma and cancer include the use of locoregional pedicled and free autologous tissue transfer flaps. While the techniques used for these reconstructive surgery procedures have improved over time, flap complications and even failure remain a significant clinical challenge. Animal models are useful in studying the pathophysiology of ischemic flaps, but when repeatability is a primary focus of a study, conventional in-vivo designs, where one randomized subset of animals serves as a treatment group while a second subset serves as a control, are at a disadvantage instigated by greater subject-to-subject variability. Our goal was to provide a step-by-step methodological protocol for creating an alternative standardized, more economical, and transferable pre-clinical animal research model of excisional full-thickness wound healing following a simulated autologous tissue transfer which includes the primary ischemia, reperfusion, and secondary ischemia events with the latter mimicking flap salvage procedure.

RESULTS

Unlike in the most frequently used classical unilateral McFarlane's caudally based dorsal random pattern skin flap model, in the herein described bilateral epigastric fasciocutaneous advancement flap (BEFAF) model, one flap heals under normal and a contralateral flap-under perturbed conditions or both flaps heal under conditions that vary by one within-subjects factor. We discuss the advantages and limitations of the proposed experimental approach and, as a part of model validation, provide the examples of its use in laboratory rat (Rattus norvegicus) axial pattern flap healing studies.

CONCLUSIONS

This technically challenging but feasible reconstructive surgery model eliminates inter-subject variability, while concomitantly minimizing the number of animals needed to achieve adequate statistical power. BEFAFs may be used to investigate the spatiotemporal cellular and molecular responses to complex tissue injury, interventions simulating clinically relevant flap complications (e.g., vascular thrombosis) as well as prophylactic, therapeutic or surgical treatment (e.g., flap delay) strategies in the presence or absence of confounding risk factors (e.g., substance abuse, irradiation, diabetes) or favorable wound-healing promoting activities (e.g., exercise). Detailed visual instructions in BEFAF protocol may serve as an aid for teaching medical or academic researchers basic vascular microsurgery techniques that focus on precision, tremor management and magnification.

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.

Performance of infrared thermography and thermal stress test in perforator mapping and flap monitoring: A meta-analysis of diagnostic accuracy

BACKGROUND

Accurate mapping of perforators prior to flap reconstruction and early detection of poor flap perfusion reduces the risk of flap failure. Infrared thermography (IRT) has recently regained popularity within reconstructive surgery to aid flap design, reduce operative time and assess flap viability based on surface temperature changes. The aim of this review is to quantify the diagnostic ability of IRT in perforator mapping preoperatively and monitor flap perfusion perioperatively.

METHODS

We conducted a systematic review of literature and included all studies that evaluated the use of IRT for perforator mapping and flap perfusion monitoring. We used a mixed-effects logistic regression bivariate model to estimate the summary sensitivity and specificity and constructed hierarchical summary receiver operative characteristic (HSROC) curves.

OUTCOME

We identified 18 studies and observed IRT to have sensitivities of 99.6% and 89.6% with specificities of 99.9% and 96.0% for perforator mapping and flap monitoring, respectively. Moreover, IRT recognises patterns of perfusion within interperforator zones through visualisation of angiosomal rewarming and may improve flap outcomes.

The use of venous anastomotic flow couplers to monitor buried free DIEP flap reconstructions following nipple-sparing mastectomy

Nipple sparing mastectomy with free tissue transfer for breast reconstruction offers excellent aesthetic outcomes but poses a challenge in monitoring the buried flap. Venous anastomotic flow couplers directly monitor buried flaps without the need for monitoring skin paddles. In a two year period we used the Synovis GEM™ flow coupler on 24 DIEP flaps. In our practice, flow couplers are effective in monitoring buried free flaps for breast reconstruction. The avoidance of a second procedure to remove a skin paddle improves patient experience and nullifies the additional flow coupler cost. One patient needed return to theatre when a Doppler wire became dislodged early in the series. There were no other issues with flap monitoring and no flap failures. We offer our tips to optimise flow coupler use.

A compact hyperspectral camera for measurement of perfusion parameters in medicine

Worldwide, chronic wounds are still a major and increasing problem area in medicine with protracted suffering of patients and enormous costs. Beside conventional wound treatment, for instance kinds of oxygen therapy and cold plasma technology have been tested, providing an improvement in the perfusion of wounds and their healing potential, but these methods are unfortunately not sufficiently validated and accepted for clinical practice to date. Using hyperspectral imaging technology in the visible (VIS) and near infrared (NIR) region with high spectral and spatial resolution, perfusion parameters of tissue and wounds can be determined. We present a new compact hyperspectral camera which can be used in clinical practice. From hyperspectral data the hemoglobin oxygenation (StO2), the relative concentration of hemoglobin [tissue hemoglobin index (THI)] and the so-called NIR-perfusion index can be determined. The first two parameters are calculated from the VIS-part of the spectrum and represent the perfusion of superficial tissue layers, whereas the NIR-perfusion index is calculated from the NIR-part representing the perfusion in deeper layers. First clinical measurements of transplanted flaps and chronic ulcer wounds show, that the perfusion level can be determined quantitatively allowing sensitive evaluation and monitoring for an optimization of the wound treatment planning and for validation of new treatment methods.

Managing vascular compromise of hand and digit replantation following traumatic amputation

Hands are anatomically complex and have great social, physical and emotional importance. Hand or digit replantation following traumatic partial or complete amputation is a complex injury for nursing staff to understand and manage. The absence of clear guidance, combined with a lack of consensus in the literature gives rise to ambiguity and insufficient understanding of appropriate and effective management. This article aims to outline nursing care of the patient in the first few days following hand or digit reattachment, particularly focusing on the recognition and management of arterial and venous compromise. Complications must be recognised and acted on quickly to give the best chance of survival so it is essential for nurses to have an accurate understanding of the signs, symptoms and management options of vascular compromise. Leech therapy, also discussed, has long been used as a nonsurgical option in the management of venous congestion and is a simple and minimally invasive method of managing congestion.

Detection of free flap pedicle thrombosis by infrared surface temperature imaging

BACKGROUND

Reliable detection of any circulatory issue threatening flap viability after free flap surgery is essential for prompt flap salvage. Currently, the gold standard of flap monitoring is clinical monitoring. However, this method presents logistical challenges to insufficient trained personnel. Auxiliary methods are becoming increasingly vital.

MATERIALS AND METHODS

Twelve swine pedicle myocutaneous flaps were harvested and monitored using infrared cameras to investigate the developed monitoring parameters and vascular thrombosis in the free flap model.

RESULTS

The mean flap surface temperature after vein or artery occlusion decreased significantly, but the differences were relatively small. As a result, the difference between recorded (flap surface temperature [T_s]) and predicted (estimated surface temperature [T_es]) flap surface temperature (ΔT = T_s- T_es) was used as the parameter for pedicle thrombosis. A ΔT of <0.86°C was used as a vascular occlusion criterion; the sensitivity and specificity of this parameter were 90% and 81%, respectively. The standard deviation of the surface temperature (SD_T) was another indicator of vascular occlusion; the estimated sensitivity and specificity for vessel occlusion of SD_T < 0.48°C were 84% and 73%, respectively.

CONCLUSIONS

Infrared thermal imaging has the advantages of being noninvasive, contact-free, continuous, and able to detect the whole flap surface area. Two indicators, ΔT and SD_T, can be used with high sensitivity and specificity for early prediction of flap pedicle thrombosis. Further human studies are necessary to validate clinical application of infrared thermal imaging.

Noninvasive Free Flap Monitoring Using Eulerian Video Magnification

Eulerian Video Magnification (EVM) can enhance subtle changes in videos to reveal what was once invisible to the naked eye. In this proof of concept study, we investigated using EVM as a novel form of free flap monitoring. Free flaps with skin paddles were filmed in the operating room with manipulation of their pedicles. In a representative 77-year-old female who received a latissimus dorsi-serratus-rib composite free flap, EVM was able to detect blockage of arterial or venous supply instantaneously, providing a visible representation through degree of color change in videos. EVM has the potential to serve as a powerful free flap monitoring tool with the benefit of being noninvasive, sensitive, easy-to-use, and nearly cost-free.