The limitations of tissue-oxygen measurement and positron emission tomography as additional methods for postoperative breast reconstruction free-flap monitoring

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.

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.

Modern postoperative monitoring of free flaps

PURPOSE OF REVIEW

Flap failure in microvascular reconstruction is a costly complication with total flap loss being the worst-case scenario. With the aim to rapidly identify a postoperative circulatory problem, some susceptible flaps can be saved by careful clinical monitoring or by various technical monitoring methods. In head and neck surgery, where the flaps are often buried and difficult to monitor clinically, a reliable technical monitoring method would be useful. A broad range of different techniques are in use varying according to practical and personal preferences among clinics and surgeons. However, no evidence for any particular technique being superb has emerged. We review reports of some frequently used and modern free flap monitoring techniques.

RECENT FINDINGS

Clinical monitoring is still the gold standard to which other techniques are compared to. Laser Doppler flowmetry and near-infrared spectroscopy have been reported to identify early circulatory problems, but both techniques are not well suited for buried flaps. Implantable Doppler, flow coupler, partial tissue oxygen pressure and microdialysis are invasive monitoring methods suitable for buried flaps.

SUMMARY

More research with practical and clinically relevant parameters, that is flap salvage rate, false positive rate and cost-efficiency are needed before objective comparisons between different monitoring techniques can be made.

Oxygen Regulation in Development: Lessons from Embryogenesis towards Tissue Engineering

Oxygen is a vital source of energy necessary to sustain and complete embryonic development. Not only is oxygen the driving force for many cellular functions and metabolism, but it is also involved in regulating stem cell fate, morphogenesis, and organogenesis. Low oxygen levels are the naturally preferred microenvironment for most processes during early development and mainly drive proliferation. Later on, more oxygen and also nutrients are needed for organogenesis and morphogenesis. Therefore, it is critical to maintain oxygen levels within a narrow range as required during development. Modulating oxygen tensions is performed via oxygen homeostasis mainly through the function of hypoxia-inducible factors. Through the function of these factors, oxygen levels are sensed and regulated in different tissues, starting from their embryonic state to adult development. To be able to mimic this process in a tissue engineering setting, it is important to understand the role and levels of oxygen in each developmental stage, from embryonic stem cell differentiation to organogenesis and morphogenesis. Taking lessons from native tissue microenvironments, researchers have explored approaches to control oxygen tensions such as hemoglobin-based, perfluorocarbon-based, and oxygen-generating biomaterials, within synthetic tissue engineering scaffolds and organoids, with the aim of overcoming insufficient or nonuniform oxygen levels and nutrient supply.

Near-infrared imaging for the assessment of anastomotic patency, thrombosis, and reperfusion in microsurgery: a pilot study in a porcine model

BACKGROUND

Advances in microsurgical techniques have increased the use of free tissue transfer. Methods of intraoperative flap perfusion assessment, however, still rely primarily on subjective evaluation of traditional clinical parameters. Anastomotic thrombosis, if not expeditiously identified and revised, can result in flap loss with significant associated morbidity. This study aims to evaluate the use of near-infrared (NIR) fluorescence imaging in the assessment of microsurgical anastomotic patency, thrombosis, and vascular revision.

MATERIALS AND METHODS

A model of pedicle thrombosis was created using bilateral abdominal flaps isolated on deep superior epigastric vascular pedicles in four Yorkshire pigs. Following flap elevation, microvascular arterial and venous anastomoses were performed unilaterally, preserving an intact contralateral control flap. Thrombosis was induced at the arterial anastomosis site using ferric chloride, and both flaps imaged using NIR fluorescence angiography. The thrombosed vascular segments were subsequently excised and new anastomoses performed to restore flow. Follow-up imaging of both flaps was then obtained to confirm patency using fluorescence imaging technology.

RESULTS

Pedicled abdominal flaps were created and successful anastomotic thrombosis was induced unilaterally in each pig. Fluorescence imaging technology identified large decreases in tissue perfusion of the thrombosed flap within 2 minutes. After successful revision anastomosis, NIR imaging demonstrated dramatic increase in flow to the reconstructed flap, but intensity did not return to pre-thrombosis levels.

CONCLUSIONS

Early identification of anastomotic thrombosis is important in successful free tissue transfer. Real-time, intraoperative evaluation of flap perfusion, anastomotic thrombosis, and successful revision can be performed using NIR fluorescence imaging.

Evaluation of bone viability

Bone scintigraphy is an excellent tool to assess bone viability. The functional information provided is crucial in several clinical settings, like the detection of avascular necrosis, septic embolism, frostbite lesions and osteonecrosis, and to evaluate the results of surgical treatment in cases of avascular necrosis. Mechanisms to obtain molecular images, as well as different kind of techniques, are detailed. Comparative and multimodality imaging to focus on any clinical problem and a review of the clinical indications reflect the multidisciplinary approach with close collaboration between orthopaedists, radiologists and nuclear medicine physicians. Finally, an effort has been made to list the most important points of imaging of bone viability in children.

PET scanning in plastic and reconstructive surgery

In this report we highlight the use of PET scan in plastic and reconstructive surgery. PET scanning is a very important tool in plastic surgery oncology (melanoma, soft-tissue sarcomas and bone sarcomas, head and neck cancer, peripheral nerve sheath tumors of the extremities and breast cancer after breast esthetic surgery), as diagnosis, staging, treatment planning and follow-up of cancer patients is based on imaging. PET scanning seems also to be useful as a flap monitoring system as well as an infection's imaging tool, for example in the management of diabetic foot ulcer. PET also contributes to the understanding of pathophysiology of keloids which remain a therapeutic challenge.