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

Abstract

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.

Keywords: flap monitoring; free flap; free tissue transfer; microsurgery; microvascular reconstruction; reconstructive surgery.

Figure 1

Illustrative comparison between young and aging skin. Age-related skin changes can manifest in various ways, thereby complicating free flap evaluation and concealing common signs of free flap failure. Externally, deep wrinkles, dark-pigmented age spots, and superficial vascular drawings reflect the senescence of the skin structures. On the histological level, the dermo-epidermal junction flattens and the fibrillar-connective structure collapses. Due to a progressive subcutaneous fat reduction, decrease in water content, and loss of elasticity the impression of youthful smooth skin vanishes over time.

Figure 2

The current gold standard and novel techniques in the postoperative monitoring of free flaps. To date, the combination of clinical examination and acoustic Doppler sonography is still considered the state of art to monitor free flaps. More specifically, the attending physician examines the free flap serially evaluating the flap temperature, turgor, color, and capillary refill. Typically, this cornerstone of free flap assessment is supported by acoustic Doppler sonography as an instrument to sound the blood flow and velocity. Accordingly, the gold standard is based on a hands-on approach with the active-practical involvement of the physician at periodic intervals. In recent years, a broad spectrum of novel technologies has been proposed to facilitate and refine free flap monitoring. These high-tech methods range from the well-known color duplex sonography through implantable Doppler systems to hyperspectral and thermal imaging. In contrast to the conventional approach, this new generation of monitoring tools relies on digital (remote) equipment that allows the biophysical flap condition to be assessed in a technologically advanced and automatic-computerized form.