1 Corresponding author, ENT and Head and Neck Surgery,
plastic operations, SLK Kliniken Heilbronn, Heilbronn, Germany, OrcidID:
0000-0001-9319-8260, l.fiedler@gmx.at
2 University of Heidelberg, Faculty of Medicine,
Heidelberg, Germany
3 Department of Neurology, Klinikum Rechts der Isar,
Medical Faculty, Technical University of Munich, Munich, Germany,
houda.daaloul@caire.ai
4 Caire Health AI GmbH, Neherstraße 1, c/o TUM
Venturelabs, 81675 München
Keywords: Cutaneous Perfusion assessment, assessment, Flap, flaps,
perfusion, monitoring
Abstract
This paper provides a comprehensive analysis of modern techniques used
in the assessment of cutaneous flaps in reconstructive surgery. It
emphasizes the importance of preoperative planning and intra- and
perioperative assessment of flap perfusion to ensure successful
outcomes. Despite technological advancements, direct clinical assessment
remains the gold standard. We categorized assessment techniques into
non-invasive and invasive modalities, discussing their strengths and
weaknesses. Non-invasive methods, such as Acoustic Doppler Sonography,
Near-Infrared Spectroscopy, Hyperspectral Imaging Thermal Imaging, and
remote-Photoplethysmography, offer accessibility and safety but may
sacrifice specificity. Invasive techniques, including Contrast-Enhanced
Ultrasound, Computed Tomography Angiography, Near-Infrared Fluorescence
Angiography with Indocyanine Green, and Implantable Doppler Probe,
provide high accuracy but introduce additional risks. We emphasize the
need for a tailored decision-making process based on specific clinical
scenarios, patient characteristics, procedural requirements, and surgeon
expertise. It also discusses potential future advancements in flap
assessment, including the integration of artificial intelligence and
emerging technologies.
Introduction
In cutaneous reconstructive surgery, we count on different workhorses.
Depending on the extent of the defect, the reconstructive ladder in
Plastic surgery is used for evaluation and method selection. This ladder
starts with the primary closure, followed by the free skin grafts, local
flaps, pedicled flaps and ends with free flaps. [1, 2] A skin graft
does not have its vascular supply, whereas a flap is always connected to
a vascular system. [3] Flaps can be of different supply patterns and
are regularly used for defect reconstruction in larger skin and
subcutaneous defects.
Best medical care needs preoperative planning and peri- and
postoperative assessment of flap perfusion. A key to successful
reconstructive surgery is the necessity for preoperative planning and
intra- and postoperative assessment of flap perfusion to limit necrosis
or flap loss. [4] Preoperative flap planning has evolved in recent
times. In the past, flap planning was based on surgical and anatomical
landmarks and flap proportions. However, modern techniques, such as the
use of CT-angiography that enables perforator mapping as well as
pre-/and intraoperative assessment, have enhanced surgical outcomes in
individual cases. [5, 6] Despite progressive medical and technical
developments, there is currently no available method that permits a
uniform, simple, valid and cost-effective flap perfusion assessment. The
gold standard methods mainly rely on the surgeon’s clinical assessment
[7, 8], which involves observation of skin colour, temperature of
the flap, capillary refill, and bleeding pattern [7, 9, 10].
Similarly, surgical re-exploration is a valid way to clinically assess
perfusion, especially in the case of local and pedicled flaps. [11]
In an era of rapid technological advancement, as the field of
reconstructive surgery continues to evolve, it becomes imperative for
the surgeon to navigate through a multitude of technical solutions for
assessing flap perfusion without feeling inundated. It is essential to
possess a discerning understanding of when and how each method proves
effective, is economically viable, and possesses the necessary
sensitivity to genuinely inform clinical decisions in flap surgery.
This paper aims to furnish a thorough analysis of modern techniques
employed in the assessment of flaps in cutaneous surgery. For this
paper, we classify investigative modalities as non-invasive and
invasive. Any necessary insertion of contrast medium, probes or needles
into the patient is classified and treated here as an ”invasive” method.
Surgical anatomy and physiology of the
skin
As demonstrated in Figure 1, the skin (cutis) consists of two layers of
different thicknesses, the epidermis and the dermis. [12] Underneath
are subcutaneous tissue, fascia and muscle. [13] The epidermis
comprises the covering epithelial layer, this is also where skin colour
is controlled by the density of the resident melanocytes, while the
dermis is the carrier of the vascular/nerve supply and collagen fibres.
The superficial part of the epidermis is interlocked with the dermis via
the stratum papillare so that a tangential displacement of these layers
is not possible in a separable way. [12] In this respect,
displacements and thus, flap mobilization takes place in the subcutis.
While the subcutis can be prominent in terms of thickness in regions
such as the cheek, there are areas such as the eyelids or the auricular
anterior surface, as well as the lateral columella, where this layer is
virtually absent. [12] The vessels of the skin consist of two
vascular plexuses parallel to the surface, which serve not only for
supply but also for thermoregulation. The superficial Plexus is located
at the border between the reticular and papillary dermis. The deeper
plexus is located between the cutis and subcutis. Both vascular systems
are connected by vertical vessels. [12, 14]Mostly on muscles, larger
defined arteries (with their accompanying veins) run parallel to the
skin surface and send vertical vessels (in addition to vessels from the
subdermal plexus) to the skin. Examples here are the superficial
temporal artery [15], the supraclavicular artery [16] and the
angular artery [17]. From these defined vessels, axial pattern flaps
can be formed, i.e. those flaps that are supplied from a defined
subdermal vessel. [14]