Postoperative monitoring of local and free flaps with contrast-enhanced ultrasound (CEUS)--analysis of 112 patients

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.

Pediatric Microsurgery and Free-Tissue Transfer

Advancements in microsurgery, along with increased microsurgical experience in pediatric patients, have made free-tissue transfer a reliable modality for pediatric bone and soft tissue reconstruction today. Free-tissue transfer is most commonly used in children for the coverage of large or complex defects resulting from traumatic, oncologic, or congenital etiologies. While flap success and complication rates between pediatric and adult populations are similar, special considerations must be taken into account within the pediatric population. In this article, we will describe common indications, technical nuances, and clinical considerations for the management of the pediatric free-tissue transfer patient.

Propeller Flaps of the Lower Extremity

Wounds of the lower extremity involving the distal third of the leg remain a significant challenge due to anatomic location and often poor host physiology. Perforator-based propeller flaps may provide rapid coverage of these wounds with a relatively low rate of major complications and often readily managed minor complications. A thorough vascular evaluation must be performed prior to the procedure to ensure adequate flap design and selection of the correct perforator is performed. They have the added advantage over their soft tissue free flap counterparts in that they have significantly less host morbidity with similar rates of total necrosis.

Contrast-Enhanced Ultrasound for Musculoskeletal Applications: A World Federation for Ultrasound in Medicine and Biology Position Paper

This World Federation for Ultrasound in Medicine and Biology position paper reviews the diagnostic potential of ultrasound contrast agents for clinical decision-making and provides general advice for optimal contrast-enhanced ultrasound performance in musculoskeletal issues. In this domain, contrast-enhanced ultrasound performance has increasingly been investigated with promising results, but still lacks everyday clinical application and standardized techniques; therefore, experts summarized current knowledge according to published evidence and best personal experience. The goal was to intensify and standardize the use and administration of ultrasound contrast agents to facilitate correct diagnoses and ultimately to improve the management and outcomes of patients.

Enhanced Resorption of Liposomal Packed Vitamin C Monitored by Ultrasound

Vitamin C is an essential nutrient for humans and is involved in a plethora of health-related functions. Several studies have shown a connection between vitamin C intake and an improved resistance to infections that involves the immune system. However, the body cannot store vitamin C and both the elevated oral intake, and the intravenous application have certain disadvantages. In this study, we wanted to show a new formulation for the liposomal packaging of vitamin C. Using freeze etching electron microscopy, we show the formed liposomes. With a novel approach of post-processing procedures of real-time sonography that combines enhancement effects by contrast-like ultrasound with a transducer, we wanted to demonstrate the elevated intestinal vitamin C resorption on four participants. With the method presented in this study, it is possible to make use of the liposomal packaging of vitamin C with simple household materials and equipment for intake elevation. For the first time, we show the enhanced resorption of ingested liposomes using microbubble enhanced ultrasound imaging.

Transcutaneous oxygen measurement using ratiometric fluorescence imaging as a valid method for monitoring free flap transplants

BACKGROUND

Reconstruction of soft tissue defects with free flaps is a common procedure in plastic and reconstructive surgery. Most postoperative complications occur within the first 48-72 hours after surgery. After postoperative complications, short perfusion restoration times may improve flap survival rates by up to 30-50%. Ratiometric fluorescence imaging is an additional or alternative method of postoperative flap monitoring.

OBJECTIVE

To test the efficacy and utility of transepidermal oxygen flux imaging to evaluate postoperative skin oxygenation of free and local flaps in the first 48 hours after surgery.

METHODS

The study included 32 patients (aged between 18 and 80 years; mean age 52.9) with a tissue defect covered with a free flap transplant at the Department of Plastic and Reconstructive Surgery of the University Medical Center Regensburg. Postoperative oxygen flux was measured with the 'VisiSens system' placed on the vascular pedicle as well as on the peripheral and central part of the flap.

RESULTS

Values of oxygen flux were higher in case of flap congestion (0.069±0.012) or flap necrosis (0.155±0.083) than in cases without any complications (0.061±0.006). Flux values of different areas of the same flap showed only minimal differences (central part: 0.065±0.008, peripheral part: 0.070±0.009, vascular pedicle: 0.056±0.004); the level of significance was p = 0.904.

CONCLUSION

Imaging transepidermal oxygen flux by ratiometric luminescence seems to be a reliable alternative, indirect method of postoperative flap monitoring with regard to microcirculatory function and flap viability.

Video Tutorial for Clinical Flap-Monitoring in Plastic Surgery

Supplemental Digital Content is available in the text.

Transepidermal oxygen flux measurement - First clinical application for postoperative wound monitoring

BACKGROUND

Measurement of skin oxygen is of great interest in diverse fields of medicine. Different pathologies, e.g. infection, ischemia cancer or chronic wounds show a characteristic oxygen distribution and skin oxygen tension. Additionally diverse operative procedures require a reliable postoperative monitoring in order to ensure success of the therapy.

OBJECTIVE

Aim of this study was to assess transepidermal oxygen flux for postoperative wound monitoring after operative treatment of fractures close to the hip.

METHODS

22 patients underwent transepidermal oxygen flux measurement at the first postoperative day. Transepidermal oxygen flux measurement was performed using ratiometric luminescence imaging. Examination was conducted in close proximity to the operation wound. The corresponding area at the contralateral side served as reference.

RESULTS

Oxygen flux in the operation area was higher (0.084±0.021) than the contralateral side (0.071±0.029).

CONCLUSIONS

Transepidermal oxygen flux imaging by ratiometric luminescence imaging seems to be a reliable tool to assess postoperative wound healing. However further investigations in greater populations and under pathologic conditions have to be performed to prove these first results.

Enhancing the role of paediatric ultrasound with microbubbles: a review of intravenous applications

Contrast-enhanced ultrasound (CEUS) represents a complementary technique to greyscale and colour Doppler ultrasonography which allows for real-time visualization and characterization of tissue perfusion. Its inherent advantages in the child makes ultrasonography an ideal imaging modality; repeatability and good tolerance along with the avoidance of CT, a source of ionizing radiation, renders ultrasonography imaging desirable. Although currently paediatric CEUS is principally used in an "off-label" manner, ultrasonography contrast agents have received regulatory approval for assessment of paediatric focal liver lesions (FLL) in the USA. The safety of ultrasound contrast-agents is well documented in adults, as safe as or even surpassing the safety profile of CT and MR contrast agents. Except for the established intracavitary use of CEUS in voiding urosonography, i.v. paediatric applications have been introduced with promising results in the abdominal trauma initial diagnosis and follow-up, characterization and differential diagnosis of FLL and characterization of lung, pleura, renal and splenic pathology. CEUS has also been used to detect complications after paediatric transplantation, evaluate inflammatory bowel disease activity and assess tumour response to antiangiogenic therapy. The purpose of this review was to present these novel i.v. paediatric applications of CEUS and discuss their value.