Comparative analysis of tissue fluorescence as related to capillary perfusion in random pattern skin flaps

Skin-sparing mastectomy

Background

Skin-sparing mastectomy (SSM) is a new technique being used in a variety of clinical settings. This article reviews the published data on SSM to establish its current role in clinical practice.

Methods

A Medline search was carried out using the key words ‘skin-sparing mastectomy’ to identify English-language articles published between 1990 and 2004 and further material referenced in these publications.

Results

SSM is most commonly used for surgical prophylaxis and to treat in situ and early invasive disease in patients who request immediate breast reconstruction. SSM and non-SSM result in similar surgical and oncological outcomes, but skin flap ischaemia is more common after SSM and is associated with a range of risk factors, including smoking.

Conclusion

SSM has become an established procedure in breast surgery, but there is a lack of prospective data on which to make evidence-based decisions about its use in individual patients.

In Vivo Visualization of Platelet/Endothelium Cell Interaction in Muscle Flaps

Increasing evidence underlines the substantial pathophysiological impact of platelets on the development of ischemia/reperfusion injury (I/R) in flaps. Methods for studying dynamic platelet mechanisms in flaps in vivo are not available. The aim of this study was to develop a model enabling quantitative analysis of platelet kinetics and platelet-endothelium cell interaction within the microcirculation of muscle flaps in vivo. Balb/c mice (n = 16) were anesthetized, and an epigastric muscle flap was prepared. Autologous platelets were separated from blood donor animals (n = 16) and labeled ex vivo by means of rhodamine-6-G. After I/R (90 minutes' clamping, 10 minutes' reperfusion), the platelets were administered intra-arterially (i.a.). Microhemodynamics and kinetics of platelets were investigated by intravital fluorescence microscopy. I/R of muscle flaps induced disturbances in microcirculation. The number of rolling platelets, as well as platelets adhering to the inner vessel wall of venules, was increased in the ischemia group. Using intravital fluorescence microscopy, platelet kinetics were analyzed directly in flap microcirculation in vivo for the first time. Since platelet/endothelial cell interaction is a key event in the pathophysiology after microsurgical procedures, this model will help to understand basic molecular mechanisms of platelet behavior during I/R.

Reliable assessment of skin flap viability using orthogonal polarization imaging

Intraoperative evaluation of skin flap viability has primarily been dependent on clinical judgment. The purpose of this study was to determine whether an orthogonal polarization spectral imaging device could be used to accurately predict viability of random-pattern skin flaps. Orthogonal polarization spectral imaging is a newly developed technique that visualizes the microcirculation using reflected light without the use of fluorescent dyes and allows for noninvasive real-time observation of functional microvascular networks. In Sprague-Dawley rats (n = 24), three types of random skin flaps were designed with unknown zones of viability (n = 8 per group). After flap elevation, the skin flaps were evaluated by both clinical examination and orthogonal polarization spectral imaging. Areas of the flap determined to be nonviable by clinical examination were measured and marked. Orthogonal polarization spectral imaging was subsequently performed, and areas of the skin flap with stasis (i.e., cessation of red blood cell movement) in the dermal microcirculation on orthogonal polarization spectral imaging were measured and marked. The skin flaps were then secured in place. Flaps were evaluated on a daily basis for clinical signs of ischemia and necrosis. On postoperative day 7, the total amount of random skin flap necrosis was measured and recorded. Clinical examination of the random skin flaps significantly underestimated the actual amount of eventual flap necrosis, and as result was a very poor predictor of flap necrosis. By contrast, assessment of microcirculatory stasis using the orthogonal polarization spectral imaging device correlated well with the subsequent development of necrosis in all groups. In the three groups, the average amount of flap necrosis predicted by clinical examination deviated from actual necrosis by approximately 2 to 4 cm. However, the amount that orthogonal polarization spectral imaging differed from actual necrosis was 0.1 to 0.3 cm. Therefore, orthogonal polarization spectral imaging was an excellent predictor of eventual flap necrosis and much more accurate than clinical observation (p < 0.001). Intraoperative evaluation of axial and random pattern flap viability has traditionally been based on clinical examination as no other reliable, convenient test currently exists. The authors demonstrated that an orthogonal polarization spectral imaging device accurately predicts zones of necrosis in random pattern flaps by directly visualizing cessation of microcirculatory flow. Intraoperative stasis in the dermal microcirculation correlated precisely with subsequent flap necrosis. Orthogonal polarization spectral imaging was significantly more accurate than clinical examination, which consistently underestimated flap necrosis. The orthogonal polarization spectral imaging technique may have value in the intraoperative assessment of skin flap perfusion such as that required after skin-sparing mastectomy.

In vivo monitoring of microvessels in skin flaps: introduction of a novel technique

Orthogonal polarization spectral (OPS) imaging was validated against intravital fluorescence microscopy (IFM) for microvascular measurements in skin flaps of hairless mice. Examinations were performed 1, 6, and 24 hours after elevation (n = 8) with both OPS imaging and IFM. A fluorescent dye was a prerequisite for IFM measurements but not for OPS imaging. Our findings show that OPS imaging can visualize the skin flap microcirculation independent from the application of fluorescent tracers. From these images, quantitative analysis of functional capillary density (FCD) was feasible. As expected, FCD was significantly lower in the distal part of the flap compared with its base (171.8 +/- 34.7 versus 62.0 +/- 25.6, mean +/- SD; 1 hour data). Comparison of OPS imaging and IFM revealed a significant correlation of FCD values (P < 0.001) at all time points. Given the success of this validation study on mouse skin flaps, clinical investigations will have to prove that OPS imaging can also successfully be used to monitor flaps in humans.

Perfusion imaging of skin island flap blood flow by a scanning laser-Doppler technique

Conventional laser-Doppler perfusion measurements can only obtain information from a single site. Since superficial blood flow is heterogeneous, this is a serious limitation, particularly in studies of methods to improve skin flap survival. A scanning laser-Doppler instrument has been developed which provides both an image and quantitative information about perfusion of the superficial tissue. We have evaluated this instrument in a circumflex iliac artery island flap model in the pig. The validity of the model was demonstrated by fluorescein dye injection and histology. Elevation of flaps was found to increase proximal flap blood flow but to decrease it in the distal portion. In flaps subjected to arterial ischaemia (9 h) and reperfusion we found an early increase in proximal flow, which gradually extended distally over the first 40 to 60 min. 16 h later, flow had declined, compatible with reperfusion damage to the vasculature. We suggest that perfusion imaging may be a valuable technique for investigating the mechanisms and extent of reperfusion injury.

In vivo analysis of microvascular reperfusion injury in striated muscle and skin

The use of intravital fluorescence microscopy in the models of the hamster dorsal skin fold chamber and the ear of the hairless mouse allows for the quantitative analysis of post-ischemic microvascular reperfusion injury in striated muscle and skin. Prolonged periods of ischemia (4 hours in striated muscle and 6 hours in skin) are associated with 1) perfusion failure of nutritive capillaries at the onset of reperfusion (no-reflow) and 2) activation, accumulation and microvascular adherence of white blood cells, formation of reactive oxygen metabolites and release of potent mediators (leukotrienes, platelet-activating factor) with the consequence of increased microvascular permeability due to the loss of endothelial integrity, interstitial edema and cell damage (reflow-paradox). Prophylactic and/or therapeutic regimens may, therefore, include improvement of capillary perfusion by hemodilution, and inhibition of leukocyte adherence, radical formation and mediator release by appropriate counteracting compounds, including anti-oxidants, antibodies directed against adhesion molecules, leukotriene synthesis inhibitors and platelet-activating factor receptor antagonists.