New model for in vivo quantification of microvascular embolization, thrombus formation, and recanalization in composite flaps

Multiple pedicled flaps cover for large defects following resection of malignant tumors with partition concept

Large defects after skin malignant tumors resection were difficult to repair. We introduced a partition concept, in which the large defects were divided into several subunits, and each subunit was repaired by a certain pedicled flap to achieve a complete coverage.Between May 2012 and Oct 2016, 8 patients with skin malignant tumors underwent radical resection. Prior to surgery, the dimension of the potential defect after tumor ablation was estimated and outlined. After evaluation, the partition concept was applied and the defects were divided into several subunits. Also, the rationality of the choice of pedicled flap was evaluated. Each flap was used to cover its specific subunits defect.After excision, the defect areas were from 13 × 17 cm to 36 × 23 cm. Each subunit was designed to be repaired with a pedicled flap, which included local random flap, superficial iliac artery flap, transverse rectus abdominis myocutaneous (TRAM) flap, lateral thoracic advanced island flap, anterolateral thigh (ALT) flap, anteromedial thigh (AMT) flap, and deep circumflex iliac artery (DCIA) flap. Primary closure of both donor and recipient sites was achieved in all patients. All the flaps survived. Flap necrosis was not observed.Reconstruction of large defects following resection of malignant tumors with multiple pedicled flaps was a reliable method. The partition concept is useful in the reconstruction of large tumor wounds in 1-stage operation.

Paradoxical effects of heme arginate on survival of myocutaneous flaps

Ischemia reperfusion injury (IRI) contributes to partial flap and solid organ transplant failure. Heme-oxygenase 1 (HO-1) is an inducible, cytoprotective enzyme which protects against IRI in solid organ transplant models. Heme arginate (HA), a HO-1 inducer, is a promising, translatable, preconditioning agent. This study investigated the effects of preconditioning with HA on the clinical outcome of a myocutaneous IRI model. Forty male Lewis rats were randomized to intravenously receive 1) Control-NaCl, 2) HA, 3) HA and tin mesoporphyrin (SnMP), a HO-1 inhibitor; and 4) SnMP alone. Twenty-four hours later, an in situ transverse rectus abdominis myocutaneous flap was performed under isoflurane anesthesia. Viability of flaps was measured clinically and by laser-Doppler perfusion scanning. In vitro work on human epidermal keratinocytes (HEKa) assessed the effects of HA, SnMP, and the iron chelator desferrioxamine on 1) cytotoxicity, 2) intracellular reactive oxygen species (ROS) concentration, and 3) ROS-mediated DNA damage. In contrast to our hypothesis, HA preconditioning produced over 30% more flap necrosis at 48 h compared with controls (P = 0.02). HA-containing treatments produced significantly worse flap perfusion at all postoperative time points. In vitro work showed that HA is cytotoxic to keratinocytes. This cytotoxicity was independent of HO-1 and was mediated by the generation of ROS by free heme. In contrast to solid organ data, pharmacological preconditioning with HA significantly worsened clinical outcome, thus indicating that this is not a viable approach in free flap research.

In situ transverse rectus abdominis myocutaneous flap: a rat model of myocutaneous ischemia reperfusion injury

Free tissue transfer is the gold standard of reconstructive surgery to repair complex defects not amenable to local options or those requiring composite tissue. Ischemia reperfusion injury (IRI) is a known cause of partial free flap failure and has no effective treatment. Establishing a laboratory model of this injury can prove costly both financially as larger mammals are conventionally used and in the expertise required by the technical difficulty of these procedures typically requires employing an experienced microsurgeon. This publication and video demonstrate the effective use of a model of IRI in rats which does not require microsurgical expertise. This procedure is an in situ model of a transverse abdominis myocutaneous (TRAM) flap where atraumatic clamps are utilized to reproduce the ischemia-reperfusion injury associated with this surgery. A laser Doppler Imaging (LDI) scanner is employed to assess flap perfusion and the image processing software, Image J to assess percentage area skin survival as a primary outcome measure of injury.

Local Heat Shock Priming Promotes Recanalization of Thromboembolized Microvasculature by Upregulation of Plasminogen Activators

OBJECTIVE

Thromboembolization and subsequent microvascular perfusion failure is implicated in the pathology of a variety of diseases, including transient ischemic attack (TIA), stroke, and myocardial infarction, and also for the complications after interventional and microsurgical procedures in coronary heart disease and peripheral arterial occlusive disease. In vitro heat shock priming has been suggested to induce plasminogen activators, which are the major upregulators of the fibrinolytic system. Herein, we determined whether local heat shock priming endogenously upregulates plasminogen activators also in vivo, and whether this promotes recanalization of thromboembolized microvasculature.

METHODS AND RESULTS

To induce thromboembolization, a suspension of preformed microthrombi (maximum diameter: 40 microm) was injected via the femoral artery into the left hindlimbs of anesthetized rats. Local heat shock priming (42.5 degrees C, 30 minutes) was performed 24 hours before embolization and resulted in a significant increase of endothelium-derived plasminogen activator expression. The study of the microcirculation by intravital microscopy revealed in all tissues analyzed (muscle, periosteum, subcutis, and skin) that heat shock priming significantly (P<0.05) accelerates recanalization of the thromboembolized microvasculature when compared with nonprimed and sham-primed controls. Importantly, the addition of plasminogen activator inhibitor-1 to the microthrombi suspension completely blunted the heat shock-induced acceleration of microvascular recanalization.

CONCLUSIONS

Heat shock induces endogenous hyperfibrinolysis by upregulation of plasminogen activators that promote recanalization of thromboembolized microvasculature.

Mechanical mechanisms for thrombosis in microvessels

The hypothesis that thrombus can be induced in curved vessels due to mechanical stimuli was tested both experimentally and computationally. Our in vivo experiments on the mesentery of Sprague-Dawley rats (250-300 g) showed that thrombi were formed in non-injured curved microvessels (post-capillary venules, 20-50 micrometer in diameter), and they were initiated at the inner side of the vessel. We observed thrombus formation in 7 out of 32 microvessels after they were stretched and curved for 10-60 mm. To investigate the mechanical mechanisms of thrombus induction, we performed 3-D computational simulation using commercial software, FLUENT. The blood flow was approximated as a Newtonian laminar flow with Reynolds number around 0.01 in this type of microvessels. We considered the vessels with different curvatures (90 degrees and 180 degrees) as well as different shaped-cross sections (circular and elliptic). Computational results demonstrated that the shear rate and shear rate gradient and at the inner side of the vessel were higher than those at the opposite side. The differences became larger in more bended and elliptic-shaped microvessels. This suggested that higher shear rate and shear rate gradient are two of the factors that initiate the thrombosis in curved post-capillary venules. Our results are consistent with others in branched venules.