Name: in situ transverse rectus abdominis myocutaneous flap: a rat model of myocutaneous ischemia reperfusion injury
Uploaded: 2013-06-08T14:00:00
Description: Watch this Scientific Journal Video about In situ Transverse Rectus Abdominis Myocutaneous Flap: A Rat Model of Myocutaneous Ischemia Reperfusion Injury at JoVE.com

This work was funded by the Medical Research Council grant G1000299.
The corresponding author would like to thank Gary Borthwick, University of Edinburgh, for assisting during the surgery.
The authors would like to acknowledge advice from Helen Douglas and Iain Mackay and allowing us to observe their Deep Inferior Epigastric (DIEP) flap procedure (Canniesburn Plastic Surgery Unit, Glasgow Royal Infirmary, 84 Castle Street, Glasgow G4 0SF, UK).
The authors would also like to thank Gary Blackie at the University of Edinburgh for his help in producing the video for this article.

All surgery is performed in accordance with guidelines set out by the United Kingdom's Home Office and the University of Edinburgh's Veterinary Services Department.
1. Surgical Procedure Set-up Notes
<ol>
 <li>Change into clean surgical scrubs, gown, scrub cap and mask. Clean all surfaces of the operating room including equipment with 2% chlorhexidine in 70% isopropyl alcohol. </li>
 <li>Prior to surgery, autoclave all surgical supplies and instruments that will be used in the procedure. ...

Modifications and trouble shooting
The protocol presented here reproduces the IRI seen in free tissue transfer in an experimental system enabling further understanding of that process and provides a means to investigate means of ameliorating IRI and improving outcome. This could easily be modified to produce a more severe injury if it were based on the non-dominant, deep, inferior epigastric pedicle or if the ischemic time were increased. 
Limitations of technique
 <p...

The goal of this protocol is to demonstrate a reliable and reproducible model of the ischemia-reperfusion injury observed in free tissue transfer to enable interventional strategies to be investigated. 
Free tissue transfer is defined as the vascular detachment of an isolated block of tissue followed by autologous transplant of that tissue with anastomosis of the flap's transected vessels to native vessels at the recipient site. The procedure is known as FTT and the tissue being transferred referred to as the free flap.
Free tissue transfer is the gold standard approach for the correction of complex, composite defects where local options are unsuitable or unavailable.1-4 Ischemia reperfusion injury (IRI) is inevitable in free tissue transfer, contributes to flap failure5,6 and has no effective treatment. The elective nature of free flap surgeries permits administration of pharmacological agents to precondition against IRI. 
IRI results in impaired flow through the microcirculation by endothelial activation and metabolic dysfunction,7 increased capillary permeability and subsequent interstitial edema7, influx of inflammatory cells,8 release of inflammatory mediators, reactive oxygen species9 and complement deposition.10 This complex process of hypoxia and subsequent reperfusion injury ultimately leads to cell death. A model of myocutaneous IRI enables the effectiveness of preconditioning strategies on clinical outcomes to be assessed. Recent work has validated the use of animal models of IRI studies as a surrogate for human IRI by comparing the molecular changes observed in human subjects and existing animal data.10,11 
The rat transverse rectus abdominis myocutaneous (TRAM) flap was first described in 1987 in German12 and in 199313 in English. This model gained wide popularity13-25 as a cheap, robust model to investigate different strategies to reduce IRI associated with free tissue transfer.14,17-22 The majority of these studies were designed as unipedicled TRAM flaps based on the deep, inferior, epigastric vascular pedicle.15-18,20-22 Comparison of the data from these studies is complicated by the use of different sized cutaneous islands (10.5 - 30 cm2) and different lengths of postoperative follow-up (2 - 10 days). The average total percentage area flap necrosis in the control arm of these studies is 69 &plusmn; 6.2% (mean &plusmn; SEM). It should be noted that these six papers all employ the rectus abdominis muscle as a carrier for the vascular pedicle but do not expose, divide and microanastomose or clamp the vessels. Zhang et al.23 have described a true, free rat TRAM flap based on the superior epigastric vessels in which the flaps were raised, vessels divided and the myocutaneous flap transferred and microanastomosed to the groin vessels. This difficult technique required the microanastomosis of 0.45 - 0.5 mm caliber vessels. Only fifteen were performed and of these 67% survived.23 The model described by Zhang et al.23 is an excellent model for the human free TRAM flap as it truly mirrors the injury incurred during FTT. The other published models of a rat TRAM flap more accurately reflect the injuries incurred during a human pedicled TRAM but do not accurately reflect the IRI as these flap in do not undergo an ischemic period followed by reperfusion as the vascular pedicle is never clamped or divided and microanastomosis performed. This protocol and video describe a new model of free tissue transfer using the rat TRAM in which the IRI is replicated using microclamps. This more faithfully replicates IRI than the pedicle TRAM predecessors but is technically easier than performing the microanastomosis. Microclamps have been widely employed by transplant researchers to recreate IRI associated with solid organ transplant;26-33however, this is the first time it has been described in the rat TRAM flap.

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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.

Rat models are more economical than larger animals models,36 are disease-resistant in nature and may be genetically manipulated. Loose skinned animals, such as rodents, were thought to have a different arrangement of cutaneous blood supply compared to fixed skinned animals such as humans and pigs. In loose skinned animals, skin is supplied primarily by direct cutaneous blood vessels passing through the subcutaneous fat to the overlying skin (Figure 4) By contrast, fixed skinned animals derive...

Watch this Scientific Journal Video about In situ Transverse Rectus Abdominis Myocutaneous Flap: A Rat Model of Myocutaneous Ischemia Reperfusion Injury at JoVE.com

In situ Transverse Rectus Abdominis Myocutaneous Flap: A Rat Model of Myocutaneous Ischemia Reperfusion Injury

Free tissue transfer is widely employed in reconstructive surgery to restore form and function following oncological resection and trauma. Preconditioning this tissue prior to surgery may improve outcome. This article describes an in situ transverse rectus abdominis myocutaneous flap (TRAM) in rats as a means for testing preconditioning strategies.

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 ...

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