MODULATED IMAGINING OF TISSUE TRANSFER FLAPS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Background & Purpose of Research Goals The goal of this proposed research project is to develop a protocol that would involve work already underway at the Beckman laser institute, using Diffuse Optical Spectroscopy (DOS) to evaluate changes in tissue transfer flaps. This project would build on the current animal studies investigating a pedicle skin flap model. The DOS device, developed at the Beckman Laser Institute in conjuncture with a partnership with Modulated Imaging Inc., allows for spatial determination of hemoglobin concentrations [Hb], degree of tissue oxygenation, and edema. This information and changes in the valves have been shown by other groups as means to monitor tissue transfer flaps and has been shown to precede changes noted clinically, thereby allowing for earlier detection of vascular compromise, and early intervention. This project proposes the development of a pig free flap animal model as well the development of a clinical research project that would use Modulated Imaging to monitor both pedicle and free flaps in the para-operative period in patients undergoing reconstructive surgery. The major goal would be to demonstrate that the use of this device allows for the early detection, differentiation between arterial and venous thrombosis, and thereby allows for early intervention and improved salvage rates in vascular compromised flaps. Laboratory & Clinical Background Thrombosis of either an arterial or venous nature is a major complication after tissue transfer in reconstructive surgery. It is known that generally venous thrombosis has a worse out-come, when compared to arterial thrombosis after reestablishment of blood flow, due to differences in the pathophysiology involved in venous congestion of the tissue and impaired oxygen delivery after reperfusion. The fact that venous thrombosis is more difficult to detect early may also contribute to the poor prognosis with venous thrombosis. Studies have shown that frequent monitoring of flaps allows for early detection of vascular thrombosis and thereby allows for early operative re-exploration, and improved salvage rates after vascular compromise. Free flap thrombosis rates requiring re-exploration have been reported in the literature as 5-10%, with flap loss rates reported as 3-5%, and post-operative thrombosis salvage rates have been reported as ranging from 40-69%. Several authors have emphasized that one of the keys to improving the salvage rate after graft thrombosis is frequent monitoring, in the early post-operative period, thus allowing for early recognition, and intervention, including operative re-exploration. Hjortdal et al. using a pig model demonstrated increased tissue necrosis after re-perfusion due to venous congestion compared to arterial ischemia, this is thought to be due to increased tissue fluid (i.e. venous congestion / edema) associated with venous thrombosis, which inhibits diffusion of oxygen through the interstitial space to the tissue. Payette et al. showed in an article published in Feb. 2005, that spectroscopy was more consistently reliable when compared to laser Doppler in detecting arterial flow problems in rat animal models, using both an epigastric free flaps model as well as a pedicle skin flap model (reverse McFarlane flap). Wolff et al. in 2006 reported using a single device that used spectroscopy in combination with laser Doppler flow to detect vascular complications prior to clinically evident changes in the tissue flaps, and was able to reliably distinguish between venous and arterial thrombosis, in patients undergoing maxillofacial reconstruction with a fasciocutaneous radial forearm free flaps. The use of DOS technology developed at the Beckman Laser Institute in conjuncture with Modulated Imaging Inc. may provide a useful technology in monitoring both pedicle and free tissue transfer flaps in the para-operative during the first 2-3 days after surgery when a majority of arterial and venous thrombosis occur. This monitoring of flaps using DOS may allow for early detection, and classification of vascular compromise prior to clinically evident changes, thereby improving salvage rates and thus cost in patients undergoing reconstructive surgery. Proposed Methodology Four part to study design, including: 1. Development of an animal model with both pedicle and free flaps designed to determine the changes in the [Hb], oxygen concentration, and tissue edema that would allow for a DOS device to reliably determine arterial vs. venous thrombosis, with reasonable sensitivity and specificity. 2. Develop a randomized, blinded study in which clinical observation is compared to application of a DOS device, in the detection of arterial and venous thrombosis, in an animal model. 3. Develop an experiment to determine if early detection of venous thrombosis using a DOS monitoring device, (prior to clinical detection) and reperfusion allows for improves salvage rates in flaps after venous thrombosis in an animal flap model. 4. Development of a prospective study that would collect data from patients undergoing both pedicle and free flaps designed to monitor tissue in the near post-operative period using both classical clinical monitoring in the ICU including conventional arterial Doppler signals, and as well as monitoring using a DOS device. This would be done during the first three days post-operatively, or until the patient is transferred out of an ICU level of care if done prior to post-operative day number 3.