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Rapid Detection of Acute Vascular Occlusion Using Oxygen Monitoring in a Rat Myocutaneous Flap Model
Mohamed M. Ibrahim, MD1, Jennifer S. Chien, BSE1, Mahmoud M. Mohammed, B.Eng1, Timothy King, MD, PhD2, Bruce Klitzman, PhD1.
1The Division of Plastic, Maxillofacial, and Oral Surgery, Department of Surgery, Duke University School of Medicine, Durham, NC, USA, 2The Division of Plastic Surgery, Department of Surgery, University of Alabama, Birmingham, AL, USA.

PURPOSE:
Free tissue transfer requires close postoperative monitoring for vascular occlusion. Vascular compromise commonly occurs in the immediate postoperative period in association with failure of the micro-vascular anastomosis. The resiliency of tissue to hypoxia and ischemia is crucial to the success of the surgery. It is estimated that 6 percent to 25 percent of skin flaps require a secondary surgical re-exploration and approximately 10 percent of flaps fail. Currently, all monitoring methods have limitations because they require an experienced operator, suffer calibration difficulties and are expensive. Furthermore, many of these methods impose a significant delay between the time of vessel occlusion and its detection. In this study we introduce implantable oxygen sensors as a new method to detect acute vascular occlusion.
METHODS:
Experimental sensors were made by incorporating benzo-porphyrin dye into a matrix of biocompatible hydrogel. These sensors were approximately 3mm-long, 1.5mm-wide, and 0.5mm-thick. Male Sprague-Dawley rats were used throughout the study. Sensors were implanted intradermally in the impending flap site. Inspired oxygen was modulated between 100% and 12% to qualitatively confirm sensor sensitivity. Superficial inferior epigastric artery (SIEA) myocutaneous flaps were surgically elevated. The SIEA flap was first outlined on the shaved skin of the right ventral abdomen by placing a 3×5cm square template based on the location of the superficial inferior epigastric vessels. These vessels were carefully dissected to create a 3×5cm island flap containing skin, subcutaneous fat, and panniculus carnosus muscle. Tissue oxygen tension (TOT) readings were obtained from implanted sensors both at baseline and during vascular clamping of the feeding blood vessels.
RESULTS:
Tissue Oxygen Tension (TOT) measurements from the sensors were observed to modulate as expected by a magnitude that correlated with the changes in the inspired oxygen levels. Clinical observation of the flaps did not show any significant change in color and temperature of the flaps during or immediately after clamping of the feeding blood vessels. Real-time analysis of the sensors implanted in the myocutaneous flaps has demonstrated that acute vascular clamping of the feeding blood vessels in the pedicle were immediately detected within 70 seconds. (*p<0.05)
CONCLUSION:
Oxygen monitoring in tissues is highly sensitive and can be specific for the detection of acute vascular occlusion. This approach is superior to clinical observation, faster than current standard of care methods and offers a cost-effective, and accurate means of monitoring free tissue transfers.


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