Plastic Surgery Research Council
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PSRC 60th Annual Meeting
Program and Abstracts

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Novel Implantable Optical Oxygen Monitor to Detect Flap Viability
Mohamed M. Ibrahim, MD, Bruce Klitzman, PhD.
The Division of Plastic and Reconstructive Surgery, Department of Surgery, Duke University School of Medicine, Durham, NC, USA, Durham, NC, USA.

PURPOSE:
Skin flaps are commonly used to manage complex surgical defects. Vascular compromise most commonly occurs in the immediate postoperative period. It is estimated that 6-25% of skin flaps require secondary surgical procedure and 10% fail. Early identification and correction of flap perfusion compromise dramatically improves probability of salvage. Therefore, it is critically important to optimize postoperative flap monitoring.
Serafin and Georgiade showed that flap oxygen tension is a good monitor that can call attention to compromised flaps. However, current techniques for continuous oxygen monitoring are difficult, expensive, technically challenging, and require constant air-tight probe attachment to flap. Other standard of care methods have limitations such as inconsistency and difficult calibration rendering them less-useful. We have developed a novel approach to monitor tissue oxygenation in skin flaps using new technology, and we have correlated tissue oxygenation measurements to flap viability.
METHODS:
Experimental sensors were made by incorporating benzo-porphyrin dye into a matrix of poly(2-hydroxy-ethylmethacrylate) that has interconnecting 40micron pores. These sensors were approximately 3mm-long, 1.5mm-wide, and 0.5mm-thick. Male Sprague-Dawley rats had the skin flap site outlined and three sensors were intradermally implanted at tip, middle and base of the impending flap. Three sensors were intradermally implanted as controls lateral to flap site at corresponding locations. Inspired O2 modulation from 100% to 12% confirmed sensor sensitivity. One day later, the outlined, caudally-based, full thickness flap was elevated on dorsum of rats. Gross flap viability was assessed with computer planimetric analysis. Readings from sensors were obtained on days 0,3 and 7 postoperatively using IVIS imaging system. Sodium-fluorescein was injected and analyzed on the corresponding days.
RESULTS:
Oxygen readings by sensors modulated as expected when inspired oxygen was changed, indicating that the sensors are responsive and sensitive. Gross planimetric analysis showed that 16% of the flap was necrotic at the tip of the flap as measured on d3 and was more pronounced on d7. Sodium-fluorescein analysis has demonstrated progressively decreased perfusion in the tip of the flap that started on d0 to become significantly evident on d7 (*p<0.05) with overall ~70% flap viability. Readings from the flap sensors have demonstrated statistically significant decrease in oxygenation in all regions of the flap at all time points compared to the control sensors. Further regional analysis has demonstrated that the sensors were able to detect significant decrease in oxygenation in the tip of the flap in comparison to the base at all time points (*p<0.05).


CONCLUSION:
Flap oxygenation was assessed using novel implantable O2 sensors. Sodium-fluorescein analysis detected significant flap necrosis not earlier than 7 days making it superior to gross planimetric analysis. Our sensors were able to detect significant decrease in oxygenation immediately after creating the flap. The regional analysis showed that the decrease was more pronounced at tip of the flap where necrosis later developed in the subsequent days, making continuous oxygen measurement more sensitive in predicting flap viability.


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