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Implantable Optical Oxygen Monitor to Diagnose Flap Compromise
Mohamed M. Ibrahim, MD1, Zi Jun Wu, BS1, Hysem Eldik, BS1, Kristen Helton, PhD2, Natalie Wisniewski, PhD2, Bruce Klitzman, PhD1.
1Duke University Medical Center, Durham, NC, USA, 2profusa, INC, South San Francisco, CA, USA.

PURPOSE:
Surgical flaps experience perfusion-compromise in the immediate-postoperative-period. Early identification and correction of ischemia improves salvage. Current oxygen-monitoring-techniques are difficult. We developed a novel-approach to monitor tissue-oxygenation using implantable-optical-sensors, and correlated to loss of flap-viability.
METHODS:
Sensors made by incorporating benzo-porphyrin dye into poly(2-hydroxy-ethylmethacrylate). Sensors were ~3mm-long,1.5mm-wide,0.5mm-thick. Male-Sprague-Dawley-rats had the planned-skin-flap outlined on rat-dorsum and three-sensors were intradermally-implanted at tip,middle and base of impending flap. Three-sensors were implanted as controls laterally. Inspired-O2 was modulated from 100% to 12%. One-day-later,flap was elevated. Gross-flap-viability assessed with planimetric-analysis. Readings from sensors obtained by measuring decay-rate of phosphorescence following transdermal-excitation of O2-sensitive-fluorophore on days 0,3,7-postoperatively. Sodium-fluorescein injected to identify perfusion.
RESULTS:
Oxygen readings by sensors modulated as expected when inspired-oxygen changed, confirming sensors responsiveness/sensitivity. Gross-analysis showed ~16%-necrosis at tip of flap on d3 and was more-pronounced on d7. Sodium-fluorescein-analysis showed progressively decreased-perfusion in tip of flap, becoming significantly evident on d7(*p<0.05) with ~70%-flap-viability. Readings from flap-sensors showed significant-decreases in oxygenation in all-regions at all-time-points compared to control-sensors. Further-regional-analysis showed that sensors detected significant-decrease in oxygenation in tip of flap in comparison to base at all-time points(*p<0.05).
CONCLUSION:
Flap-oxygenation was assessed using novel sensors. Our sensors were able to detect significant-decreases in oxygenation immediately after creating flap. Regional-analysis showed that the decrease was more pronounced at tip of flap where necrosis later developed, making continuous-oxygen-measurement more sensitive in predicting flap-viability.


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