Only few studies have currently examined the hemodynamics of free tissue transfer to correlate quantitative results with clinical and technical observations. The aim of this study was to further evaluate the free flap skin island temperature as a potential tool of postoperative flap monitoring as temperature monitoring is more reliable if environmental influences on tissue temperature are eliminated. Hypothesis: Differences between free flap Skin Island and healthy adjacent skin

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... correlate to the difference between free flap Skin Island and healthy adjacent skin temperatures. Methods: ClinicalTrials.gov NCT01235299. Prospective cohort study. 56 free flaps (24 latissimus dorsi flaps,11 ALT,10 parascapular, 9 DIEP, 1 serratus, 1 VRAM) in 56 patients (35 males, age 49±14yrs) were prospectively monitored from November 2009 to January 2011 using a regular digital infrared surface thermometer simultaneously to microcirculatory assessment using combined Laser-Doppler and photo spectrometry (Oxygen-to-see). Results: Free flap microcirculatory blood flow was 109±37arbitrary units [AU]. Adjacent skin capillary blood flow was 143±52AU. Free flap skin island temperature was 95.3±3.0°F. Temperature of adjacent skin was 96.6±1.9°F. We found a positive correlation between the percentaged difference of free flap and adjacent skin temperatures and percentaged difference of free flap skin island and adjacent skin capillary blood flow (p=0.001). Conclusion: Our hypothesis was confirmed. A 10% reduction of free flap skin island temperature compared to adjacent skin indicates a deterioration of flap microcirculation by 50%, if skin temperature of the adjacent skin remains the same. Trends in surface skin island temperature monitoring are found to correlate with microcirculatory blood flow. Eliminating environmental influences on temperature assessment by comparing the temperature of the skin island of the free flap to the temperature of the adjacent healthy skin makes free flap temperature monitoring more reliable in reconstructive microsurgery.