Plastic Surgery Research Council

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Quantitative Tissue Oximetry in Simulated Venous Occlusion
Prasanth Patcha, MD, MEng1, Donald Browne, BS2, Hanzhou Li, BA2, Chien-Wei Wang, BS2, Kristina Falkenstrom, MD2, Jack Yu, MD, DMD, MS Ed, FACS, FADI2.
1University of Alabama at Birmingham, BIRMINGHAM, AL, USA, 2Medical College of Georgia, Augusta, GA, USA.

Background: Tissue oximetry for free flap monitoring is becoming more utilized in many institutions. Recently published studies have demonstrated improvement in flap salvage rates from 57% to 96% (2), with the understanding being that tissue oximetry can alert the surgeon to flap compromise hours before the skin paddle shows clinical signs of it. The same studies however, take note of the shortfalls of tissue oximetry, namely, obtaining reproducible and reliable readings, and then interpretation of results prompting re-exploration in the OR (4). We present our in-vivo simulation of venous congestion in tissue oximetry in hopes to better delineate early signs of flap compromise and tissue physiology.
Methods: Seventeen random subjects' baseline blood pressure and tissue oximetry readings on the upper extremity were obtained. The subjects' diastolic pressure was used to determine venous occlusion pressure, and a BP cuff was applied to that pressure on the arm(5). Tissue oximetry was recorded for a duration of 10-15 minutes. A linear mixed model was used to analyze the data.
Results: Tissue oximetry (StO2) levels fell in a predictable and reproducible manner across all subjects. The correlation between StO2 and time was analyzed with a linear mixed model, which suggested a significant decrease of StO2 with time (P<.0001). Specifically, the StO2 decreased 1.38 percent per minute on average (95%CI -1.51, -1.26) after the cuff was applied. Subjects with a smoking history and breast cancer history failed to demonstrate a significant difference among the group.
Conclusion: Our venous occlusion model provides a viable method to quantify the early venous occlusion process. A negative slope of 1.38%/min is highly significant for a venous outflow obstruction. This quantitative endpoint may elucidate when to plan for flap exploration. Further study is warranted to delineate differences that comorbidities and demographics impart.


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