TISSUE PERFUSION MONITOR FOR FREE TISSUE TRANSFER

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The technique of free tissue transfer, has revolutionized many areas of reconstructive surgery, such as limb salvage and reconstruction of the esophagus, where other options have been unacceptable. As free tissue transfer is now being done routinely at institutions where inexperienced staff are unable to adequately monitor viability, the need for a reliable method to monitor the patency of microvascular anastomoses has become increasingly evident. Accurate and objective assessment of blood flow both at the time of surgery and during the post operative period is essential, because if the tissue viability is lost, the consequences can be staggering. Early recognition of postoperative vessel thrombosis is of utmost importance if reexploration is to prove successful. To this end, numerous monitoring techniques have been investigated. Those classified as direct monitors of perfusion have proven to be of little or no value - particularly as free flap monitors. Probes are bulky, very expensive, and require great care in positioning and removal. Indirect monitors such as those which monitor the tissue concentration of a physiological gas such as oxygen, rate ahead of the direct monitors due to advantages of low cost, simplicity, ease of placement and removal, etc. However, these monitors lack the needed specificity of the direct monitors for measuring tissue perfusion. Adding to this specificity problem is the fact that the sensor cannot be calibrated once it is implanted. Our approach is to preserve the simplicity afforded by indirect monitoring devices, while providing the specificity for tissue perfusion measurement, by utilizing a self-calibrating tissue PO2/PCO2 probe, which manipulates the local tissue gas conditions. Tissue PO2 and PCO2 are monitored under alternating depleting and nondepleting conditions. A physilogically based mathematical relationship relates tissue perfusion to the PO2 and PCO2 measurements. This proposal is directed toward the in vivo validation of the method.