The clinical application of IR

The clinical application of IR thermography was first introduced in 1956, and it was found that the skin temperature over a cancer in a breast was higher than that of normal tissue. With the advancements in IR camera technology featuring higher sensitivity and computer image analysis, it is suitable for measuring subtle changes in flap surface temperature. de Weerd and colleagues reported dynamic IR thermography used in autologous breast reconstruction with a DIEP flap. This noninvasive and noncontact technique for indirect monitoring of skin blood perfusion can be used in the preoperative planning and intraoperative evaluation of flap perfusion, as well as the postoperative monitoring of perfusion dynamics of DIEP flaps. Yamamoto and colleagues reported a handheld IR thermography camera for postoperative monitoring of the thoracodorsal artery perforator flap. The practical thermography camera weighs approximately 300 g, and thus it is quite easy to carry around for flap monitoring.
Near IR spectroscopy Near IR spectroscopy was first described to measure tissue oxygenation in 1977. Calibrated IR light was delivered to tissue via a light source probe, and a detector was also used to measure absorbed and scattered light at different wavelengths, which was influenced by the tissue chromophore, mainly through hemoglobin. By IR, we can measure relative changes of oxygenated, deoxygenated, and total Apoptosis Compound Library concentration, and oxygen saturation in tissue. Repez and colleagues reported a prospective study using a near IR spectroscope in 50 free flaps for breast reconstruction, and 10 flaps with circulatory compromise were all identified prior to clinical assessment. With venous thrombosis, deoxygenated and total hemoglobin increased whereas oxygenated hemoglobin and oxygen saturation decreased. With arterial thrombosis, deoxygenated total hemoglobin increased, whereas oxygenated hemoglobin, total hemoglobin, and oxygen saturation decreased. The oxygen saturation dropped to zero from baseline in mean 43 minutes with venous thrombosis and 37 minutes with arterial thrombosis. Keller reported 208 microsurgical flaps for breast reconstruction using near IR spectroscopy for postoperative monitoring. Tissue oxygen saturation <30% or a decrease rate of >20% per hour and sustained for >30 minutes was set as the positive finding for vascular thrombosis. Five out of 208 flaps with vascular compromise were all identified in this method before clinical signs became evident. In Steele\'s report, a comparison was made between conventional and near IR spectroscopy monitoring of free flap surgery. The overall survival of threatened flaps was zero (0/5) in the conventional group and 86% (6/7) in the near IR spectroscopy group (p < 0.005). The overall flap survival was 91% in the conventional group and 99% in the near IR spectroscopy group (p < 0.05). Lin and colleagues also reported a microsurgical breast reconstruction flap salvage rate of 58% with conventional monitoring method and a 94% rate with near IR spectroscopy (p = 0.015). Although near IR spectroscopy is a sensitive, specific, and noninvasive method for postoperative free tissue transfer monitoring, drawbacks remain and the main issue is the cost required for the monitoring device and disposable probes. Pelletier and colleagues performed a cost analysis of near IR spectroscopy for monitoring autologous free tissue breast reconstruction. The authors hypothesized that the practice will reduce medical costs by eliminating the need for specialized nursing. Although the costs for the monitoring device increased, the total cost for the patient decreased significantly in their study. In addition to IR spectroscopy, visible white light spectroscopy was also used for free flap monitoring by noninvasively measuring hemoglobin saturation at the capillary level. Fox and colleagues reported monitoring 31 free flaps with visible white light spectroscopy. Normal capillary hemoglobin saturation was between 40% and 75%. One flap was found to have vascular thrombosis, and hemoglobin saturation dropped from 50% to <30% 50 minutes prior to identification by clinical examination.