Near-infrared Spectroscopy for Monitoring Tissue Oxygenation in Breast Reconstruction

After a complex resection for breast cancer (e.g. mastectomy), a microvascular flap reconstruction can be used to fill up the tissue defects. A deep inferior epigastric artery perforator (DIEP)-flap is one of the most used microvascular flap reconstructions. Skin and fat from the abdomen are used to reconstruct a new breast.The success ratio of this type of surgery is high, more than 95%. Nevertheless, free flap failure can have disastrous consequences.The flap can be injured by surgical factors such as vascular complications.This is one of the major concerns and it usually occurs in the first hours after surgery. The success rate of the free flap depends on the continuous arterial inflow and the venous outflow through the new microvascular anastomoses. Thrombosis, kinking or external compression on the micro- and macrovascular blood vessels can cause necrosis of the flap. It is essential to recognize these complications as fast as possible to maximize the potential for flap salvage. Physical examination is still the gold standard for flap monitoring. However this monitoring is subjective, labor intensive and requires experience. Because of these disadvantages, a more objective method is desirable. In this suggested project, the flap will be monitored with FORE-SIGHT ELITE monitor( CAS Medical Systems incorporated) during the first 72 hours postoperatively. In this period most complications occur. The FORE-SIGHT ELITE Absolute Tissue Oximeter is a non-invasive device that measures absolute tissue oxygen saturation. It operates on the principle that blood contains hemoglobin in two primary forms, oxygenated hemoglobin (HbO2 ) and de-oxygenated hemoglobin (Hb), which absorb near-infrared light in different, measurable ways.The FORE-SIGHT ELITE incorporates CAS Medical Systems exclusive technology to project harmless near-infrared light in five precise wavelengths (690, 730, 770, 810 and 870 nanometer). An algorithm analyzes the reflected wavelengths. The algorithm is specially designed for the tissue with attention to unique characteristics of the tissue. Reflected light is captured by detectors positioned on the sensor for optimal signal collection. After analyzing the reflected light, the FORE-SIGHT ELITE displays the tissue oxygen saturation level on the monitor as an absolute number and provides a graphical representation of historical values.The FORE-SIGHT ELITE has been validated to determine cerebral tissue oxygen saturation amongst other in brain surgery. Tissue oxygen saturation (StO2) levels are determined by the ratio of oxygenated hemoglobin to total hemoglobin at the microvascular level (arterioles, venules, and capillaries) in the region to which the sensor is applied. This technique is called Near Infrared Spectroscopy (NIRS).Validated use of NIRS would be a major advantage to detect ischaemia in DIEP flaps. In the study pediatric sensor size is used to ensure proper depth of light penetration in a limited operating zone. By application of small neonatal sensors ( Foresight®-sensors (CASMED, Branford, CT, USA), on unilateral or bilateral DIEP flaps,light penetrates at 1.25cm depth.This reflects the perfusion and the oxygen consumption in the free flap.

A control pediatric sensor is placed on the abdomen where tissue is taken to perform the DIEP flap. This sensor reflects the normal tissue oxygenation of the patient. NIRS uses this technology for the detection of ischemia and hypoxia. It is a real-time, continuous, non-invasive method.