Noninvasive tissue oximetry has proven to be an extremely valuable tool to assist in the surgical decision-making process during various stages of autologous tissue breast reconstruction, in both the intraoperative and postoperative setting. Tissue oximetry is a sensitive measure of real-time changes in local tissue oxygen saturation (StO ₂ ). It is useful for intraoperative assessment of flap physiology, perforator selection, mapping to assist in the selection of tissue with the best chance of survival, and in identifying circulatory compromise during postoperative flap monitoring.

Although any monitoring technique serves as an adjunct to clinical evaluation, improvements in monitoring technologies can provide information in many cases that identify a problem before it becomes obvious on clinical evaluation. Flap salvage is inversely proportional to the time interval between the onset of ischemia and its clinical recognition. With this in mind, and with the availability of objective data from newer flap assessment technologies, monitoring and evaluation of a flap with information other than clinical observation has become even more relevant in optimizing outcomes in autologous breast reconstruction. Successful monitoring should provide rapid detection of vascular problems and be simple to use.

Autologous breast flap monitoring techniques currently employed include laser Doppler flowmetry, internal and external thermometry, internal and external Doppler monitoring, pulse oximetry, transcutaneous oxygen monitoring, quantitative fluorescein fluorescence, fluorescent angiography, and near infrared spectroscopy (NIRS). The most useful monitoring technique would be noninvasive, sensitive, accurate, quantitative, and provide continuous information. Techniques that are currently the most popular include the external Doppler, the implantable Doppler, and near infrared spectroscopy. The external Doppler technique is limited in its ability to reliably access the recipient vessels. The implantable Doppler technique has the ability to evaluate flow in both the arterial and venous system. Partial occlusions require clinical interpretation of the Doppler sounds. Additionally, accidental dislodgement of the probe leads to loss of signal. Fluorescent angiography is a new technique that provides reliable information regarding flow into the flap but provides only a snapshot in time consistent with the injection of a dye. The equipment is bulky and is neither designed for nor practical for postoperative flap monitoring.

Tissue oximetry using near infrared spectroscopy is a noninvasive technique for flap monitoring and evaluation. The technique readily lends itself to continuous monitoring of the tissue. Because of the easy placement of the sensor, different areas of the flap can be evaluated intraoperatively in real time during flap elevation and transfer. In addition, noninvasive near infrared tissue oximetry can be used to evaluate the viability of mastectomy skin flaps and assist in surgical decision making. Clinically, in many situations, such as in deeply pigmented skin or bruised mastectomy flaps, the evaluation of the mastectomy skin flap has proven to be a difficult clinical decision.

How does one come to trust and rely on a new monitoring device? First, there is the recognition that such a device would be useful. This recognition is basically an acknowledgment of our human limitations. Next, one must have some understanding of how the technology works and what the information represents. Normal physiology of a revascularized flap and abnormal physiology must be recognized. Lastly, when a level of confidence is gained, additional uses of the device can be applied to help evaluate the health and potential viability of a flap or piece of tissue.

Motivation for use of a continuous monitoring device after free flap transfer can be for a variety of reasons. Well-educated paraprofessionals, especially in the private-practice arena, are often relied upon to evaluate the viability of a flap. In a university setting it is most often the resident’s responsibility for flap evaluation. With overworked staff and reduced numbers of staff, the need for adjunctive monitoring is apparent.

Khouri reported in 1992 that the single most important factor in determining success of free tissue transfer was the experience of the surgeon. He reported a thrombosis rate of 3.7% with a 66% salvage rate for timely operative revisions. He also noted that most surgeons of that era relied on clinical observation alone as their method of monitoring a flap. Three years later, Hirigoyen reported from a questionnaire sent to 211 microsurgery centers that in 90% of cases adjunctive monitoring devices were used and that only 10% of surgeons rely solely on clinical evaluation for flap monitoring.

In 2010 Smit and colleagues conducted a literature review of flap monitoring methods over the last decade. They concluded that although clinical monitoring of a flap is inexpensive, their results do not favor this as the sole method of flap monitoring because of the longer response time to diagnose vascular compromise. In comparing near infrared spectroscopy, the implantable Doppler, and laser Doppler flowmetry, they concluded that near infrared spectroscopy has the greatest potential in becoming the ideal monitoring method. They reported that flap monitoring with near infrared spectroscopy was reliable and had 100% positive and negative predictive values.

Although the success rate for free flap transfer in the hands of most experienced microsurgeons is 95% or better, there is a take-back rate for vascular compromise in 6% to 25% of cases. Successful salvage of these take backs is much dependent upon the time interval from the onset of the event to its correction. Therefore, earlier recognition of vascular compromise is paramount for an ultimately high success rate in free tissue transplantation.

Near infrared spectroscopy for monitoring of autologous breast reconstructions has been studied in the author’s practice using the ViOptix T.Ox Tissue Oximeter ( Fig. 1 ) manufactured by ViOptix, Inc (Fremont, CA, USA) in 505 consecutive free flap breast reconstructions. Flaps used were either abdominal flaps (deep inferior epigastric perforator [DIEP] or superficial inferior epigastric perforator [SIEP]) or gluteal flaps (superficial gluteal artery perforator [s-GAP]). Monitoring began in the operating room and continued for a period of 36 hours postoperatively. The study group consisted of 305 patients with 135 single breast reconstructions, 170 bilateral breast reconstructions, and 30 patients who had 2 flaps used to make a single larger breast. Results of some of these reconstructions have been published in 2 previous articles. The ViOptix T.Ox Tissue Oximeter has been improved multiple times over the last 5 years. The current model being used includes a calculation, display, and alarm for the rate of drop of the tissue oxygen saturation, has dual channels to monitor 2 flaps simultaneously, and incorporates Wi-Fi. Wi-Fi allows the surgeon to check on the flap remotely using any device that has an Internet connection and browser. This feature allows the surgeon to interpret a trend without having to rely on a report from an observer in the hospital.

( A ) The ViOptix T. Ox Tissue Oximeter displays StO ₂ in real time and graphically displays its trend. There are alarms for the StO ₂ and rate of drop of StO ₂ . ( B ) The monitor cable is connected to a sensor that attaches to the tissue to be monitored with the supplied adhesive pad. The sensor is 1 cm in size and has 2 emitters and 4 light detectors.

( Courtesy of ViOptix Inc, Fremont, CA; with permission.)