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On “Noninvasive Tissue Oximetry for Flap Monitoring: An Initial Study (J Reconstr Microsurg 2007;23:189–197)”
15 October 2008 (online)
We read with great interest the article by Dr. Keller reporting his initial experience using a near-infrared spectroscopy system in 30 patients undergoing autologous tissue perforator free flap for breast reconstruction. We would like to congratulate Dr. Keller on his work and comment on some points.
In reconstructive microsurgery, time is a critical determinant in flap revision surgery. The earlier the revision surgery, the better the reported outcome. In a total of 1142 free-flap procedures, 113 flaps were reexplored (9.9%) due to compromise. Ninety-three flaps (82.3%) presented with circulatory compromise within 24 hours; 108 (95.6%) had circulatory compromise within 72 hours, and 92 flaps (85.2%) were salvaged within this period. Unfortunately, flap compromise continues to occur even in the most experienced hands. Flap monitoring is therefore of utmost importance. Patients receiving microsurgical free flaps in the reported institution are referred to a microsurgical intensive care unit for 5 postoperative days. Flap monitoring is performed by a team of specially trained nurses who perform hourly checks of flap color, capillary refill, turgor, and temperature. Pinprick testing and evaluation of vascular flow by handheld Doppler ultrasonography devices are performed when a flap is clinically suspected of compromise. Any patient with clinically suspected flap compromise is evaluated by a senior resident, who in consultation with an attending physician makes the decision to take the patient to the operating room for reexploration.
Beyond the clinical and Doppler ultrasound evaluation of flaps, several additional monitoring tools have been introduced. As Dr. Keller pointed out, implantable Cook Doppler probes are associated with significant costs and limitations according to the vessel detected: Either venous or arterial compromise is detected with one probe only. Given these facts, a noninvasive, instantaneous monitor that is easy to use with a high reliability might be of additional value. For several years, both laser Doppler and near-infrared spectroscopy monitors have been reported and implemented for flap monitoring.   Tissue oxygenation measurement has been reported with a high correlation with positron emission tomography imaging among 10 patients suffering and neck squamous cell cancer with tumor resection and microsurgical free flap reconstruction.
Using a single oximetry system as done by Dr. Keller using the ODISsey Tissue Oximeter (ViOptix Inc., Fremont, CA), only tissue oxygenation is detected. As mentioned in the article, the measuring depth for the sensor used in the study was between 0 and 5 mm. We would appreciate Dr Keller's commenting on whether to expect changes in the tissue oxygenation at deeper layers, such as at 12 or 20 mm.
Another technical and practical challenge is the potential ambient light bias that might modify or interfere with the near-infrared spectroscopy system. We would be grateful if Dr Keller could also comment on how he achieved similar ambient light conditions during day- and nighttime in different environments (operating room, postanesthesia care unit, regular ward). Second, probe pressure might be of interest in this regard because various probe pressures might detect distinct tissue areas that might interfere with the results of a continuous reading as well. Inline technical parameters such as the intra- and interobserver reliability of a given monitoring system like the ODISsey Tissue Oximeter have to be reported to judge the additional value of the system.
Dr. Keller pointed out that sole oximetry might have problems in detecting venous congestion at the very beginning. The combination of laser Doppler flowmetry and spectroscopy might overcome this obstacle. The Oxygen-to-see system (LEA Medizintechnik, Giessen, Germany) combines both measures to detect three parameters of microcirculation in real time and noninvasively:
Capillary blood flow Tissue oxygen saturation Postcapillary venous filling pressures
Depending on the probes used, simultaneous measurement of 2- and 8-mm or 8- and 16-mm tissue depths is possible. The use of the system has been reported in 61 patients undergoing maxillofacial reconstruction with fasciocutaneous radial forearm flaps. Following anastomosis, blood flow and flow velocity exceeded the level before flap elevation and reached significant differences by the third postoperative day (p < 0.05). Oxygen saturation decreased significantly by the third postoperative day, and hemoglobin oxygenation showed stable values after performing anastomosis. Simultaneous, noninvasive laser Doppler flowmetry and tissue spectrophotometry detected vascular complications in all cases with no false-positive or false-negative results and before clinical assessment. We have reported the use of this combined laser Doppler and spectroscopy system for microcirculatory monitoring of buried flaps for complex periorbital reconstruction.
None of the monitoring just described has been tested in randomized controlled trials against, for example, clinical examination and/or duplex sonography for flap monitoring, however. We therefore do not know currently whether the additional information derived by these monitoring tools changes clinical practice in a way that revision surgery success rates exceed the current percentages with conventional clinical examination and/or duplex sonography. These randomized controlled trials are pending.
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Karsten KnoblochM.D. Ph.D.
Plastic, Hand and Reconstructive Surgery, Hannover Medical School
Carl-Neuberg-Str. 1, 30625 Hannover, Germany