Assessing flap perfusion: optical spectroscopy versus venous doppler ultrasonography.

OBJECTIVE: To use optical spectroscopy as a noninvasive method to monitor the viability of free flaps and to compare the near-infrared probe with the implantable venous Doppler ultrasound probe. DESIGN: Prospective, randomized series using an animal model. METHOD: Optical spectroscopy was used to measure variables that correlate with tissue perfusion and oxygenation. An epigastric artery island flap was raised in 20 rats. Vascular insults were simulated by clamping the vessels to the flap. Measurements were taken using near-infrared spectroscopy (NIRS) at the time of clamping and at 15, 30, 45, and 60 minutes of occlusion. The clamps were removed, and final NIRS measurements were taken. In the second experiment, a flap was raised in six rats, each of which underwent a series of short-lived occlusions. The occlusions were monitored with both NIRS and the implantable venous Doppler probe. RESULTS: In the first experiment, disruptions in flap perfusion resulted in significant changes in tissue hemoglobin oxygen saturation and total hemoglobin concentration as detected using NIRS. NIRS predicted vascular compromise with a sensitivity of 89.7% and a specificity of 97.9%. In the second experiment, NIRS predicted vascular compromise with a sensitivity of 63.3% and a specificity of 94.8%. The clinical assessment, based on recordings, yielded sensitivities and specificities of 70% and 94.8% (surgeon 1) and 71.7% and 94.8% (surgeon 2). CONCLUSION: Optical spectroscopy represents a reliable method of noninvasively monitoring free flaps. Further investigations as to the clinical utility of spectroscopy as an adjunctive monitoring device are currently being performed.

Assessment of skin flaps using optically based methods for measuring blood flow and oxygenation.

The objective of this study was to compare two noninvasive techniques, laser Doppler and optical spectroscopy, for monitoring hemodynamic changes in skin flaps. Animal models for assessing these changes in microvascular free flaps and pedicle flaps were investigated. A 2 x 3-cm free flap model based on the epigastric vein-artery pair and a reversed MacFarlane 3 x 10-cm pedicle flap model were used in this study. Animals were divided into four groups, with groups 1 (n = 6) and 2 (n = 4) undergoing epigastric free flap surgery and groups 3 (n = 3) and 4 (n = 10) undergoing pedicle flap surgery. Groups 1 and 4 served as controls for each of the flap models. Groups 2 and 3 served as ischemia-reperfusion models. Optical spectroscopy provides a measure of hemoglobin oxygen saturation and blood volume, and the laser Doppler method measures blood flow. Optical spectroscopy proved to be consistently more reliable in detecting problems with arterial in flow compared with laser Doppler assessments. When spectroscopy was used in an imaging configuration, oxygen saturation images of the entire flap were generated, thus creating a visual picture of global flap health. In both single-point and imaging modes the technique was sensitive to vessel manipulation, with the immediate post operative images providing an accurate prediction of eventual outcome. This series of skin flap studies suggests a potential role for optical spectroscopy and spectroscopic imaging in the clinical assessment of skin flaps.