Assessing flap perfusion: optical spectroscopy versus venous doppler ultrasonography

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.

Prospective, randomized series using an animal model.

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.

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).

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.