Spectral analysis of photoplethysmograms from radial forearm free flaps

Photoplethysmography utilizes a green-light-emitting diode to transmit light into a tissue. Reflected light from hemoglobin in dermal capillary red blood cells is received by a photo detector and is analyzed as light intensity along a frequency spectrum. This method of analysis allows for the removal of "noise" above (stray light and alternating current [AC]) and below (room vibrations and respiratory motion) the peak signal (1 to 2 Hz) and results in a means to distinguish between perfused and nonperfused tissues.

Twenty-two of 30 consecutive radial forearm free flap (RFFF) patients were enrolled in an approved human studies protocol to collect descriptive data for RFFFs that were perfused, arterial occluded, and venous occluded. The protocol was performed following completion of flap elevation and prior to pedicle ligation, flap inset, and microvascular anastomoses. Six 90-second measurements per flap were obtained (n = 132), processed by fast Fourier transform (FFT), and analyzed by blinded reviewers to determine their state of perfusion. Signal was collected 5 minutes after the onset or release of individual vessel occlusion.

The reviewers' interpretations were compared with the status of the pedicle and analyzed for sensitivity (0.96), specificity (0.95), and positive predictive value (0.98).

FFT analysis of photoplethysmograms from RFFF patients provides an accurate and rapid means for determining RFFF pedicle vessel patency. Photoplethysmography may provide a clinically useful tool for postoperative perfusion monitoring of free flaps in the future.