Pulse oximetry and PPG measurements in plastic surgery

There is a need for a monitor of flap viability in plastic and reconstructive surgery. Pulse oximetry has been suggested as a suitable monitoring technique but commercially available oximeters have difficulty obtaining reliable readings from flaps. This may be due to an inappropriate range of LED currents for the thin flap tissue or to insufficient PPG amplitudes for signal processing. A system has been developed which uses previously described miniature, sterilizable probes to measure both the AC and DC PPG amplitudes at two wavelengths for a range of LED currents. Measurements were made from a variety of sites on normal subjects where a conventional pulse oximeter operates correctly. A second series of measurements were made from healthy tissue on patients undergoing plastic surgery, as a model of a healthy skin flap. The LED currents used on the flap model were within the range available to the pulse oximeter used. The AC PPG amplitudes from the flap model were significantly smaller than those obtained from intact tissue sites. Manual calculations of SaO₂ made using the PPG measurements from the flap model suggest that a dedicated oximeter with a specially adapted algorithm for flap measurements is feasible