Answer:
The most recent addition to the free flap monitoring advances is the laser Doppler, which measures cutaneous blood flow by Doppler flowmetry. In a study from 1996, laser Doppler was used to detect changes in different types of flaps (free TRAM, lat dorsi, and iliac crest osteomyocutaneous flaps) and showed that there is a general trend for skin blood flow to increase by 500-900% at 50-80 hours post-op before decreasing back to a previous baseline. These changes in skin blood flow over time, which can be followed continuously with laser Doppler measurements, depict the dynamic nature of skin blood flow and allow predictive patterns to be established, instead of a single “normal” value, by which to assess adequate flap perfusion. In addition to changes over time, and differences in the measurements of different donor muscles, there was also a study in 1998 which revealed that the oxygenation of tissues in young healthy individuals can vary enormously depending on the donor site. So in the scapula, oxygenation was as high as 50%, and as low as 15% in the lateral calf. Regional oxygen supply on different free flap donor sites varies significantly and needs to be taken into account with intracutaneous and transcutaneous measurements of pO2.