Portable-Type Laser Doppler Flowmetry Monitoring for Free Tissue Transfers: Factors That Affects Free Flap Blood Flow

Laser Doppler flowmetry (LDF) is an established tool for monitoring free flaps, yet traditional devices are often bulky and difficult to interpret the value. We utilized portable LDF (pLDF), which is lightweight and allows for easier mobilization compared to conventional LDF systems. This study aimed to identify systemic factors affecting pLDF values to enable more objective clinical interpretation.

We retrospectively reviewed 65 free flaps in 64 patients over a 3-year period. All flaps were monitored using pLDF. A mixed-effects model was employed to explore factors influencing pLDF values.

Two flaps (2.9%) developed vascular compromise, one of which was successfully salvaged after emergency reoperation. Statistical analysis revealed that pLDF values were significantly influenced by mean blood pressure (mBP) and hemoglobin concentration (Hb). Specifically, every 1 mmHg increase in mBP resulted in a 0.098 mL/min increase in the pLDF value (p < 0.001), and every 1 g/dL decrease in Hb resulted in a -0.883 mL/min increase in the pLDF value (p < 0.001). Other factors, including age, sex, recipient site, and history of smoking or hypertension, diabetes, demonstrated no significant differences.

This study defined the quantitative relationship between systemic parameters and flap blood flow; specifically, 1 g/dL change in Hb is equivalent to 9 mmHg change in mBP in its effect on pLDF values. These findings provide a novel, objective formula for interpreting LDF data, allowing clinicians to distinguish systemic physiological changes from local vascular complications without relying solely on subjective experience.