An Improved Detrended Moving-Average Method for Monitoring the Depth of Anesthesia

The detrended moving-average (DMA) method is a new approach to quantify correlation properties in nonstationary signals with underlying trends. This paper monitored the depth of anesthesia (DoA) using modified DMA (MDMA) method. MDMA provides a power-law relation between the fluctuation function F_MDMA(s) and the scale s: F_MDMA( s)αs^α, where α is the slope of F_MDMA( s) in the logarithm scale. We applied the MDMA to monitor the DoA by computing the scaling exponent Fα and F_min values. To validate the proposed method, we compared our results with the bispectral index (BIS) monitor. We found a close correlation between our results and BIS with r( F_min) = 0.9346, r²(F_min) = 0.9183, and r(F_α) = 0.9458, r² (F_α) = 0.8855. Our method reflects the state of consciousness of a patient undergoing general anesthesia faster than BIS as observed clinically. The minimum time delay between the BIS and F_min trends was 12 s and the maximum was 178 s. Furthermore, in the case of poor signal quality, our results agreed with clinical observation, which indicates that our method can accurately estimate a patient´s hypnotic state in such circumstances. Fα and F_min trends are responsive and their movement seems similar to changes in the clinical state of the patients.