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 F(α) 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, r(2)(F(min)) = 0.9183, and r(F(α)) = 0.9458, r(2)(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. F(α) and F(min) trends are responsive and their movement seems similar to changes in the clinical state of the patients.