# Estimating the Depth of Anesthesia from EEG Signals Based on a Deep Residual Shrinkage Network

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## Abstract

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## 1. Introduction

^{®}Brain Function Monitoring (Masimo, Irvine, CA, USA) device has been recently introduced, and its crucial parameter is the patient state index (PSI) [12]. Previous work shows that the agreement between the PSI and BIS is relatively good, and the SedLine monitor is advantageous because it has more channels than the BIS monitor [13].

## 2. Materials and Methods

#### 2.1. Dataset

^{®}Brain Function Monitoring (Masimo, Irvine, CA, USA) device, which was recently introduced into clinical practice and displays PSI as the index of sedation depth. The SedLine EEG sensor consists of 6 electrodes: 1 reference channel (CT), 1 ground channel (CB), and 4 active EEG channels (L1, L2, R1, and R2) placed in the frontal pole. During the midazolam anesthesia, the raw EEG signals are sampled at 178.2 Hz. The dataset we used records 4 channels’ raw EEG signals, PSI values, spectral edge frequency (SEF), burst suppression ratio, electromyographic (EMG) activity, and artifact percentage.

#### 2.2. EEG Signals Preprocessing

#### 2.3. Evaluation Metrics

#### 2.4. Deep Learning Model

#### 2.4.1. Deep Residual Shrinkage Network

#### 2.4.2. 1 × 1 Convolution

#### 2.4.3. Proposed Regression Model

#### 2.5. Conventional Models

#### 2.5.1. Features Extraction

- Band Power

- Spectral Edge Frequency

- Sample Entropy

#### 2.5.2. Conventional Regression Models

- Support Vector Machine

- Random Forest

- Artificial Neural Network

## 3. Results

#### 3.1. Experimental Settings

#### 3.2. Experimental Results

## 4. Discussion

- The recorded raw EEG signals are usually contaminated by electrical noise and other physiological signals. We used bandpass finite filters to remove electrical noise, and the WT-CEEMDAN-ICA algorithm to extract clean EEG signals.
- We adopted deep learning models to extract discriminative features automatically instead of extracting features manually from EEG signals.
- To improve our proposed model’s generalization ability and convergence speed, we standardized the EEG signals.
- DRSN-CW can deal with signals disturbed by noise, which is suitable for EEG-signal processing.

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**The algorithm flowchart of the WT-CEEMDAN-ICA method used to remove EOAs from EEG signals.

**Figure 3.**The structure of residual building block (RBB): (

**a**) the identity block where the input feature map is the same size as the output feature map. H, W, and C represent the height, width, and channels of the input and output feature map, respectively. (

**b**) the convolutional block where the size of the input feature map is different from that of the output feature map. There is a convolution operation and a Batch-normalization operation in the convolutional shortcut for changing the shape of the input. ${\mathrm{H}}_{1}$, ${\mathrm{W}}_{1}$, and ${\mathrm{C}}_{1}$ represent the height, width, and channels of the input feature map, respectively. ${\mathrm{H}}_{2}$, ${\mathrm{W}}_{2}$, and ${\mathrm{C}}_{2}$ represent the height, width, and channels of the output feature map, respectively. An RBB consists of two convolutional layers, two batch normalization (BN) layers, two rectifier linear units (ReLUs) layers, and one shortcut connection.

**Figure 4.**The structure of residual shrinkage building unit with channel-wise thresholds (RSBU-CW). ${\mathrm{H}}_{1}$, ${\mathrm{W}}_{1}$, and ${\mathrm{C}}_{1}$ represent the height, width, and channels of the input feature map, respectively. ${\mathrm{H}}_{2}$, ${\mathrm{W}}_{2}$, and ${\mathrm{C}}_{2}$ represent the height, width, and channels of the output feature map, respectively. There is a soft thresholding module in RSBU-CW. ${x}_{avg}$, z, and α are the indicators of the feature maps used to determine the threshold τ. x and y are the input and output feature maps of the soft thresholding module, respectively.

**Figure 5.**The illustration of 1 × 1 convolution. H, W, and C represent the height, width, and channels of the input feature map, respectively. A 1 × 1 convolution does not change the height or width but the number of channels of inputs.

**Figure 6.**The structure of our proposed model consists of the DRSN-CW block and 1 × 1 convolution block. The inputs of our proposed model are 4 channel-EEG signals, and the outputs are the corresponding predicted PSI values.

**Figure 8.**The classification performances (ACC, SE, and F1) of all the models on different anesthetized states (AW, LA, NA, and DA) and the regression performance (MSE) of all the models.

**Figure 9.**Part of the predicted PSI values of our proposed model. The red line represents the ideal prediction model where the predicted PSI values equal the ground truth PSI values exactly.

**Figure 10.**The regression and classification performances of the two models in the ablation experiment on the soft thresholding module in the RSBU-CW.

**Figure 11.**The classification performances (ACC, SE, and F1) of all the models on different anesthetized states (AW, LA, NA, and DA) and the regression performance (MSE) of all the models in cross-subject validation.

Metric | Formula | Description |
---|---|---|

MSE (Regression) | $\frac{1}{N}\times {\displaystyle \sum _{1}^{N}}{\left(\widehat{PSI}-PSI\right)}^{2}$ | Mean Squared Error |

ACC (Classification) | $\frac{TP+TN}{TP+FP+FN+TN}$ | Accuracy |

SE (Classification) | $\frac{TP}{TP+FN}$ | Sensitivity |

PR (Not used directly in this paper) | $\frac{TP}{TP+FP}$ | Precision |

F1 (Classification) | $2\times \frac{SE\times PR}{SE+PR}$ | F1-score |

**Table 2.**The regression and classification results (mean ± STD) of our proposed model and three conventional models. The mean squared error (MSE) result is the average of the five-fold cross-validation where we split all the samples into five groups, four groups are used as the train set, and one group is used as the test set for each cross-validation. The accuracy (ACC), sensitivity (SE), and F1-score (F1) results are the macro-averaging (we compute the metrics independently for each anesthetized state and then take the average) results of the 4 different anesthetized states.

Metrics | SVR | RF | ANN | Our Proposed Model |
---|---|---|---|---|

MSE | 166.02 ± 7.77 | 90.95 ± 4.88 | 109.20 ± 5.80 | 40.35 ± 3.22 |

ACC | 0.8596 ± 0.0574 | 0.8640 ± 0.0720 | 0.8606 ± 0.0380 | 0.9503 ± 0.0224 |

SE | 0.4825 ± 0.3391 | 0.6685 ± 0.1266 | 0.5650 ± 0.2801 | 0.8411 ± 0.0790 |

F1 | 0.475 ± 0.2941 | 0.6770 ± 0.0840 | 0.5901 ± 0.2337 | 0.8395 ± 0.0812 |

**Table 3.**The regression and classification results (mean ± STD) of our proposed model and three conventional models in cross-subject validation.

Metrics | SVR | RF | ANN | Our Proposed Model |
---|---|---|---|---|

MSE | 173.22 ± 8.56 | 97.56 ± 6.88 | 133.49 ± 5.40 | 49.22 ± 4.62 |

ACC | 0.7908 ± 0.1187 | 0.8420 ± 0.0765 | 0.8216 ± 0947 | 0.9203 ± 0.0470 |

SE | 0.4675 ± 0.3391 | 0.6575 ± 0.1266 | 0.5700 ± 0.1414 | 0.8054 ± 0.0243 |

F1 | 0.4599 ± 0.2132 | 0.6670 ± 0.0821 | 0.5852 ± 0.1274 | 0.8070 ± 0.0306 |

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## Share and Cite

**MDPI and ACS Style**

Shi, M.; Huang, Z.; Xiao, G.; Xu, B.; Ren, Q.; Zhao, H.
Estimating the Depth of Anesthesia from EEG Signals Based on a Deep Residual Shrinkage Network. *Sensors* **2023**, *23*, 1008.
https://doi.org/10.3390/s23021008

**AMA Style**

Shi M, Huang Z, Xiao G, Xu B, Ren Q, Zhao H.
Estimating the Depth of Anesthesia from EEG Signals Based on a Deep Residual Shrinkage Network. *Sensors*. 2023; 23(2):1008.
https://doi.org/10.3390/s23021008

**Chicago/Turabian Style**

Shi, Meng, Ziyu Huang, Guowen Xiao, Bowen Xu, Quansheng Ren, and Hong Zhao.
2023. "Estimating the Depth of Anesthesia from EEG Signals Based on a Deep Residual Shrinkage Network" *Sensors* 23, no. 2: 1008.
https://doi.org/10.3390/s23021008