Overview

   In surgical operation environments, anesthesia enables doctors to safe and accurate medical process with minimized movement and pain of patients. In general anesthesia, non-invasive and reliable monitoring of anesthesia depth is required because it is directly related with patient’s life. However, the current anesthesia depth monitoring approach, bispectral index (BIS), uses only electroencephalography (EEG) from the frontal lobe, and it shows critical limitations in the monitoring of anesthesia depth such as signal distortion due to electrocautery, EMG and dried gel, and false response to the special types of anesthetic drugs. In this paper, a multimodal head-patch system that simultaneously measures EEG and near-infrared spectroscopy (NIRS) on the frontal lobe is proposed. For EEG monitoring, mixed-mode DC-servo loop (MM-DSL) is proposed to cancel out the ±300mV electrode-dc offset (EDO) for dried gel condition with 3.59 noise-efficiency factor (NEF). To compensate the electro-magnetic noises (electromyograph, electrocautery) in the system level, NIRS signal is measured. Logarithmic transimpedance amplifier (logarithmic TIA) and closed-loop controlled (CLC) NIRS current driver are proposed. Logarithmic TIA can reject ambient light up to 10nA to achieve 60dB dynamic range. According to the comparator output, CLC NIRS driver duty-cycle can be adjusted from 0.625m to 50ms adaptively. The 16mm2 SoC is fabricated in 65nm CMOS. It dissipates 25.2mW peak power. With the combined signals, it can show the clinically important transition from the awake to deep state but BIS cannot detect the transition in a clinical trials.

Implementation results

Performance comparison

Architecture

Features

  - Mixed-mode DC-servo Loop

  - Logarithmic Transimpedance Amplifier

  - Closed-loop Controlled Current Driver

Related Papers

  - ISSCC 2017 [pdf]