Development of a Microcontroller-based Measurement System for the Neuromuscular Blockade during Anesthesia

In medical surgery, anesthesiologists must keep track of a wide range of cardiac and respiratory parameters in addition to clinical indicators of ongoing anesthesia. For optimum surgical conditions, it is necessary to monitor neuromuscular blockades using diagnostic tools such as electromyograph (EMG), acceleromyograph (AMG), and mechanomyograph (MMG). Recently, short-acting drugs have become integral parts of modern anesthesia practice, which requires a real-time approach for measuring neuromuscular blockades, administering drugs, and controlling anesthesia. To achieve this goal, we have developed a microcontroller-based measurement system using an embedded Ethernet device called Ethernut containing an AVR-family microcontroller (ATmega128) and an Ethernet controller (LAN91C111). In this project, we have designed and built a new circuit board containing analog-to-digital converter (ADC) devices (MAX1270), which are connected to the expansion port of the Ethernut board. Our aim is to transmit ADC data via a local web server established on the Ethernut device using HTTP and TCP protocols with the help of an Ethernet controller. Our ADC board was designed and built using two 12-bit, 8-channel ADC MAX1270 devices, as well as op-amp buffers, digital isolators, an isolated DC/DC converter, and voltage regulators. The embedded Ethernet device, along with our ADC unit, provide us with a novel microcontroller-based measurement system. The main objective of the Ethernut-based data acquisition (DAQ) system is to retrieve data on neuromuscular blockades measured by various sensors (EMG, AMG, and MMG) from the MAX1270 integrated circuits (ICs) through the serial peripheral interface (SPI) port of the AVR microcontroller ATmega128. For our MAX1270-based ADC system, we developed a device driver program for working on Ethernut's real-time operating system Nut/OS, so it can in real time communicate with the ATmega128 microcontroller on the Ethernut board through the SPI port. We modified and tailored the HTTP server application of Nut/OS provided by egnite GmbH in order to establish a local HTTP/TCP server with the ADC device registered as a common gateway interface (CGI) on the Ethernut device for real-time data transmission over the Ethernet network to a desktop computer. We have programmed Ethernut's microcontroller to sample acquired data at 3 kHz and transmit it to its Ethernet-based real-time server in a standard format for data streams. A program like MATLAB on a desktop computer can retrieve and analyze the neuromuscular blockade data from this local server in order to monitor the status of a patient under anesthesia. The embedded DAQ system processes data from the neuromuscular sensors (EMG, AMG, and MMG) in a reliable way with a maximum bandwidth of about 400 Hz. Our results indicate that it can handle up to 1 kHz of data bandwidth. For higher data rates, the embedded device requires more memory space than is currently available. Therefore, this system is appropriate for processing sensor data with a moderate bandwidth. If we extend and improve our embedded Ethernet measurement system, it can be used for a number of practical applications in anesthesia clinics that require accurate observations of patient behavior. This microcontroller-based system is easily extensible and can be used as a controller for other automation applications.