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Automatic Control of General Anesthesia: New Developments and Clinical Experiments
Full text linkL’anestesia generale è uno stato di coma farmacologicamente indotto, temporaneo e reversibile. Il suo obiettivo consiste nel provocare la perdita totale della coscienza e nel sopprimere la percezione del dolore. Essa costituisce un aspetto fondamentale per la medicina moderna in quanto consente di praticare interventi chirurgici invasivi senza causare ansia e dolore al paziente. Nella pratica clinica dell’anestesia totalmente endovenosa questi effetti vengono generalmente ottenuti mediante la somministrazione simultanea del farmaco ipnotico propofol e del farmaco analgesico remifentanil. Il dosaggio di questi farmaci viene gestito dal medico anestesista basandosi su linee guida farmacologiche e monitorando la risposta clinica del paziente. Recenti sviluppi nelle tecniche di elaborazione dei segnali fisiologici hanno consentito di ottenere degli indicatori quantitativi dello stato anestetico del paziente. Tali indicatori possono essere utilizzati come segnali di retroazione per sistemi di controllo automatico dell'anestesia. Lo sviluppo di questi sistemi ha come obiettivo quello di fornire uno strumento di supporto per l'anestesista.
Il lavoro presentato in questa tesi è stato svolto nell'ambito del progetto di ricerca riguardante il controllo automatico dell'anestesia attivo presso l'Università degli Studi di Brescia. Esso è denominato ACTIVA (Automatic Control of Total IntraVenous Anesthesia) ed è il risultato della collaborazione tra il Gruppo di Ricerca sui Sistemi di Controllo dell’Università degli Studi di Brescia e l’Unità Operativa Anestesia e Rianimazione 2 degli Spedali Civili di Brescia. L’obiettivo del progetto ACTIVA consiste nello sviluppo teorico, nell’implementazione e nella validazione clinica di strategie di controllo innovative per il controllo automatico dell’anestesia totalmente endovenosa. Nel dettaglio, in questa tesi vengono inizialmente presentati i risultati sperimentali ottenuti con strutture di controllo basate sull'algoritmo PID e PID ad eventi per la somministrazione di propofol e remifentanil. Viene poi presentato lo sviluppo teorico e la validazione clinica di strutture di controllo predittivo basate su modello. Successivamente vengono presentati i risultati di uno studio in simulazione riguardante una soluzione di controllo innovativa che consente all'anestesista di regolare esplicitamente il bilanciamento tra propofol e remifentanil. Infine, vengono presentati gli sviluppi teorici ed i relativi studi in simulazione riguardanti soluzioni di controllo personalizzate per le fasi di induzione e mantenimento dell'anestesia.General anesthesia is a state of pharmacologically induced, temporary and reversible coma. Its goal is to cause total loss of consciousness and suppress the perception of pain. It constitutes a fundamental aspect of modern medicine as it allows invasive surgical procedures to be performed without causing anxiety and pain to the patient. In the clinical practice of total intravenous anesthesia, these effects are generally obtained by the simultaneous administration of the hypnotic drug propofol and of the analgesic drug remifentanil. The dosing of these drugs is managed by the anesthesiologist on the basis of pharmacological guidelines and by monitoring the patient's clinical response. Recent developments in physiological signal processing techniques have introduced the possibility to obtain quantitative indicators of the patient's anesthetic state. These indicators can be used as feedback signals for automatic anesthesia control systems. The development of these systems aims to provide a support tool for the anesthesiologist.
The work presented in this thesis has been carried out in the framework of the research project concerning the automatic control anesthesia at the University of Brescia. The project is called ACTIVA (Automatic Control of Total IntraVenous Anesthesia) and is the result of the collaboration between the Research Group on Control Systems of the University of Brescia and the Anesthesia and Intensive Care Unit 2 of the Spedali Civili di Brescia. The objective of the ACTIVA project consists in the theoretical development, implementation, and clinical validation of innovative control strategies for the automatic control of total intravenous anesthesia. In detail, in this thesis the experimental results obtained with control structures based on the PID and on event-based PID controllers for the administration of propofol and remifentanil are initially presented. The theoretical development and clinical validation of model predictive control strategies is then proposed. Next, the results of a simulation study regarding an innovative control solution that allows the anesthesiologist to explicitly adjust the balance between propofol and remifentanil are given. Finally, the theoretical developments and the relative simulation studies concerning personalized control solutions for induction and maintenance phases of anesthesia are explained
Tuning of a predictive control scheme for intravenous anesthesia: influence on performance and computational requirements
No full textThis paper focuses on a Model Predictive Control (MPC) application for the multivariable control of depth of hypnosis in total intravenous anesthesia. The control system co-administers propofol and remifentanil to regulate the Bispectral Index (BIS). A key feature of the clinical practice is the setting of a ratio between the two drugs, which defines the opioid-hypnotic balance. This ratio must be explicitly controlled by the anesthesiologist to implement a balanced anesthesia technique. However, since propofol and remifentanil have a synergistic effect when they are co-administered, the response of the patient to drug administration changes according to the selected value of the ratio. Consequently, the MPC parameters must be carefully tuned for each specific ratio to ensure performance and robustness. This tuning is typically performed by means of optimization techniques, which are computationally demanding and require several hours to complete. This approach is feasible for a fixed, predefined ratio but becomes impractical when the ratio needs to be adjusted in real-time based on the clinical situation. To solve this problem, this paper proposes a methodology based on precomputed lookup tables and fitting techniques. This solution provides near-optimal tuning parameters for any ratio within a defined clinical range, eliminating the need for real-time optimization. The performance and robustness of the proposed method are evaluated through a simulation study, showing results that are consistent with clinical requirements. The proposed approach represents a step towards the deployment of flexible MPC-based control solutions in the clinical practice
Tuning of a Predictive Control Scheme for Intravenous Anaesthesia Exploring Set of Fixed Ratios
No full textThis work addresses automatic control of total intravenous anaesthesia performed by exploiting a Model Predictive Control (MPC) technique. The analyzed control scenario considers simultaneous infusion of propofol and remifentanil to attain hypnotic and analgesic effects, respectively. As common in the clinical practice, a fixed ratio between these infused drugs is assumed. Such a ratio can be set by the anaesthesiologists according to the type of medical intervention and to their individual preferences. Thus, it is necessary to account for this aspect of clinical practice during the control system design stage. This is obtained through the use of a suitable MPC-based control architecture whose tuning parameters are adequately computed by taking into account the selected ratio. The methodology provided in this work first addresses the tuning for a fixed set of ratios. Subsequently, a generalization of the approach is provided to allow any ratio belonging to a defined range. The effectiveness of the presented solution is evaluated through a simulation study
On the practical use of a PID-based control scheme for automatic control of general anesthesia
No full textDespite promising results have been obtained in clinical trials, closed-loop control systems for general anesthesia are not routinely used in the clinical practice yet. One of the possible reasons is that problems related to their practical implementation are not fully solved. In particular, a control system must be able to cope with manual interventions from the anesthesiologist and to operate with different devices commonly available in surgery rooms. In this paper we present experimental results where a PID-based control system has been tested when drug boluses are manually administered by the anesthesiologist and when different syringe pumps are used. The performance of the control system has been assessed on a group of nine patients undergoing elective plastic surgery. Results demonstrate that the control system is capable to handle these practical issues and it is therefore suitable to be used in the clinical practice
Analysis of the performance achievable with a PIDD2α controller for depth of hypnosis in total intravenous anesthesia
No full textIn this paper we use a population-based approach to design a fractional-order Proportional-Integral-Double-Derivative (PIDD2α) controller for Depth-of-Hypnosis (DoH) in general anesthesia. In particular, we consider the control problem of achieving and keeping the bispectral index (BIS) at the required value by manipulating the infusion rate of the propofol drug. The performance of the controller is then analyzed and compared with that achieved with a Proportional-Integral-Derivative (PID) and a Proportional-Integral-Derivative-Acceleration (PIDA) controller. Results show that, with the considered design methodology, the improvement obtained by using a fractional-order double-derivative action is marginal and does not justify the increment of the complexity in the controller implementation
Experimental Results of an Optimized PID Controller for General Anesthesia with Adjustable Opioid-Hypnotic Balance
No full textClosed-loop control of total intravenous anesthesia (TIVA) is an emerging technology expected to have a significant impact on clinical practice in the upcoming years. However, for these systems to become widely acceptable in clinical practice, they should not aim to replace the anesthesiologist; instead, they must act as tools capable of enhancing the abilities of the clinician. Thus, it is important to develop control structures that allow the human operator to adjust the behavior of the controller based on clinical considerations. In the clinical practice of TIVA, balanced anesthesia is a technique that involves properly dosing the administration of propofol and remifentanil to optimize the therapeutic effect of each drug while minimizing their individual side effects. The anesthesiologists perform this technique by regulating the ratio between the infusion rates of these two drugs, known as the opioid-hypnotic balance. In this paper, we present and discuss the experimental results obtained with a PID-based control architecture for propofol and remifentanil co-administration where such a controller has a tuning parameter that can be regulated by the anesthesiologist to achieve the desired opioid-hypnotic balance
MPC for Propofol Anesthesia: the Noise Issue
Full text linkThe design of automatic control systems for general anesthesia is a challenging task due to the severe safety requirements and process constraints. This is even more complex when model-based control techniques are used due to the significant variability of the process model. Additionally, issues like noisy measurements and interference also influence the control system overall performance. In this context, adequate filtering and control system sampling period selection should be analyzed to test their influence on the controller. In this paper, an MPC system for the depth of hypnosis, where the BIS signal is used as a controlled variable, is analyzed. The main purpose is to test and evaluate how the process noise affects the performance of the control system. The analysis is performed in a simulation study using a dataset of virtual patients representative of a wide population. Results show that a satisfactory performance is obtained when the noise is explicitly taken into account in the controller tuning procedure for a specific sampling period
Experimental Evaluation of Analgesia With an Event-Based PID Control Strategy for Anesthesia
Full text linkThe recent introduction of the Conox monitoring system in the clinical practice of total intravenous anesthesia (TIVA) has opened new research opportunities. Indeed, it provides the qCON and the qNOX indexes, which give a measure of hypnosis and analgesia, respectively. This letter presents the first experimental results of closed-loop anesthesia performed by using the Conox monitoring system. In particular, we exploited the qCON as the feedback variable for an event-based PID multiple-input single-output (MISO) controller and we recorded the qNOX to evaluate analgesia. Clinical experiments have been performed on four patients undergoing general anesthesia for elective plastic surgery. The controller demonstrated a satisfactory performance in maintaining qCON within the desired range for all patients. An optimal qNOX level has also been achieved in three out of four cases, while, in one patient, the qNOX level indicated a slight excess of analgesia. These findings suggest that the proposed MISO architecture is effective in providing adequate levels of hypnosis and analgesia and that, in future works, the qNOX information could be leveraged in the controller design to enhance analgesia control
Generalized Haalman tuning of PIDA controllers
Full text linkIn this paper we propose a new tuning methodology for Proportional-Integral-Derivative-Acceleration (PIDA) controllers. First, a third-order-plus-dead-time transfer function of the (high-order) process is estimated by evaluating an open-loop step response. Then, the three time constants of the controller are determined by applying a pole-zero cancellation approach and the proportional gain is finally adjusted in order to obtain a desired maximum sensitivity. The controller filters are selected in order to minimize the effects of the measurement noise and to avoid kicks in the control variable. Simulation results show the effectiveness of the methodology in comparison with PID control
PIDA control of depth of hypnosis in total intravenous anesthesia
Full text linkIn this paper we discuss the use of a Proportional-Integral-Derivative-Acceleration (PIDA) controller for the Depth-of-Hypnosis (DoH) control in total intravenous anesthesia (TIVA). In particular, the infusion rate of the hypnotic drug propofol is the control variable and the bispectral index (BIS) is the controlled variable. The PIDA controller is tuned by using a population-based approach and its robustness is evaluated with a Monte Carlo method. The noise amplification is reduced by means of suitably designed low-pass filters. A comparison with a PID controller is performed, showing that the addition of the acceleration action allows us to design a more aggressive controller, thus reducing the risk of awareness of the patient in the maintenance phase
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