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AUTOMATED ANAESTHESIA |
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CONTROL TECHNIQUES IN ANAESTHESIA |
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The main goals of clinical anaesthesia are the maintenance of drug induced unconsciousness, muscle relaxation and analgesia. Although intra-operative analgesia is an integral part of general anaesthesia, its role for post-operative pain relief is indispensible. |
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Intra-operative unconsciousness and muscle relaxation can be achieved by automatic control while post-operative patient- controlled analgesia (PCA) is a sort of manual control. |
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Control of Unconsciousness: |
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One of the main tasks of the anesthetist during surgery is to control anaesthetic depth. At the ether era, anaesthetic depth was defined by Guedel classification. Nowadays, anaesthetic depth shows good correlation with EEG, BP, HR, endtidal concentrations of anaesthetic agents, oesophageal motor activity or somatosensory or auditory evoked potentials. However, BP proved to be the most reliable guide for assessing anaesthetic depth and dosing inhaled vapours. The mean reason for automating the control of anaesthetic depth is to release the anaesthetist so that s/he can devote attention to other tasks as controlling fluid balance, ventilation and drug application which cannot yet be adequately automated, thus increasing the patient safety. |
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Computer controlled drug administration: |
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Drug administration by computer can be designed as either closed loop or open loop systems. |
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Closed Loop Anaesthesia: |
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A controller is designed and implemented on a personal computer. The controller makes use of an error between desired and actual values of BP, through negative feedback control. Correcting this error can be achieved by an inhalation anaesthetic as isoflurane delivered by an electronic vaporizer, or by iv agent as propofol or alfentanyl delivered by a computerized infusion pump. The anaesthetist supervising the controller does not interfere in the system and all workers have proved supreme haemo-dynamic stability with closed loop system exceeding the findings when BP is manually controlled during general anaesthesia. |
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Open Loop Anaesthesia: |
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It has no input signal but it uses mathematical models and equations to produce predicted drug concentration in the blood. With this system the anaesthetist selects the blood concentration considered appropriate for the individual patient and the pharmacokinetic model is used to calculate the infusion rate required to achieve this target concentration. A target controlled infusion model calculates the distribution and elimination of the drug and the infusion rates necessary to achieve and maintain a target blood concentration. The infusion rates are transmitted to a pump which then delivers the drug iv to the patient. |
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Patient Controlled Aanalgesia (PCA): |
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PCA can be considered a type of closed infusion system where the patient provides the input signal to control the administration of the analgesic drug. He is considered an integral part of the closed system as the actual versus desired values of pain relief. This has proved to be an effective technique for treating postoperative pain. |
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Control of muscle relaxation: |
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The degree of neuromuscular block is usually monitored by observing the muscle response to nerve stimulation, commonly the ulnar nerve. Bolus doses of neuromuscular blocker are usually administered intermittently based on this response. However, this method inevitably leads to fluctuations in the degree of neuromuscular block, particularly with recently introduced short-acting agents. To reduce this effect, continuous infusion of neuromuscular blocker may be used, but differences in pharmacodynamics and pharmacokinetics between patients make it difficult to choose the correct infusion rate to maintain the desired level of neuromuscular block. Closed-loop control offers the ability to provide a stable level of neuromuscular block allowing for variations in individual responses to neuromuscular blocking agents. |
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Early work on feedback control of drug infusion for muscle relaxation was carried out experimentaly on sheep, followed by successful human clinical trials A Datex relaxograph, a mathematical model, a syringe driver and the patient are the components of a closed loop control which offers the ability to provide a stable level of neuro-muscular block allowing for variations in individual response to neuro-muscular blocking agents. | |
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Starting by a loading relaxant dose, a controlled relaxant rate is infused in the patient through this closed system to be stopped before the end of surgery and reversing the relaxant effect. |
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Advanced controllers:
Recently, multivareable anaesthesia has been possible by using more than one controller in the system. Again, an optimum controller uses a comparator for directing one controller or the other to the best correction of the error between input and output. |
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The major problem of feedback control in anaesthesia is that there are enormous patient to patient variations in dynamic model parameters. Thus, it is difficult to design a fixed controller suitable for all patients. This led to the investigation of self-adaptive and self-organizing control strategies for intelligent control of mechanical ventilation, anaesthetic depth, muscle relaxation and other parameters.
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Through the early decades of the coming century, control strategies will expand the concept of automation. However, an advance in microprocessor technology has started to bring automation to all levels of application. Intelligent control systems with the ability of decision-making will gradually take larger shares in automatic control of anaesthesia and intensive care.
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System Automatically Delivers Anesthesia Medications During Surgery
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A team of French anesthesiologists has developed an automatic delivery system of propofol and remifentanil, which they recently tested in a multi-center trial involving 196 surgical patients. The researchers reported in Anesthesia & Analgesia that the system, which uses a Bispectral Index (BIS) monitor as a guide, performed better than manual administration.
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The controller allows the automated delivery of propofol and remifentanil and maintains BIS values in predetermined boundaries during general anesthesia better than manual administration.
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Closed-Loop Coadministration of Propofol and Remifentanil
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McSleepy: Automated Anesthesia System
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Canadian Researchers at McGill University in Montreal, Quebec and the McGill University Health Centre (MUHC) have developed an automated anesthetic system and believe they were the first in the world to perform a surgery with such a machine. The new system, named ‘McSleepy’.
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The anesthetic technique was used on a patient who underwent a partial nephrectomy, a procedure that removes a kidney tumor while leaving the non-cancerous part of the kidney intact, over a period of three hours and 30 minutes.
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To manipulate the various components of general anesthesia, the automated system measures three separate parameters displayed on a new Integrated monitor of anesthesia (IMATM): depth of hypnosis via EEG analysis, pain via a new pain score, called AnalgoscoreTM, and muscle relaxation via phonomyographyTM, all developed by ITAG. The system then administers the appropriate drugs using conventional infusion pumps, controlled by a laptop computer on which “McSleepy” is installed.
Using these three separate parameters and complex algorithms, the automated system calculates faster and more precisely than a human can the appropriate drug doses for any given moment of anesthesia. | |
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“McSleepy” assists the anesthesiologist in the same way an automatic transmission assists people when driving. As such, anesthesiologists can focus more on other aspects of direct patient care. An additional feature is that the system can communicate with personal digital assistants (PDAs), making distant monitoring and anesthetic control possible. In addition, this technology can be easily incorporated into modern medical teaching programs such as simulation centers and web-based learning platforms. |
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Ref: |
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1. CONTROL TECHNIQUES IN ANAESTHESIA; BY Prof. M. EZZAT MOEMEN, founder of the department of anaesthesia. |
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2.Faculty of medicine, Zagazig universityClosed-loop anaesthesia delivery system (CLADS) using bispectral index: a performance assessment study. Anaesth Intensive Care. 2007 Jun;35(3):357-62. |
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3. Evaluation of a novel closed-loop total intravenous anaesthesia drug delivery system: a randomized controlled trial. Br. J. Anaesth. (2013) |
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4. Abstract in Anesthesia & Analgesia: Closed-Loop Coadministration of Propofol and Remifentanil Guided by Bispectral Index: A Randomized Multicenter Study. |