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USABILITY EVALUATION OF A DUAL CLOSED-LOOP ANESTHESIA SYSTEM
Abstract
Introduction: iControl v3 is a system for closed-loop control of propofol and remifentanil anesthesia in adults. It includes a touch-screen user interface, the NeuroSENSE EEG monitor, two Alaris infusion devices and speakers for audible alarms. Previous versions of the system have been clinically evaluated [1]. The system has been designed for investigational use, with patient safety as a key priority. The aim of this study was to evaluate the system's usability in the hands of expert users. The purpose of this formative evaluation was to guide development of the user interface, verify appropriate configuration of devices and demonstrate that the system can provide a safe and acceptable interface for the clinical evaluation. Results of the study will further inform risk identification, formulation of Instructions for Use (IFU) and design of the training scheme [2]. Methods: Institutional review board approval and informed consent were obtained to conduct the evaluation with staff from the Department of Anesthesia. All participants were given an introduction to the system and were asked to 'think aloud' during the evaluation, while their comments were captured with a voice recorder [3]. After a brief opportunity to use the equipment without instruction, a structured evaluation was conducted, in which participants followed a specific set of verbal prompts for 18 safety-critical tasks and 12 administrative tasks. Each participant provided post-test verbal feedback and completed the Computer System Usability Questionnaire (CSUQ) [4], in which positive statements about the system were scored on a scale of 1 (strongly agree) to 7 (strongly disagree). Results: Usability was evaluated by 15 potential users (12 staff anesthesiologists, 2 residents and 1 anesthesia assistant), all reporting normal or corrected-to-normal vision. Twenty-three usability issues were observed and/or reported by participants. These related to confirmation of data input (n=6), understanding displayed information (n=4), use of the touch screen interface (n=3), identification and interpretation of error messages (n=3), operation of infusion devices (n=3), organisation of lists and graphical information (n=3) and the log-in/-out process (n=1). These issues suggested improvements to the IFU and/or focus points for training; 2 issues were resolved by modifying peripheral equipment and 4 issues prompted minor software changes to the user interface. Participants completed all evaluation tasks: 17/18 safety-critical tasks and 9/12 administrative tasks were completed by more than 90% of participants without assistance; however, for one safety critical-task (identify an infusion rate), 23% of participants needed assistance. The CSUQ (median score 3, inter-quartile range 2-4) suggested the system met user expectations. Discussion: After only a brief informal introduction, representatives of the target user group were able to safely operate the system with minimal assistance. Solutions were provided for the identified usability issues and additional requirements were recorded for consideration in future releases. The system and IFU will be subjected to a summative evaluation prior to the start of clinical testing to verify that identified solutions are effective.
... Before starting the study, the system was extensively tested in the laboratory for reliability, repeatability, and usability 31 and was approved by Providence Health Care's Lower Mainland Biomedical Department for use in the Royal Columbian Hospital operating rooms. ...
... The system included an informative and intuitive user interface, which presented infusion profiles, calculated C e values, WAV CNS , and BSR graphically, and was subjected to numerous rounds of preclinical testing. 31 Detailed information on perceptions or use of the system features was not collected during this study. One anesthesiologist conducted the majority of cases during both phases. ...
Background:
Closed-loop control of anesthesia involves continual adjustment of drug infusion rates according to measured clinical effect. The NeuroSENSE monitor provides an electroencephalographic measure of depth of hypnosis (wavelet-based anesthetic value for central nervous system monitoring [WAVCNS]). It has previously been used as feedback for closed-loop control of propofol, in a system designed using robust control engineering principles, which implements features specifically designed to ensure patient safety. Closed-loop control of a second drug, remifentanil, may be added to improve WAVCNS stability in the presence of variable surgical stimulation. The objective of this study was to design and evaluate the feasibility of a closed-loop system for robust control of propofol and remifentanil infusions using WAVCNS feedback, with an infusion safety system based on the known pharmacological characteristics of these 2 drugs.
Methods:
With Health Canada authorization, research ethics board approval, and informed consent, American Society of Anesthesiologists I-III adults, requiring general anesthesia for elective surgery, were enrolled in a 2-phase study. In both phases, infusion of propofol was controlled in closed loop during induction and maintenance of anesthesia, using WAVCNS feedback, but bounded by upper- and lower-estimated effect-site concentration limits. In phase I, remifentanil was administered using an adjustable target-controlled infusion and a controller was designed based on the collected data. In phase II, remifentanil was automatically titrated to counteract rapid increases in WAVCNS.
Results:
Data were analyzed for 127 patients, of median (range) age 64 (22-86) years, undergoing surgical procedures lasting 105 (9-348) minutes, with 52 participating in phase I and 75 in phase II. The overall control performance indicator, global score, was a median (interquartile range) 18.3 (14.2-27.7) in phase I and 14.6 (11.6-20.7) in phase II (median difference, -3.25; 95% confidence interval, -6.35 to -0.52). The WAVCNS was within ±10 of the setpoint for 84.3% (76.6-90.6) of the maintenance of anesthesia in phase I and 88.2% (83.1-93.4) in phase II (median difference, 3.7; 95% confidence interval, 0.1-6.9). The lower propofol safety bound was activated during 30 of 52 (58%) cases in phase I and 51 of 75 (68%) cases in phase II.
Conclusions:
Adding closed-loop control of remifentanil improved overall controller performance. This controller design offers a robust method to optimize the control of 2 drugs using a single sensor. The infusion safety system is an important component of a robust automated anesthesia system, but further research is required to determine the optimal constraints for these safe conditions.
... In order to reduce the risk of user errors, the iControl system has undergone formal usability evaluations [22] comprised of think-aloud task completion [23] and the standard Computer System Usability Questionnaire (CSUQ) [24]. The purpose of these evaluations was to improve the usability of the system in the hands of expert users. ...
Many aspects of modern medicine, including the administration of anesthetic agents during general surgery, remain unautomated and reliant on the vigilance of the attending clinicians. In other fields where failures can have catastrophic consequences, such as the aviation and nuclear power industry, automated control regimens have been adopted to reduce the risks and improve performance.
In this paper we discuss many aspects of the implementation of a complete automated system for intravenous anesthetic drug infusion based on feedback from electroencephalography (EEG) readings. The system software in its entirety consists of approximately 22K lines of Scheme code and features a client-server implementation interfacing medical devices with a portable graphical user interface. The user interface runs on both mobile devices and dedicated medical flat panel displays.
The strengths of the Scheme functional language have been leveraged to build a robust maintainable modular system with extensive testing facilities to mitigate the inherent safety hazards associated with the application.
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