Abstract Background and Aims Chronic kidney disease is a growing problem worldwide with a growing number of patients requiring kidney replacement therapy. In recent years we have developed a novel device for peritoneal dialysis (PD), the WEarable Artificial KIDney (WEAKID); composed of a wearable device connected to a dialysate reservoir. WEAKID uses both sorbent technology and continuous flow PD to improve dialysis efficacy. Formative usability testing aids to the identification of design issues that may interfere with a device's safe and effective use and thus may influence decisions made in the design process. Here, we present the results of an international, multicentre, formative usability study of WEAKID among nurses and patients. Method This study used a mixed-methods design and was conducted in hospitals in Italy (Modena University Hospital), Spain (La Paz University Hospital, Madrid), and the Netherlands (University Medical Center Utrecht) between November 2021 and December 2022. An individual, formative usability testing session was conducted with each participant (nurse or patient) under the conditions of simulated use. Participants were asked to perform basic operational procedures (i.e. turning the device on/off, input of dialysis settings, handling an alarm) with the device according to a usability task list. Their performance was observed and use errors (i.e., something that a participant does or fails to do that results in an unexpected or unintended outcome) were noted. Furthermore, participants were asked for feedback, both verbally and by means of completing the system usability scale (SUS), reflecting perceived usability on a scale from 0 (worst) to 100 (best). Results We included 14 participants (n = 6 nurses, n = 8 patients) in three participating centres. All nurses were female and had a median experience with PD of 20.5 years (range 0.5-32). Patients were generally highly educated (n = 5, 63%). In total, 22 use errors occurred, 10 in nurses and 12 in patients. These use errors included factors not related to the device, e.g. not taking appropriate hygiene measures. In particular, use errors occurred during the priming/connection of catheter and handling the alarm. Participants’ feedback mainly concerned the small screen (and thus font) size, user interface (e.g. lack of colour-coded soft buttons), and (short) length of the patient line. The mean SUS score was 70 (range 57.5–85) for nurses, and 71.9 (range 55–87.5) for patients. Conclusion Despite the slightly above-average perceived usability of the device's current design stage, participants made a lot of suggestions for improvements, and usability must be improved to make the device ready for market introduction.
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