Abstract
BACKGROUND:
Early mobilization is important to improve critically ill patients’ outcomes, but barriers to its implementation are common. A suitable in-bed device to exercise patients’ legs might facilitate early mobilization.
OBJECTIVE:
The aim of this study was to develop an in-bed leg press that would facilitate early mobilization and enhance strength training of patients in acute care settings.
METHODS:
A user-centered design approach was applied to develop the device. The process was assessed by different instruments: the system usability scale (SUS) questionnaire, the Kano model questionnaire and interviews with end-users.
RESULTS:
Through several iterations of a user-centered design process, the prototype of an in-bed leg press was developed and tested. The assessment, based on SUS, Kano and interviews, indicates high usability and demonstrates the advantages of a user-centered design process.
CONCLUSIONS:
An interprofessional user-centered design approach was successfully implemented to develop a medical device. The early involvement of end-users resulted in a design that already shows a high degree of production readiness. The resulting device fulfilled all core requirements from a therapeutic point of view and included key features related to its practical use.
Introduction
Early mobilization is recommended in critically ill adults to counter physical or psychological complications [1]. However, there are many barriers that limit early implementation in acute care settings, for example, lack of staff or equipment [2]. These barriers prolong immobility unnecessarily, which is associated with muscle weakness and short-term functional disability [3]. Following a critical illness, patients are often too weak to stand on their legs and risk further injury from falls [4]. Commonly, intensive functional rehabilitation and early mobilization start as soon as cardiorespiratory stability has been achieved using a stepwise progression from manually assisted in-bed exercises to out-of-bed mobility training, such as sitting on the edge of the bed [5]. While endurance training can be facilitated with in-bed cycling ergometers [6], a market analysis indicated that an in-bed device for easy implementation of resistance training of the lower extremities is currently lacking. There are, for example, complex devices for mobilization or neurorehabilitation that require the patient to be moved out of bed into the device, and there are leg presses for sports exercises, but there was no medical in-bed leg exercise device commercially available. Clinical staff confirmed this lack of such a device to further optimize early mobilization.
An in-bed leg press device that is suitable to exercise critically ill patients must fulfil various requirements. First, the device should allow safe implementation in the acute care setting, such as an intensive care unit (ICU) or a step-down unit. This means the device must not interfere with other medical equipment and it should be certified as a medical device. Second, physiological movement for optimal and potentially assisted strength training should be supported. Third, the device must be usable in bed so that training may start as early as possible, i.e. devices that require the patient to be moved out of bed were not deemed acceptable. Fourth, the device must adhere to infection control standards. Finally, an in-bed leg press should be easily transported and installed to enhance applicability in practice.
Often it seems that the development of a medical device is initiated by results from fundamental research usually conducted in a laboratory setting. The design starts with new insights from research and tries to translate those into clinical practice. This inherits the risk that the final design will not meet the needs of end-users, e.g. the clinical staff. In contrast, involvement of end-users in the development phase encourages a strong focus on the usability and acceptability of the device [7]. Implementing a user-centered design (UCD) approach has the potential to achieve high usability and acceptability by involving the future users right from the beginning [8, 9].
The aim of this study was to develop an in-bed leg-press device to facilitate strength training. The device must be suitable for early mobilization in acute care settings given that the need for such a device was put forward by ICU staff. The focus was set on the implementation of an interprofessional, user-centered design process. It was the intention to demonstrate that early involvement of end-users is beneficial.
Methods
The need for a new device to facilitate early mobilization of the lower extremities was recognized by physiotherapists and nurses in the acute care setting. Therefore, a user-centered design approach was chosen to develop a new in-bed leg press. A mixed-methods approach was used, combining quantitative and qualitative measurement instruments to evaluate the process and to analyze the resulting strengths and weaknesses.
User-centered design approach
A user-centered design (UCD) approach refers to a process of designing a device from an end-user perspective whereby end-users are actively involved from the beginning of the process. According to ISO 9241-210:2019 [10], the UCD process consists of three main stages that are repeated until a solution is achieved, with all steps involving the participation of the end-users:
step 1: specification of user requirements; step 2: development of corresponding solutions; step 3: evaluation of the solutions with respect to the defined requirements.
In this study, the UCD was performed in two iterations or phases. In phase 1, brainstorming sessions were conducted involving health care professionals (physiotherapists, nurses), researchers and (biomedical) engineers to specify and prioritize the user requirements (step 1). Following these sessions, different technical solutions were analyzed and eventually a functional model was developed (step 2). This model was assessed by the end-users in hands-on tests (without patients) and discussions (step 3).
In phase 2, the three steps were repeated in order to design a prototype that was fit for use in a clinical environment. A more advanced usability test that consisted of two parts was introduced in this iteration (step 3). All participating physiotherapists were instructed in person for 30 minutes on how to use the prototype. In addition, a pocket card with instructions was available with the leg press. In the first part, physiotherapists used the device in their clinical practice for approx. four weeks on the ICU or step-down unit. The device was used with patients who were deemed suitable by the physiotherapists; since the usability of the device was of primary interest, the physiotherapists were free to include any patient that they assumed could benefit from using the device as part of the early mobilization scheme. There were no specific inclusion criteria with respect to the diagnosis of the patients. Subsequently, their experiences were evaluated using standardized assessment tools. For the second part, the prototype was improved based on the physiotherapists’ feedback and an updated version was tested for a further four weeks by a second, distinct group of acute care physiotherapists. As before, in this test the physiotherapists decided which patients would use the device. These tests were again followed by an evaluation process using the same standardized tools to determine usability, desirability and feasibility. In summary, the UCD process consisted of different phases and iterations such that user feedback was integrated thoroughly. Testing the device with acute care patients was part of this process. Figure 1 summarizes the UCD approach implemented in this study.
The user-centered design (UCD) process implemented in this study.
The responsible ethics committee of the canton of Bern was approached and it ruled that the study did not fall under the Swiss Human Research Act (Req-2020-01353). The use of the prototype in the Department of Intensive Care Medicine was approved by the internal technical commission of the University Hospital Bern. The device was also assessed, approved and frequently checked by representatives of the Department of Infection Control.
Feedback after phase 1 was documented and used as input for the development of the prototype. The usability study performed in phase 2 was evaluated using the system usability scale (SUS) questionnaire, the Kano model and interviews. This publication focusses on the phase 2 usability assessment.
The SUS questionnaire is designed for measuring an application’s usability; it consists of ten questions related to the user-friendliness of a product [11, 12]. The German translation of the SUS was used. Each question is answered on a 5-step Likert scale (from disagree to fully agree). The final score is calculated from the sum of the single values (1–5) and multiplied by 2. Consequently, the SUS can result in a maximum score of 100, which is the best possible score. Applying the SUS at different stages of a development – here it was used to assess the prototype and its improved version – allows comparison between different designs. The two SUS measurements in this study were compared statistically. Data were checked for normal distribution using the Shapiro-Wilk test. A
The Kano model also utilizes a questionnaire to obtain a differentiated view of a product’s functionality and performance [13]. This Kano questionnaire must be created for each specific application. The model defines three dimensions that must be included in the questionnaire: (i) must-be requirements, (ii) one-dimensional requirements, and (iii) attractive requirements. The must-be requirements do not improve a product in the customer’s perception but lead to dissatisfaction if missing. The one-dimensional requirements increase customer satisfaction linearly. The attractive requirements relate to the excitement the product induces in the customer; it is because of such features that a customer decides to choose a product. A pair of questions is formulated for each feature and answer options use a 5-interval Likert scale (from like to dislike). In the pair of questions, the first question asks if the device has the certain feature (a functional form of a question) while the second question asks if the product does not have the feature (a dysfunctional form of the question) [14]. The results of the Kano model are presented as percentage of agreement to each question. Thus, it can be identified whether the users regard a certain feature as a must-be, a one-dimensional or an attractive requirement, respectively.
The questions used to structure the interviews
The questions used to structure the interviews
As a third measure, an interview was conducted with each physiotherapist who had tested the prototype or the improved prototype in phase 2 (Fig. 1): the interview (duration approx. 30 min.) explored the user experience. It was based on a self-developed interview guide (Table 1) and comprised 5 main questions (open-ended, as narrative prompt) and 7 follow-up questions [15]. During each interview, a mind map summary including the main topics was created and validated by the interviewee [16]. Finally, the mind maps were compiled into a single overview and a thematic analysis was performed to identify relevant topics.
Technical development
Bedside leg press. Functional model positioned in a hospital bed (phase 1, left), first prototype (phase 2, right).
Figure 2 illustrates the functional model (phase 1) and the first prototype (phase 2). In phase1 of the development, the key requirements of an in-bed leg press for patients in critical care were established and implemented into a functional model. Eventually, the functional model allowed for exercises with one or two legs in three different training modes: alternate pedaling, single leg pedaling and isometric training against the system’s resistance. The model makes use of a pneumatic system that enables regulation of resistance through valves. Such a mechanism also ensures a high level of patient safety as the device stops immediately if no force is applied. The device is a self-contained system and does not require electricity or air pressure connections. Furthermore, it is portable and lightweight such that one person can easily carry and position the device in bed.
After assessing the functional model, the physiotherapists concluded that the concept fulfils the relevant requirements for early mobilization of the legs. Consequently, in phase 2, a prototype was developed, i.e. the device was re-engineered to enable a test in a clinical setting. For example, the prototype’s pedals were changed to allow adjustment of the dorsiflexion angle in three different positions. A casing was added to cover moving parts as an aspect of safety, but also for reasons of hygiene as it must be possible to easily disinfect the surface of the prototype.
As part of phase 2, the prototype was used by physiotherapists and then improved further. Figure 3 summarizes the changes introduced after the first round of the practical tests. This improved prototype was then used in the second round of tests and concludes the technical development.
Improvements introduced to the prototype between the first and second rounds of the tests in the intensive and intermediate care units.
A total of 9 physiotherapists participated in the study and tested the in-bed leg press in the ICU and step-down unit of the Department of Intensive Care Medicine at the Inselspital, Bern University Hospital, Bern, Switzerland.
The scores of the system usability scale (SUS). The score increased after modifying the prototype (i.e. from Group 1 to Group 2, statistically not significant).
All participating physiotherapists filled in the SUS questionnaire. As shown in Fig. 4, the mean SUS score of Group 1 was 68/100. After modifying the leg press, the mean score increased to 73/100. Data were normally distributed (Shapiro-Wilk test,
The results of the Kano questionnaire are summarized in Table 2. As this questionnaire aims to categorize the different basic features of the device, the results of both groups were cumulated. Easy handling, quick cleaning, being portable, providing footrests that are adjustable and allow fixing of the feet as well as offering an option to restrain the device in bed were regarded as must-be requirements. Note that the feature related to restraining the device in bed received equally high scores in two categories. In line with the Kano theory, this feature is therefore regarded as a must-be requirement. It emerged that the perception of the prototype along with type of movement and quick and easy installation were regarded as one-dimensional requirements. A method of feedback for the patient (such as a display showing the force or a step counter) was mentioned as a requirement that increases the attractiveness of the device.
The interviews highlighted three main categories, i.e. aspects considered most relevant by the physiotherapists: (i) quality of the exercise, (ii) installation and design of the device, (iii) hygiene.
The patient’s leg movement was perceived as physiological and relevant for early mobilization, with a clear focus on increasing leg muscle strength. In particular, the guided movement was considered important and well-suited for the target population. The pedal travel was rated as sufficient by six therapists while three users felt that it could be slightly longer, allowing larger movement. Pushing the foot pedal was judged as easier for the patient than pulling it (e.g. in a single leg training). Four therapists mentioned that extremely weak patients could have difficulty stabilizing their knees, potentially still requiring assistance from the therapists. The choice of three different training modes was regarded as appropriate. Setting the different modes and adjusting the resistance was perceived as simple and intuitive. One user commented: “…also the nursing staff could use the leg press with patients…”. Two therapists reported that “one of my patients really enjoyed training with the leg press”. In Group 1 it was mentioned that some form of motivating feedback would be interesting for the patient. Group 2, using the improved prototype, had the option to apply such a patient information system. One therapist reported that “the idea is great for mentally awake patients”, but that the handling of the additional parts (such as a cable-connected display) takes too much time to install and that different solutions should be considered.
Installation covers the process of positioning the leg press and the patient before the exercise can begin. Placing of the device in bed and the positioning and securing of the feet on the pedals were reported to be easy, quick and intuitive. The total weight of the leg press was rated as acceptable: the device was easy to carry and to store on the ward. Three users in Group 1 observed that the leg press moved in bed during exercise for some patients. The improved prototype used by Group 2 provided an attachment and this was commented on positively. Further, it was appreciated that no connections (e.g. to electricity or compressed air) are needed.
Regarding the design of the prototype, it was noted that “it is a visually pleasant device and it is not scary to use with patients”. The inclination of the foot pedals was found to be easily adjustable. The shape of the pedals was deemed suitable for different foot sizes and the fastening straps were reported to be a good fit. The heel area, however, was found to be potentially uncomfortable. Three users in Group 1 recommended that the pedals could be positioned at a steeper angle (90
With respect to hygiene, all physiotherapists commented on the importance of the device being quick and easy to disinfect after use. The users’ expectations in this regard were fulfilled by the prototype.
This study implemented a UCD process to develop a medical device. The starting point was the demand for an in-bed leg press for early mobilization in acute care settings. Since the demand was formulated by clinical staff in these units, their motivation was a driving force in the design process and they were involved throughout the process. This ensured that end-user needs were a guiding principle. The technical solution had to be as simple as possible. In particular, ease of handling was deemed a prerequisite to ensure the device will eventually be used in clinical practice. It is worth noting that there was an interprofessional interest in such a device. The nurses involved in this project were well aware of the complications following a prolonged period of bed rest (i.e. functional disability due to muscle weakness) and pointed out that such a device motivates patients and also enhances their own body perception. The UCD process, especially as it was interprofessional, afforded sufficient consideration to these views. However, as the primary users are expected to be physiotherapists, only physiotherapists tested the device with patients at this stage. Furthermore, the design team included researchers from relevant fields and engineers, which contributed to the quality of the development. The support of an industrial designer proved to be valuable, resulting in a prototype with a close-to-product look. An advantage of this was that we were also able to gain clinically relevant insights related to infection control. The high quality of the first prototype ensured that the testing focused on the relevant features in clinical practice and resulted in specific suggestions for improvement.
The process was evaluated by three measures: the SUS questionnaire, the Kano model and interviews. As expected, the application of the SUS questionnaire proved to be straightforward. Similarly, other studies have shown that SUS can be used for different types of system usability evaluation and can provide interpretable results even in trials with few participants [17]. In this project the German version of the SUS was used. Although this version is not validated, its use is assumed acceptable according to Gao et al. [18] and it is important to provide questionnaires in a language with which the participants are familiar. The in-bed leg press achieved in both applications a SUS score that can be rated as an “OK to good” usability according to Bangor et al. [12]. Despite not being statistically significant, the results of the SUS score demonstrated an increase that seems to be linked to the improvement of the prototype. As the modifications of the prototype were minor, the small increase of the score makes sense. The SUS seems sensitive enough to capture such incremental changes, which particularly holds true as the two groups were comprised of different therapists.
The SUS score in absolute numbers and its interpretation as “OK to Good” are more difficult to assess. The highly positive and enthusiastic views expressed in the interviews contrast with the SUS score to some extent. In the interviews, the participants mentioned that the leg press is simple and intuitive to use and in fact they did use the device correctly after only a brief introduction. Thus, a high SUS score was to be expected. However, it remains unclear whether participants generally responded more positively in an interview and/or rated the device more critically when using a given scale. There are indications that extreme responses are avoided in 5-point Likert scales [19]. Overall, SUS proved to be a helpful assessment tool in the UCD and allowed us to quantify the usability of the new device in a standardized manner.
In contrast to SUS, the Kano model requires more preparation because it addresses individual features of the specific device. As a result, the features are categorized based on the user assessment and thus the relevance of the features is prioritized. The application of the Kano model to the leg press confirmed several key features of the device (e.g. related to the exercise, handling, portability, attachment to the hospital bed, cleaning and foot pedals). These features must be offered otherwise users perceive the leg press as incomplete or poor [14]. As it is shaped to the specific device, the Kano model also highlights practical aspects. In our case, this related to, for example, the installation. The installation in bed must be quick and easy for the users (given that the device must be placed in bed with patients who have limited capacity to cooperate). It is remarkable, however, that the attachment to the bed was not clearly categorized as a must-be requirement. Apparently, the device can also be used without attaching the corresponding straps (its own weight allows for a stable positioning for some patients and/or certain exercises); not using them might save time on installation and is thus more practical. Similarly, the foldable foot pedals were classified as an optional requirement. During the development process, it was deemed a relevant aspect to provide foldable pedals to reduce the size of the device for storage. In practice, however, the pedals were apparently often not folded because this was not necessary for stowing. The infotainment system, with a step counter and a pressure sensor, was clearly classified as an attractive requirement. The Kano model as applied to Group 1 identified an option for further development, which was then implemented in the updated prototype. In summary, the Kano model offered the possibility to categorize different features and therefore added value to the development process. The results allow for the prioritizing of the various features, which is important for the final design as well as for future developments to improve the device.
Interviews are a commonly used qualitative method, particularly in medical research. In contrast to questionnaires, the interviews represent users’ views “unfiltered”. They can be regarded as the benchmark for other instruments, particularly if these are not fully validated. Since the interviews in this study were structured and based an interview guide, it ensured that all interviewees were presented with the same questions. This meant the interviews were comparable and allowed prioritizing of the statements despite the number of participants being limited. All physiotherapists agreed that the leg movement encouraged by the device is physiological and that a guided movement of the leg is important. The in-bed leg press therefore seems feasible. The three available training modes were regarded as being well suited for early mobilization. In addition, the training with the leg press and the corresponding leg movement, respectively, felt familiar to some patients from everyday activities. Physiotherapists reported that some patients really enjoyed the training, which in turn motivated the physiotherapists to use the leg press. This was a motivating stimulus for all involved.
The interviews with Group 1 raised the suggestion that a steeper angle for the foot pedals would be helpful. The optimum angle of the foot pedals depends on how the patient is positioned in bed whereas the position of the patient depends on their stature. The iterative UCD allowed for adjustment of this feature and then checking of its impact with Group 2. The user feedback was registered and evaluated within the design cycle. After the second series of tests the angle of the foot pedals was no longer criticized. However, the interviews also revealed that some features were controversial among the physiotherapists. The shape of the heel section of the foot pedals was reported to be uncomfortable by some patients. The foot pedals were produced by 3D-printing, which created the flat and hard surface, and patients can suffer from sore feet [20] or decubitus if they use the device for too long. Hence, the argument seems plausible. At the same time, some physiotherapists preferred the current solution and suggested using a small gel cushion in the heel area to increase comfort, or to provide patients with socks. Even wearing shoes is possible in the current design. This illustrates that a UCD does not necessarily lead to one optimum design but must synthesize different views. Ideally – as in our case – this is not related to core requirements but to implementation of minor aspects.
With regards to limitations, it must be noted that the study was performed during the COVID-19 pandemic. It can be assumed that the pandemic had an influence on the number of eligible patients in the ICU. For practical reasons, the number of users in the first and second round of tests was not the same because participation depended on who was available in the acute care setting during the given period. However, the instruments applied here are supposed to be robust enough to cope with these limitations. According to Nielsen et al., a usability test performed by only five users should be able to identify up to 80% of the potential issues of a device [21]. Thus, the number of participants in our study is regarded as sufficiently high; other UCD evaluations with fewer participants also showed meaningful results for device improvement [17].
Conclusion
This study demonstrated that a user-centered design approach can be implemented successfully in the development of a medical device, such as the development of an in-bed leg press. The early involvement of the interprofessional end-users resulted in a prototype that showed a high degree of production readiness. The resulting device fulfilled all core requirements from a therapeutic point of view and included key features related to its practical use. Instruments such as SUS and the Kano model allowed us to measure aspects of usability, desirability and feasibility during the design process, and also to document improvements based on end-user feedback. The application and evaluation of both questionnaires is efficient, but it is recommended to complement the assessment with interviews. In this project, the interviews provided further insights that proved to be valuable for the design process and this further strengthened the level of identification that the health care professionals held towards the new device.
Footnotes
Acknowledgments
The authors are grateful for the support of the nursing staff and the physiotherapists of the Department of Intensive Care Medicine as well as the staff of the Department of Infection Control at the Inselspital, Bern University Hospital. Furthermore, the support of BST Design was greatly appreciated. The authors also thank Ms. Rachel Pierce, Verba Editing House, for proof-reading the manuscript.
Conflict of interest
The authors have no conflict of interest at the time of submission. Options to develop the designed prototype into a future product are being explored.
Funding
The project was funded from own resources.