Fourteen healthcare professionals were purposively invited. Three healthcare professionals declined the invitation due to time constraints (N = 1) and absence during the study period (N = 2). Subsequently, 11 healthcare professionals participated in the interviews. The mean interview duration was 44 minutes (range 21–60). Thirty-seven of the 48 healthcare professionals responded to the questionnaire (response rate 77.1%). Those participating in the interviews and questionnaire consisted of at least one nurse and one physician from the five outpatient clinics. The characteristics of the participants can be found in Table 1. The majority of the interviewees (9/11) also completed the questionnaire.

In line with other research [18], two open-ended questions were added to the MIDI. These were: “Do you have any tips or suggestions for improving the ACP conversations?”, and; “If you have any comments, please describe them here”. Additionally, respondents were asked to describe other personal benefits and drawbacks in addition to the benefits/drawbacks mentioned in the MIDI. Respondents were also able to add a comment to all questions within the questionnaire. Moreover, several questions were adapted. Within question seven (“relevance for client”), we have differentiated between patients (7a) and their proxies (7b). The answer options to question eight (“personal benefits/drawbacks”) of the MIDI were based on the barriers (disadvantages) and the facilitators (advantages) mentioned during the interviews. Within question nine (“outcome expectations”), we have differentiated between three outcome expectations based on the definition of ACP by Rietjens et al. [1] Within question ten (concerning professional obligation), we have differentiated between the responsibility of the healthcare professional, that of the hospital, and the importance of involving a physician. Question 18 (“To what extent are you informed about the content of the innovation?”) was removed. Within question 20, concerning replacement of staff leaving the organisation in a timely manner, we have differentiated between staff (healthcare professionals) conducting the ACP conversations (20a) and staff supporting in the organisation of the intervention (20b). Within question 23, concerning availability of time, we have differentiated between having sufficient time for introducing and inviting the patient to the intervention (23a), and having sufficient time to conduct the ACP conversation (23b). Within question 25, we have asked about the accessibility of the coordinator instead of asking whether a coordinator was present. Within question 26 (“unsettled organisation”), we added the Covid-19 pandemic (26a) next to the influence of other projects (26b). The revised questionnaire can be found in Table 2.

An overview of the barriers and facilitators identified by the modified MIDI can be found in Table 2. Eight barriers and 20 facilitators were identified. The barriers to implementation of the MUTUAL intervention were identified within the user (three barriers), and the organisation domain (five barriers). The facilitators were identified within the intervention (six facilitators) and the user (14 facilitators) domain. The content of the interviews and the answers to the questionnaires are used for clarification and illustration of the barriers and facilitators throughout the result section. Illustrating quotes from the interviews are presented in Table 3. The barriers identified, and the associated suggestions for improvement, can be found in Table 4. Since the facilitators are identified within the intervention and user domain (the first two domains within the MIDI) we will present the facilitators first.

The facilitators related to the ACP intervention were its “clarity”, “correctness”, “completeness” and “simplicity”. Additionally, facilitators concerning the intervention were “relevance for patients” (97.2% agreed) and “relevance for their proxies” (94.6% agreed). Interviewees expressed the relevance of the ACP conversations by stating that these were believed to be valuable and that patients appreciated having them (Table 3, quote 1). Moreover, ACP conversations are mentioned as a means of helping to get to know patients better and understanding what is most important to them (quote 1 and quote 2). These conversations were also believed to help in making informed, and shared decisions (quote 3).

Fourteen facilitators were identified in the user domain. These included two personal benefits: the ACP intervention helps healthcare professionals to improve the quality of care (94.6% agreed) and it helps to understand patient wishes (91.7% agreed). Within the interviews, ACP conversations are reported to affect patient encounters beyond the MUTUAL intervention (quote 4), hereby improving the quality of care.

Within the MIDI, the advantages 8f (“make me feel satisfied”) and 8 g (“contribute to personal development”) have not been identified as facilitators (75.0 and 61.6% agreed, respectively). In the questionnaire, the advantage of personal development is described as follows: “ACP conversations contribute to my personal development, conversing about the value of illness and health is meaningful in all encounters with patients.” This corresponds with the interviews, in which ACP conversations are mentioned as being fulfilling (quote 5) and contributing to personal development (quote 6). A separate analysis of responses from nurses in the MIDI showed that 85.7% agreed that the ACP conversations are satisfying and 85.7% also agreed that these contribute to their personal development. Another advantage mentioned within the questionnaire is that the ACP intervention “creates a fixed moment where patient and proxies are able to discuss important issues”. Other personal benefits of the ACP intervention mentioned during the interviews include that they “improve patient connection”, “improve follow-up conversations”, “save time in the long run”, “make me feel satisfied”, and “help in structuring ACP conversations”.

Three facilitators in the user domain were related to outcome expectations. Healthcare professionals expect that the ACP intervention “enables the patient to formulate goals and preferences for future medical treatment and care” (90.9% agreed), “enables the discussion of goals and preferences with family and healthcare professionals” (100.0% agreed) and “leads to the documentation of treatment preferences” (97.0% agreed). Nine other facilitators fell within the determinants “professional obligation”, “patient satisfaction”, “normative beliefs”, “self-efficacy”, and “knowledge”. Of the respondents, 93.9% agreed that “ACP conversations are the responsibility of their profession” and 81.8% agreed that “a physician should always be involved in the ACP intervention”. Among respondents, 87.9% agreed that “patients are generally satisfied with the ACP intervention” and 87.9% of the healthcare professionals agreed that they “have sufficient knowledge to use the ACP intervention correctly”. Interviewees mentioned the relevance of various elements of the MUTUAL intervention. The preparatory questionnaire, for instance, was mentioned as a facilitator for the ACP conversations since it helped the patient to understand the goal of the conversation and hereby facilitated the conversation (quote 7).

Three barriers lay within the user domain. Firstly, the intervention is perceived as demanding by 27.8% of the healthcare professionals and raises the workload according to 44.4%. Additionally, 39.4% of the participants reported that “less than half to not a single colleague from my specialty use/uses the ACP intervention”. The quotes from the MIDI illustrate the potential burden on healthcare professionals, and reflect on the alternatives. One healthcare professional commented: “Documentation of the ACP conversation takes a lot of time. There is no time reserved within the outpatient clinic schedule for documentation. It [the ACP intervention] takes a lot of time, including preparation, documentation, etc.”, and: “Time investment [is high], however, otherwise these [ACP] conversations should take place without reserved time, which is less desirable.” Interviewees mentioned that gaining more experience makes the ACP conversations less demanding. Uncertainty concerning who should be responsible for initiating ACP conversations, and the limited cooperation between the general practitioner and hospital physicians, were mentioned in the interviews as potential barriers. Moreover, it was mentioned that the division of tasks seems less clear when patients have multiple comorbidities requiring them to be seen by several physicians.

The most important barrier mentioned during the interviews was a lack of time. It was suggested that this impedes the implementation of the intervention in several ways. For example, healthcare professionals mentioned that there was not sufficient time to introduce and invite the patient to an ACP conversation during the regular visits at the outpatient clinic (quote 8). This is confirmed by the results of the MIDI which showed that 25.0% of the healthcare professionals disagreed that there is sufficient time for introducing and inviting patients to such ACP conversations at the outpatient clinic. When analysing the results separately for the physicians who are responsible for introducing and inviting patients, this barrier is even more outspoken (39.1% disagreed). Moreover, 22.9% of the healthcare professionals disagreed that there is replacement in a timely manner when healthcare professionals responsible for conducting ACP conversations leave (quote 9). Furthermore, 26.5% disagreed that there is sufficient staff capacity for implementation of the ACP intervention. Additionally, planning the ACP conversations can cause problems. This is reflected in a comment in the questionnaire that read, “Planning a conversation in a multidisciplinary setting (with nurse and physician) is sometimes difficult”. Moreover, it is mentioned that it is more difficult to plan ACP conversations if no regular timeslots have been reserved within the normal schedule of the outpatient clinic.

Two barriers are related to there being an “unsettled organisation”. Among the participants, 78.4% of the participants agreed that Covid-19 influences the ACP intervention. For example, healthcare professionals mentioned that they were reluctant to invite patients to have ACP conversations due to the risk of exposure to Covid-19. Additionally, 27.3% of the participants responded that other projects within the hospital influence the ACP intervention.

Another barrier mentioned in the interviews is the uncertainty of the effect of the ACP intervention (quote 10). Healthcare professionals explain that they are not aware of the continuation of the patient journey and neither are they convinced that other healthcare professionals are sufficiently aware of the documentation of the ACP conversations. However, the lack of effect of ACP is not a barrier within the MIDI. Of the healthcare professionals, 8.3% disagreed that the outcome of using the ACP intervention is clearly observable (52.8% agreed). However, the interviewees mentioned that if they are informed of the positive effect of the ACP intervention, then this is a facilitator and motivator (quote 11). All healthcare professionals report in the interviews that a lack of awareness and a gradual drop in attention afforded to the ACP intervention once it has begun, is a barrier to the implementation of the ACP intervention. Moreover, within the interviews and questionnaires, the importance of organisational support is stressed (quote 12).

Several suggestions for improving the implementation of the MUTUAL intervention were made. These included making ACP conversations less demanding (e.g., help with skills development) and decreasing the workload (e.g., administrative support). A lack of time was mentioned as a barrier in several ways, including the lack of time to introduce and invite patients. Various suggestions to expand the way patients are to be invited for an ACP conversation were made. These included creating an opportunity for other healthcare professionals, for example nurses or paramedical staff on wards or at outpatient clinics to be involved, structurally, in the selection process. Another suggestion was to incorporate discussions on the selection of patients into the structure of other meetings, including multidisciplinary ones. The barriers identified by the MIDI and the associated suggestions for improvement, can be found in Table 4.