Discussion

Data synthesis

We saw evidence of some effect of the introduction of PDUs on our primary outcomes of informal acute psychiatric admissions and mental health presentations at ED but, given the complexity of the study, have an opportunity to use the full range of data we collected to better understand those findings. Synthesis of data from across WPs, developed through our synthesis workshop and subsequent discussion in the research team (as described in Chapter 2) produced the following set of ‘synthesising arguments’ that are indicative of our overall findings from the research (the analyses that support each argument are presented in Table 32). Note that these propositions are data-driven and as such do not always correspond directly to our initial research questions:

1. PDUs reduce overall levels of informal acute psychiatric admissions, but there is no clear trend in informal admissions after units open.
2. First time PDU visitors (about 40% of whom are relatively new to mental health services) experience increases in admissions of all types and community mental health service use in the months following their first PDU visit as they are connected with care and support (some service users report being able to access the care they need for the first time after their first PDU visit).
3. Following PDUs opening there is an increase in formal admissions (but with no clear trend in formal admissions after units opening).
4. There is little overall change in inpatient psychiatric service use as a whole after PDUs open, with no clear evidence of an effect on numbers of overall admissions, no evidence of change in bed occupancy or proportion of 0- to 5-day admissions (there is some evidence of reduction in average LOS), suggesting that PDUs might have a general impact on the balance of admissions away from informal and towards formal admissions.
5. There is little evidence of additional benefits of PDUs for people at high risk of psychiatric admission (i.e. people with previous admissions/diagnoses of psychosis), but there is evidence to suggest that PDUs provide a safe, calming environment) for people with a high level of acute need who might be too at risk for immediate discharge from ED but who are unlikely to benefit from an admission (PDU population is most likely to comprise this group, including people with diagnoses of mood or personality disorders).
6. PDUs can provide improved quality of care for this group of people (e.g. people with complex emotional needs) who might benefit from a PDU where there is a longer LOS with substantial opportunity for in-depth therapeutic input (including psychosocial interventions and higher staff-to-patient ratio) and onward referral/signposting to a wide range of community support.
7. PDUs have no overall effect on level or trend in mental health presentations at ED, but do have the potential to reduce presentations at ED where they are specifically set up to do so (i.e. higher capacity, shorter maximum LOS).
8. PDUs have no overall effect on liaison psychiatry episodes in ED, mental health presentations of people at risk of attending (people with previous attendances) or on 4-hour breaches or average length of wait except, potentially, where the PDU is specifically set up to impact mental health presentations in ED.
9. Conversely, while larger units with a shorter maximum LOS might be more likely to reduce pressure on ED, PDU staff can feel pressurised to admit inappropriate referrals and discharge service users while still feeling suicidal; referral and signposting to appropriate aftercare might also suffer where LOS on the PDU is shorter (i.e. configuring PDUs in this way, primarily to reduce pressure on ED, is unlikely to improve quality of care).
10. The effectiveness of PDUs in impacting either informal psychiatric admissions or mental health presentations at ED is associated with the aims of units and the way in which units are configured; in practice priorities for PDUs reflect trends in outcomes prior to PDU opening and the existence of other initiatives to address either psychiatric admissions or mental health presentations at ED.
11. A lack of clarity of function, differences in expectation and poor communication between PDU team and referral pathway staff, and inappropriate referrals mitigate the potential effectiveness of units; this reflects systematic review of the literature on similar units internationally which indicates that units with a clear purpose and configuration to impact ED wait times are effective in doing so, and units that primarily aim and are configured to reduce psychiatric admissions are effective in doing so (service users’ experiences of the crisis care pathway and of PDUs negatively impacted by a lack of clarity in unit function).
12. The impact of PDUs on cost to trusts of psychiatric admissions and ED attendances are marginal at most sites, resulting in only small savings; potential savings result from shorter length of psychiatric inpatient stay, and some site level savings relate to ED presentations and arrivals by ambulance compared to control but these do not offset cost of running PDUs (except at the BSMHFT site, where a substantial reduction in psychiatric inpatient LOS was observed in one analysis).
13. PDUs with a short LOS and low staff to patient ratio have considerably lower cost per visit (and can impact mental health ED presentations) than PDUs with longer LOS and higher staff to patient ratio (which can impact informal psychiatric admission and improve quality of care for people in crisis).
14. Significant additional costs of both inpatient and community mental health services are incurred by first time visitors to PDU as they are connected to care post first visit.
15. PDUs generally do not offer a simple financial return on investment in the short term, but the potential for reducing longer term costs of care as people access more appropriate community care (and less emergency care) and experience improved quality of life as a result indicate that PDUs may be cost-effective in at least some scenarios.
16. Changes in wider configuration of the crisis care pathway (e.g. introduction of street triage services) can support and reinforce the effects of introducing PDUs on both psychiatric admissions and ED mental health presentations (this was especially the case at BSMHFT, where a substantial reduction in length of psychiatric inpatient stay might be attributable to the introduction of an enhanced psychiatric liaison service).
17. Impact of changes in crisis care pathway on mental health presentations at ED are less clear (introduction of street triage and expansion of PDU provision to include psychosocial intervention reduced ED presentations in SWLSTG).
18. No overall evidence that PDUs might reduce inpatient admissions for sociodemographic groups over-represented in acute mental health care (although in one site, BSMHFT, indicated that, potentially, younger, male, non-White British service users might benefit from the introduction of PDUs); noting the exploratory nature of the analyses, costs of post-PDU care were generally higher for women and older people (i.e. people who already have better access) although cost of care was higher for non-White British service users in BSMHFT (people with insecure housing appeared to access less care post-PDU visit).
19. While working on the PDU can be rewarding and supportive for staff, the high-pressure nature of the role is also demanding and might mitigate the extent to which PDUs can provide higher quality of care.
20. Sustained benefits of PDUs (including where PDU visits are experienced positively) are likely to be mitigated by the capacity of crisis and community mental health services as a whole; where there are not sufficient appropriate options to refer or signpost for people (within mental health services and the wider community sector) or where the experience of discharge is hurried, then the potential longer-term effects of PDUs on ED presentations and psychiatric admissions might be diluted.
21. The pandemic did not have a major impact on the overall level of service use for people post first visit to the PDU, although there were often fewer face to face and more remote community contacts (compared with a similar pre-pandemic cohort), some reduction in CRHT team contacts and fewer inpatient admissions in rural areas (offset by increase in remote contacts).
22. The pandemic increased pressure on PDUs, even where there was an increase in capacity in the unit or other elements of the crisis pathway (e.g. the introduction of psychiatric ED provision), exacerbating many of the issues impacting quality of care described above.

Results in context

It is helpful to consider the implications of our findings in terms of the multilevel approach to addressing organisational research questions we proposed in Chapter 1,47 discussing the wider relevance of our findings at micro (individual), meso (service and organisational) and macro (policy) levels.

The psychiatric decision unit and individual experiences of crisis care

At the micro (individual) level, many people’s experiences of the PDU were positive, with the PDU described as a warm, caring, safe space offering time away from the stressors of everyday life, offering a considerably more supportive environment than the ED.12,14,27 Service users found staff kind and supportive, and appreciated opportunities to talk in depth in a way that had not often experienced in mental health services more generally.16 For many, PDUs offered a good balance between a safe, contained space, and a sense of freedom and being in control. However, both feelings of safety and of being supported were compromised where it was felt that staff were too busy or there was a lack of time to talk,16 or where people were discharged while still feeling suicidal or in distress.19 Staff also felt that the group of people for whom the PDU worked best – typically people who might receive a diagnosis of personality disorder – would benefit from a longer LOS, and at times they were discharging people too early. Mixed-sex spaces sometimes made women feel unsafe or anxious, and the presence of others in distress was could also be anxiety provoking.16

Many first-time PDU visitors were relatively new to mental health services and as such PDUs provided an entry point to care. Use of inpatient and community mental health care increased substantially for these people in the months following their first PDU visit, with some individuals reporting that it was only following their stay at the PDU that they received meaningful support for their mental health. While we were unable to follow-up these individuals for an extended period of time, being linked in to appropriate mental health care potentially reduces the need for crisis care and we saw liaison psychiatry episodes in the ED drop-in sites where there were the biggest increases in community mental health care use post-PDU visit.

The psychiatric decision unit environment, staffing and crisis care pathway

The way in which PDUs were configured and their place in the crisis care pathway at each site offered a meso-level perspective on the context of implementing PDUs into practice. Staff echoed service users’ experiences of the PDU as a calm, containing space that was preferable to the busy, chaotic environment of the ED. The use of recliners rather than beds met with a mixed response from service users, some people appreciating the fact that the unit did not feel like a ward, while others found them uncomfortable and disconcerting.

The journey to the PDU was experienced as straightforward for some, but challenging for others, involving uncertainty, waiting for transfer to the ED before eventually arriving at the PDU. As noted above, for some people the PDU worked well in linking them into appropriate care, but others, perhaps who had been using mental health services for some time, could find themselves discharged back to a level of care that had not hitherto worked to help address crisis, the PDU offering only a brief respite with no sustainable change to the way in which they were supported during a crisis.

PDU staff echoed these concerns, reporting pressure to take referrals of people who they felt were unsuitable to reduce pressure elsewhere on the pathway and having to discharge people home without the options or resources in the community to signpost them. Staff on the referral pathway could also express frustration related to a lack of clarity around who to refer or a feeling that expectation of the unit – to take pressure off the ED – had not been met. Co-location of the PDU with other services, typically the Section 136 place of safety could exacerbate these challenges. It is possible that these tensions and the resulting communication issues between staff teams contributed to a lack of clarity of function of the PDU.

On the whole, PDU staff teams enjoyed working on the units, reporting that the additional responsibility of working on a nurse-led unit and being able to take and challenge decisions enabled them to develop new skills. The additional time they had to spend with service users allowed them to work in more depth with people’s experiences of distress and to provide wider, social support. However, working continually with high levels of distress was emotionally very demanding and could lead to burnout and high staff turnover. The PDU staff team was experienced as highly supportive although team members did not always feel able to take advantage of the support available.

The psychiatric decision unit and mental health crisis care in England

Our findings have implications for policy-making in mental health crisis care in England, the macro-level, and therefore decision-making by commissioners and NHS trusts. PDUs, or their equivalents internationally, are not a new phenomenon, with units from North America94,95 and Europe96,97 dating from the mid-1990s. However, as noted in our mapping study, PDUs are far from ubiquitous in England with some MHTs decommissioning or repurposing PDUs (as wards) while other trusts initiate new units.82 As such, the jury is very much still out on whether or when PDUs offer a viable complement to the mental health crisis care pathway. Taken as a whole (and reflecting the international literature), our analyses suggest that PDUs can, and perhaps should, be clearly configured in such a way as to address, specifically, the primary crisis care need locally (in terms of our primary outcomes); that is, to reduce either unhelpful or avoidable informal psychiatric admissions,37,79,91,93 or impact mental health presentations at ED.40,79 The lack of clarity resulting from unit function sitting somewhere between the two objectives probably mitigates beneficial effect.

PDUs that successfully reduce informal psychiatric admissions have longer average lengths of stay (up to 40 hours), higher staff–patient ratio (approximately 1 : 2) and have a focus on therapeutic input, including delivery of psychosocial interventions and effective signposting to community resources. These units improve the experience and quality of crisis care, especially for people with a high acute level of need but who might not benefit from an inpatient admission,18 and reflect findings from the United States indicating the potential for PESs there to improve patient experience of crisis care.105,106 However, they are expensive to run and this cost is largely not offset by savings accrued from reduced admissions and shorter lengths of stay. It should be noted that resulting reductions in informal inpatient admissions were counterbalanced by increased formal admissions, with limited net change in inpatient service use. As such, the benefits of delivering PDUs in this way are largely associated with quality of care for a particular population that generally falls into a gap between the ED and psychiatric ward (typically people with diagnoses of personality disorders or complex emotional needs and/or people who had self-harmed who might not be best served by existing crisis and home treatment services).15 While in the short term this led to increased service use (and increased associated costs) for first-time PDU visitors, the PDU potentially acts as a gateway to more appropriate care for this population and, in the longer term, less costly use of crisis and acute care. In addition, we note that we did not assess reduction in non-healthcare costs that might accrue following PDU attendance, wider social benefits such as increased employment or improvement in mental health outcomes. Nor did we compare the effect of PDUs with that of triage wards,24,41 noting in our mapping survey that MHTs with PDUs were no less likely to have one or more triage wards than trust without PDUs. Our study did provide tentative evidence of significantly increased quality of life for people in the months following their first visit to PDU. If realised more widely, for the group of people for whom PDUs seem most suited – those with a high level of crisis need but who might not benefit from extensive inpatient and home treatment care – PDUs may well be cost-effective. As such, wider clinical and cost benefits are potentially understated here.

PDUs that successfully reduce mental health presentations at ED have shorter average LOS (around 12 hours), lower staff–patient ratio more akin to acute ward levels (approximately 1 : 4)42 and primarily address demand management issues on the ED when it is not safe enough to discharge someone to their home. Quality of care was not experienced as being as good on PDUs where people felt they were hurried to discharge before they were ready or were without sufficient opportunity to talk to staff in depth and where onward signposting was limited. However, given that numbers of mental health presentations at ED are high and continue to grow, PDUs that provided the high level of input described above would need to be extremely large and costly. This configuration is cheaper to run but again the cost is not offset by the savings resulting from reduced ED presentations (and do not reflect the more substantial savings estimated in studies internationally).90,97 The benefits are largely to the ED environment – reduced pressure on ED staff teams whose time would be freed up to attend to non-mental health patients104 – at sites where there was a reduction in mental health presentations or where wait times reduced.7,8,11,12 There is an inherent challenge for commissioners here in that these costs are met by the MHT in managing demand in the acute trust. In addition, it should be noted that the gains observed here often took place against a backdrop of increasing presentations or length of wait in the ED in England that have continued unabated since earlier reports were produced,9,10 and so were mitigating further increases in demand at best. It remains possible that alternative models, such as mental health assessment spaces directly attached to ED departments, offer a more effective and cost-effective approach to tackling ED wait times and in particular breaches of 4-hour wait targets in England.107

We have shown how impacts on both psychiatric admissions and ED presentations are best realised, and sustained, where the PDU complements other effective inputs into the crisis care pathway, including street triage,29 crisis cafes,31 crisis houses30 and enhanced psychiatric liaison services, whether as sources of referral to the PDU, alternative support or signposting options. The implications for policy and commissioning are that an interlinked network of crisis supports is necessary, reflecting local priorities and need,27,28 that over time might have a cumulative effect on demand on the ED and psychiatric inpatient care.

Equalities impact assessment

There is an established literature that indicates that people of black ethnicity, especially younger men, are over-represented in acute mental health care and under-represented in mental health services more generally,17,108 and we wondered whether PDUs might contribute to addressing these inequities by providing a pathway away from acute care and towards community-based support. We found some evidence that people referred to a PDU for the first time were younger than the MHT population as a whole, and limited evidence that they were less likely to be White British and more likely to be male. Analysis of increased cost of care post first PDU visit indicates that non-White British people were only accessing increased levels of care at one site (homeless people were failing to access increased levels of care post first PDU visit). While these findings were far from conclusive, they are perhaps indicative of some potential for PDUs and other crisis services, where they function as entry points to mental health care, to begin to address persistent inequalities if they are developed with that purpose in mind.

Impact of COVID-19

The beginning of ‘lockdown’ association with the COVID-19 pandemic coinciding with the follow-up period in our WP4 cohort study and WP5 qualitative interviews provided an opportunity to explore the impact of lockdown on mental health service use and experiences of crisis care.88 We observed very few differences between our pre-pandemic and primary cohorts (both were admitted to PDUs prior to lockdown) and perhaps surprisingly few differences in service use post-discharge from the PDU. There were no impacts on inpatient care and minimal impacts on the level of community mental health care, although the balance of community contacts shifted significantly from face to face to remote contacts. At some sites there was a reduction in contacts with CRHT teams. The pandemic did not impact on cost of care for people using PDUs.

In qualitative interview, staff reported an initial lull in referrals to PDU as the pandemic broke, but then an increase in demand, and range and severity of presenting issues, attributed in part to isolation and closure of community-based support groups. Some efforts were made to increase capacity of PDUs at some sites, although at one site the PDU was temporarily suspended as staff were assigned elsewhere. The temporary addition of a new mental health ED in one site led to pressure to constantly take new referrals. The combination of increased demand and changes to the crisis care pathway led to additional pressure on staff teams and higher levels of staff sickness.

Strengths and limitations

This was a quasi-experimental study, and as such individual workstreams are reporting using the Transparent Reporting of Evaluations with Nonrandomised Designs for non-randomised/quasi-experimental studies.109 We identified a range of limitations in the research, within and across WPs. Individual WPs analysed data from different time periods and different samples, and so not all of the comparisons we make in our data synthesis are direct triangulation between data sets. For example, because PDUs opened on different dates, WPs 2 and 3 are not synchronous across sites (interrupted time series and synthetic control studies cover the same time periods within each site). The WP4 cohort study and WP5 interview study were synchronous across sites, but as a result did not take place at the same time as ITS and synthetic control studies. In addition, because of availability of data, while the ITS analysed ED data from SGUHFT in SWLSTG and from SWBHFT, the synthetic control study used ED data from KHFT and UHBFT, respectively.

In our ITS study, we spent considerable time working with business intelligence staff within trusts to collect relatively precise data on both psychiatric admissions and mental health presentations at ED. However, data based on diagnostic coding, such as ED mental health attendances, may be more vulnerable to error, and mental health coding has been shown to be problematic in data sets derived from routine hospital data.110 In our synthetic control study, classification of ED data was determined by diagnostic coding or a ‘mental health reason for visit’ entry applied by staff in the ED. Admissions to mental health acute inpatient wards are also not explicitly coded as such in HES-APC and we proxied these admissions using the main specialty of the consultant or the treatment function of the episode (and might have included admissions to eating disorders or other specialist wards, or acute admissions to community-based crisis and home treatment teams, for example). Incidence of both our ED and MHT outcomes was substantially higher in the synthetic control study than the ITS as a result, potentially diluting or confounding effects and going some way to explaining differences in effects observed in the two studies.

However, within-site comparisons within each WP are all methodologically appropriate and clearly defined. While it is possible that effects observed in WPs 2 and 3 are at least in part explained by differences between comparators, conditions outside of trusts or by other changes in the delivery of care (indeed we explore this to some extent in secondary analyses in the ITS; see Chapter 4), creation of both the counterfactual in the synthetic control study and the extended time series in WP2 are methodologically robust and were risk-adjusted and included sensitivity analyses where possible.

There were some issues with data within WPs. In WP2, MHT data from Sheffield included a number of missing variables and there were missing data from large numbers of admissions during the times series period. As a result, psychiatric admission data from Sheffield were omitted from the interrupted times series analysis. In the WP3 synthetic control study, reporting requirements of MHT data to NHS Digital did not distinguish psychiatric admissions as formal or informal, capture liaison psychiatry episodes in ED or allow us to specifically identify outcomes for a population with previous admissions; hence we have a slightly smaller set of outcomes for the synthetic control study (compared with the ITS), without informal psychiatric admissions as a comparable primary outcome. Further, there were likely changes in mental health coding practice over the 4-year study period in participating sites, complicating interpretation of trends over time, and for a small number of variables in some trusts, data sets did not cover the entire 4-year period of interest; this decreased the power of corresponding WP2 ITS analyses and their impact in pooled analyses of outcomes.

The late addition of BSMSTG as a site to WP5 meant that we had no follow-up interview data for service users in BSMSTG and could not explore the post-discharge pathway there. We did collect sufficient baseline data from service users, as well as a range of PDU and pathway staff data, to sufficiently explore the model of care in BSMSTG. We were unsuccessful in recruiting a diverse service user sample to WP5; as a result, we did not systematically capture the experiences for black, Asian and minority ethnic visitors to the PDU and were unable to further elucidate findings from our equalities impact analysis in WP5. In WP6, because we relied on patient record data and did not directly recruit and follow-up a cohort of PDU visitors, we did not have sufficient structured quality-of-life data to formally assess cost benefit in terms of quality of life-years (although data we collected from WP5 participants did enable us to include quality of life in our modelling work). Our whole study design was predicated on a synthesis of routinely collected service use data and experiential insight from qualitative interview. This offers an extremely cost-efficient approach to research but as a result we missed out on participant reported outcomes (including quality of life) that are collected through (costly) one-to-one interview.

Nonetheless, our mixed-methods approach46 was a strength of the study as a whole. Given that an experimental study design was not practical, employing two robust quasi-experimental methods offered both within-site and externally controlled estimates of effect enhancing confidence in our findings. The critical synthesis method made systematic use of data from across WPs to generate and explore potential explanatory arguments that might usefully inform research, policy and practice, rather than prioritise and discount analyses solely on the basis of reliability. The inclusion of a cohort study enabled us to explore the impact of PDUs on service use at an individual level while qualitative research, with staff and service users, was indicative of the complex relationship between experience (quality) of care and clarity of purpose of PDUs, and the potential effectiveness of different configuration units. As a result, we were able to give carefully consider if and how different configurations of PDU, in the context of the crisis care pathway as a whole, impact outcomes in different ways, providing us with opportunity to draw nuanced conclusions on PDU configuration in relation to policy and efforts to manage demand on services across acute and mental health NHS trusts that would not have been possible without our mixed method and critical synthesis approach.

Impact of patient and public involvement on the research

There were a number of important impacts of patient and public involvement and of our coproduced approach to research on the study and findings:

• First, and importantly, in a study where most WPs were quantitative in nature, reducing research questions to measures of service activity, the qualitative WP – where the was most patient and public involvement input – was essential to the interpretation of data.
• Researchers working from lived experience on the team and through the LEAP ensured that the experiential perspective on PDUs remained front and foremost throughout the study, and particular as we began to analyse and make sense of all of our data.
• This insight, together with that of the PEER group who helped develop the study and the lived experience researchers on the team, ensured that our qualitative interview questions were very specifically focused on key aspects of the experience of mental health crisis and of staying on a PDU.
• The lived experience researchers, with input from the LEAP at our interpretive and synthesis workshops,48 also emphasised key aspects of the data that play a crucial role in shaping our data synthesis and overall conclusions. This work underscored: the high levels of suicidality among visitors to the unitsthe importance of both unit environment and the depth of talking and listening required of unit staff to impact such levels of distressthe crucial importance of having sufficient time on the unit to begin to address issues for peoplethe sense that the impact of the unit was wholly mediated by the capacity of the crisis pathway to continue to support people post-discharge.

These understandings provided a lens through which to make better sense of the balance of impact, cost and benefit of introducing PDUs.

After discussion the lived experience team decided on overt disclosure of their lived experience to people they were interviewing in WP5, both in participant information sheets and in introduction to the qualitative interview. At the end of the interview two questions were asked about what it had been like talking with a researcher with lived experience and whether the interviewee thought this had made any difference. An in-depth analysis of these responses will be the subject of future publications, but a preliminary analysis suggests a marked impact in terms of ease of talking, ability to share difficult experiences, and feelings of being listened to, heard and believed from service user participants.

The co-investigator responsible for supporting the patient and public involvement in the project facilitated regular reflective sessions for the researchers with lived experience. This gave the team an opportunity to openly reflect and gain support in a safe environment about the experience of using their lived experience in the project and of the impacts it had had on them. This was particularly important as many of the interviews including accounts of distressing experiences and feelings of suicidality. It was also an opportunity to continuously reflect and monitor on how patient and public involvement was being used in the study and what was working well and what could be done differently.

Recommendations for future research

Recommendations for future research are both methodological and substantive in nature. While our study benefited from employing a number of different approaches to estimating the impact of introducing a new service model on mental health and ED service use, there is need for research to better understand how the way in which data are coded in national data sets impact the specificity and precision of estimates, especially with MHT data, and how to best interpret differences in estimates obtained from proxies for specific populations derived national data sets and directly from electronic patient record. This understanding would help in the efficient design of studies of service-level/pathway change in the future where a quasi-experimental approach is most appropriate.

In our study we relied on a combination of service use and qualitative, experiential data. We did not assess individual-level clinical or psychosocial outcomes, in part because recruiting a large cohort to do so adds considerable cost to the research and a clear rationale is needed for doing so. However, as a result we struggled to obtain sufficient quality-of-life data and potentially missed out on outcomes that would have shed more light on quality of care (which emerged as important in our qualitative analysis) and provide more conclusive evidence on the potential cost-effectiveness of PDUs. Future research might usefully build on our study to target a group or groups of people who might reasonably be expected to benefit from PDUs and evaluate the impact on a wider range of mental health and psychosocial outcomes, either using an experimental or quasi-experimental design. Alternatively, more attention might be paid to the use of routinely collected patient reported outcome and experiences measures, such as, for example, DIALOG+,111 to enrich our understanding of the impact of service-level change. Further research might also usefully refine, methodologically, a longitudinal approach to qualitative enquiry about experiences of care pathways.

While we were able, in our equalities impact work, to demonstrate some potential for PDUs to impact access to care for underrepresented groups, we did not manage to systematically integrate this work across workstream. Future research might develop, a priori, analysis plans that better explore associations between demographics and outcomes as we did in our cohort study and health economic analyses, while sampling for qualitative research needs a more proactive approach in order to obtain meaningfully diverse samples.

Our study revealed the challenges around evaluating the impact of the introduction of a new service model in the context of an evolving care pathway where other service-level initiatives are also likely bring about change. While we demonstrated some success both in isolating effects and identifying complementary effects, there is a need for a systems-level approach to investigating mental health crisis care building on similar studies elsewhere,50,112,113 including the role that the third and voluntary sector might best play in providing an effective network of crisis support.32 As designed, our study also lacked an economic perspective on the commissioning and decommissioning of other crisis care services alongside our PDUs. Such an approach might usefully be applied to similar policy driven initiatives that seek to change the wider landscape of health and social care.

We did find evidence that suggested that PDUs might be an appropriate approach to crisis care for a particular group of people (those likely to receive a diagnosis of personality disorder or be identified as having complex emotional needs and/or who experience self-harm) whose needs fall between existing types of acute and community care. This group of people often have underlying experiences of complex trauma that are unmet by mental health services,114 and there is an opportunity for the PDU to identify need and signpost people to more appropriate therapeutic as well as crisis care. Further research would usefully explore in depth the relationship between experiences of trauma and access to appropriate mental health care for this group.

Implications for policy and practice

Our research implies that PDUs make a potential contribution to the mental health crisis care pathway when integrated alongside other service options in order to address specific local need. PDUs should be appropriately commissioned and configured with clear objectives of either: alleviating increasing demand in the ED; or improving the quality of crisis care for people with high levels of acute need who are unlikely to benefit from an inpatient admission. In the case of PDUs designed to support the ED, while these are likely to have higher capacity and higher turnover, more needs to be done to ensure that units do offer a better environment and better quality of care that the ED, with sufficient levels of staffing to ensure that people are not discharged while still feeling suicidal. In the case of units designed to provide an alternative to inpatient admission, LOS needs to be long enough to support the client group with training provided to staff to provide effective psychosocial input. PDUs might also improve access for people who experience inequalities of access to care, although this should not be assumed, with more needed to be done to develop PDUs and care pathways with this in mind. While PDUs have the potential to reduce costs associated with ED mental health attendances and psychiatric admissions these are unlikely to offset the cost of operating the units, and so commissioning should not be primarily financially driven. However, where PDUs are successful in improving access to appropriate care (where there is an effective range of community resources to which to signpost people on discharge), over the longer term it is possible that demand on crisis and acute care, and associated costs, are further reduced.