Interrupted time series

Psychiatric decision units: structural characteristics and patterns of activity

Activity patterns and attendee characteristics from the first 2 years of PDU operation in each site are shown in Table 9. The number of PDU attendances was highest in BSMHFT, which has the largest capacity (eight) and several referral routes. Attendances were much less frequent in SHSCFT PDU, although the unit was closed for a 10-week period during 2020. Units were attended by a small majority of female service users, except for BSMHFT, where there was an even split between men and women. The distributions of attendees’ ages were comparable across sites, reflecting a tendency for about three-quarters of attendees to be aged 25–64 years. LOS on PDUs was longest for SWLSTG and shortest for LPFT. Precise LOS was not available for BSMHFT, although 43.4% and 39.4% of attendees, respectively, were discharged on the same day as admission or the next day, suggesting a relatively short LOS for most attendees. There were marked differences in the proportion of attendees subsequently admitted to psychiatric inpatient wards, ranging from just under one-third in LPFT to less than one in 10 in SHSCFT.

There were notable differences in the trajectories of attendance frequencies over the initial 24 months in each site (see Appendix 4, Figure 16). The number of attendances grew over the first 3 months post PDU implementation in BSMHFT, LPFT and SWLSTG sites but was steady thereafter for LPFT (70–80/month) and SWLSTG (50–60/month); in contrast, attendance levels in BSMHFT increased markedly from months 11–14 and afterwards the PDU maintained over 100 attendances/month. The frequency of attendances in SHSCFT was low initially, steadily climbing to 40/month by month 8 and largely maintaining that level thereafter aside from the closure period in March to June 2020.

Mental health trust outcomes

The catchment populations, annual rates and user characteristics of adult acute inpatient admissions and PLEs for each participating MHT, stratified by pre and post PDU implementation periods with pairwise comparisons, are described fully in Appendix 4, Table 34. Reliable data on inpatient admission and psychiatric liaison activity could not be sourced from SHSCFT and consequently they are not provided here nor included in subsequent ITS analyses.

In general, inpatient admission and PLE activity levels were considerably greater in BSMHFT (1772/year, 7446/year, respectively) and SWLSTG (1578/year, 4195/year) than LPFT (630/year, 1719/year). The frequency of inpatient admissions was comparable between pre and post PDU periods for BSMHFT and SWLSTG but higher in the latter period for LPFT. Across all trusts, the number of PLEs were significantly higher in the post PDU period. Individuals with previous (in last 24 months) inpatient admissions and PLE activity, respectively, made up a notable proportion of admissions (36.8–44.3%) and PLE (33.8–48.1%) in the study period, with a significant increase from pre to post PDU periods for the latter. There was a high proportion of women admitted to inpatient wards in SWLSTG (almost half) relative to BSFMHT and LPFT (40–45%). The (broad) distributions of age were more comparable, with approximately four of five admissions of service users aged 25–64 years. Overall, informal admissions made up about half of the admissions in BSMHFT and SWLSTG and over 60% in LPFT, although all trusts observed a significant post PDU decrease in the proportion of admissions that were informal. Length of inpatient stay was highest in BSMHFT where only 1 in 10 service users admitted stayed 5 days or less and lowest in SWLSTG where 1 in 5 had short stays. In the post-PDU period, length of inpatient stay increased in SWLSTG and LPFT as indicated by significant changes in median days and/or decreased frequency of 0- to 5-day stays, but there was a small but reliable decrease in LOS in BSMHFT. Daily bed occupancy significantly increased in the post-PDU period for all trusts where data were available. Out-of-area admissions, available for SWLSTG only, showed a marked decrease (from 75.5/ to 47.0/year) following PDU implementation.

Interrupted times series outcomes: psychiatric inpatient admissions and psychiatric liaison episodes

Weekly aggregated data concerning the frequency of informal acute adult inpatient admissions in pre and post PDU periods in participating MHTs are presented graphically in Figures 8–10. Corresponding parameter estimates from ITS analysis and estimates for secondary outcome measures are shown in Tables 10–12 (see Appendix 4, Figures 17–36 for accompanying graphical depictions).

FIGURE 8 Impact of PDU implementation on informal inpatient admissions in BSMHFT. Note: The black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Inpatient admission and psychiatric liaison episode activity in Birmingham and Solihull Mental Health NHS Foundation Trust

Data indicate a significant decrease in the number of informal admissions immediately following PDU implementation (by 16%) but an increase in informal admission rate in the post PDU period (of 0.33%/week; see Figure 8, Table 10). There was a smaller (non-significant) drop in informal admissions upon implementation of the PDU for those with a recent previous admission, but a similar, reliable post-PDU increase in admission rate. These findings were mirrored by a significant increase in the proportion of formal admissions immediately after PDU implementation (from 52% to 58%) but a steady decrease in the weekly proportion of formal admissions in the 2 years following PDU implementation, reflecting a highly significant change in rate from pre to post PDU.

While there was no effect (either short- or long-term) of the PDU on overall admission rates or on admitted service users’ length of inpatient stay, there was a significant difference in trend of daily bed occupancy between pre and post PDU periods, reflecting a shift from a pre-PDU increase of 0.15 beds/week to a more stable pattern of daily bed occupancy post PDU (decrease of 0.03 beds/week). PLE frequency in the pre-PDU period was significantly increasing, by 0.24%/week, but decreased immediately following PDU implementation (by 10%). There was no significant change in the underlying increasing weekly trend post PDU, however, with PLE frequency continuing to increase (by 0.21%/week) in the post-PDU period. However, there were highly significant short- and long-term decreases in weekly frequency of PLE considering episodes by individuals with a recent previous episode, albeit in the context of an increasing weekly pre-PDU trend in this group of service users.

Inpatient admission and psychiatric liaison episode activity in Lincolnshire Partnership NHS Foundation Trust

The weekly frequency of informal admissions decreased immediately following PDU implementation by more than 10%, although this failed to reach significance (see Figure 9, Table 11). Nevertheless, there was a significant (long-term) change in pre- to post-PDU trend; in the 2-year post-PDU period, the number of informal admissions decreased by almost half a per cent/week. A similar pattern emerged (at a monthly level) considering only those informal admissions by service users with a recent previous admission. Prior to PDU implementation, weekly admission (formal and informal) frequency was increasing by 0.29%/week. This pattern was reversed in the post-PDU period where admissions decreased significantly by 0.18%/week, representing a highly significant change pre- to post-PDU trend (of 0.45%/week). The proportion of admissions that were formal was significantly increasing each week before PDU implementation. There was a further (immediate) increase (from 30% to 40%) on PDU implementation, and the pre-PDU trend continued in the post-PDU period pattern at the same rate (increase of 0.14% points/week). The PDU had less impact on length of inpatient stay, although the proportion of short stays, which was increasing prior to PDU implementation, did stabilise in the post-PDU period. There were significant trends during pre- and post-PDU periods indicating increasing PLE frequency, although when considering only those episodes by individuals with a recent previous episode there was a significant pre- to post-PDU trend decrease in (monthly) episode frequency.

FIGURE 9 Impact of PDU implementation on informal inpatient admission in LPFT. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Inpatient admission and psychiatric liaison episode activity in South West London and St George’s Mental Health NHS Trust

Prior to PDU implementation, there was a significant trend indicating an increase (of 0.27%/week) in informal admission frequency. Informal admissions decreased by almost 20% immediately following implementation of the PDU, and there was a highly significant change in pre- to post-PDU (long-term) trend, reflecting a decrease of 0.5%/week (see Figure 10, Table 12). The effect of the PDU on informal admissions for service users with a recent previous admission was very similar, although the post-PDU trend also indicated a significant weekly decrease. A significant change of weekly trend from pre- to post-PDU periods was also observed when considering all admissions (formal and informal), suggesting that PDU implementation arrested the prior trend of increasing admission frequency. The opening of the PDU in SWLSTG had an immediate impact on the proportion of patients admitted formally (increase by almost 7% points, from approximately 43% to 50%) and there was a significant change (weekly increase) in the pre- to post-PDU trend. There was little indication of an effect of PDU implementation on length of inpatient stay or daily bed occupancy rates over the study period. In a similar manner, there was no significant impact of PDU implementation on PLE frequency, which was increasing over the pre-PDU period (both for all service user episodes and for those by service users with a recent episode).

FIGURE 10 Impact of PDU implementation on informal inpatient admissions in SWLSTG. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Acute trust outcomes

The catchment populations, annual rates and user characteristics of ED mental health attendances for each participating acute trust, stratified by pre- and post-PDU implementation periods with pairwise comparisons, are described fully in Appendix 4, Table 35. In general, attendances were more frequent in SWBHFT (2242/year) and STHFT (2200/year) than SGUHFT (1980/year) and ULHFT (1620/year). Annual rates were comparable between pre- and post-PDU periods in SWBHFT and in SGUHFT but higher in the latter period for LPFT and lower post PDU in STHFT. A small majority of attendances in SWBHFT (55.1%), SGUHFT (61.1%) and STHFT (62.9%) were by service users who had previously attended (for any reason) in the last 24 months; there was a marked decreased in STHFT from pre (67.0%) to post PDU (53.8%), however. The overall proportion was much lower in ULHFT (34.4%) most likely because these attendances considered only those individuals with previous attendances involving a mental health presentation.

The sex of attending service users was, overall, evenly split between women and men in STFHT, SGUHFT and ULHFT but women only made up 39.5% of the attendees in SWBHFT over the study period, although this significantly increased post-PDU implementation. Approximately two-thirds of service users were aged 25–64 years in STHFT and ULHFT. This compared with three-quarters of attendees in SGUHFT, although the proportion of younger service users (aged 18–24 years) significantly increased post PDU. In all trusts, more than half of ED mental health attendances were by individuals arriving by ambulance or police. This was particularly apparent at ULHFT (66.8%), although there was a significant reduction in ambulance/police arrivals post PDU. Rate of admissions to an acute trust ward from ED was also higher in ULHFT (19.6%) relative to other trusts (8.6–12.7%) where significant decreases in acute trust ward admissions in the period following PDU implementation were observed. Median LOS for ED mental health attendances varied between 3 and 4 hours, depending on the trust, with 4-hour breach rates ranging from just under one-quarter in SWBHFT (23.8%) to almost 40% (39.2%) in ULHFT. While length of ED stay significantly decreased from pre to post PDU in SWBHFT, STHFT and ULHFT, it increased in SGUHFT. Further, the proportion of 4-hour breaches significantly increased post PDU in SGUHFT (by 2.4% points) and ULHFT (by 5.0% points).

Interrupted times series outcomes: emergency department mental health attendances

Weekly aggregated data concerning the frequency of ED mental health attendances in pre- and post-PDU periods in participating MHTs are presented graphically in Figures 11–14. Corresponding parameter estimates from ITS analysis and estimates for secondary outcome measures are shown in Tables 13 and 14 (see Appendix 4, Figures 37–52 for accompanying graphical depictions).

FIGURE 11 Impact of PDU implementation on weekly number of ED mental health attendances in SWBHFT. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Emergency department mental health attendances in Sandwell and West Birmingham Hospitals NHS Foundation Trust

The data indicate that prior to PDU implementation, there was a highly significant increase in ED mental health presentations in SWBHFT (by approximately 0.5%/week). There was a significant decrease in the number of ED mental health attendances immediately following PDU implementation (by around 20%) but there was little impact on long-term trend, and ED attendance frequency continued to rise in the post-PDU period (by 0.4%/week; see Figure 11, Table 13). The pattern was similar when considering only those attendances by service users with a (recent) previous ED attendance, although the initial period was characterised by a more marked weekly increase in frequency (by approximately 0.8%/week) and there was a significant change (decrease) in trend from pre to post PDU. There was little impact of PDU implementation on the proportion of ED mental health attendances via ambulance or police or rates of 4-hour breaches, although there was a significant drop (> 10%) in length of ED stay immediately following PDU implementation. Curiously, the proportion of ED mental health attendances discharged to an acute trust ward decreased significantly in the period before PDU implementation but increased by about 4% on opening of the PDU, although was still steadily declining in the post-PDU period.

Emergency department mental health attendances in United Lincolnshire Hospitals NHS Foundation Trust

While there was no evidence of an immediate effect of PDU implementation on ED mental health attendances in ULHFT, there was a significant increase (by 0.3%/week) in attendance frequency in the post-PDU period, reflecting a change in pre- to post-PDU trend (see Figure 12, Table 13). PDU implementation had no significant short- or long-term effects on the proportion of ED mental health attendances where individuals arrived by ambulance or police, which was significantly decreasing in the pre-PDU period. There was, however, a significant increase from pre to post-PDU in the proportion of attendances where service users were discharged from ED to an acute trust ward, reversing the decreasing pre-PDU trend. There was evidence for a small but reliable weekly increase in (mean) LOS in ED following PDU implementation but no effect on 4-hour breach rate.

FIGURE 12 Impact of PDU implementation on weekly number of ED mental health attendances in ULHFT. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Emergency department mental health attendances in Sheffield Teaching Hospital NHS Foundation Trust: interrupted time series outcomes

There was a pre-PDU trend indicating a significant decrease (by 0.16%/week) in ED mental health attendances. There was a non-significant decrease in attendance frequency immediately following PDU implementation but a significant increase in pre- to post-PDU trend over the longer term (a single year post PDU in the case of STHFT), although weekly attendances did not increase in the post-PDU period (see Figure 13, Table 14). These effects were in the same direction, although more marked, when considering only those attendances by individuals with a recent ED attendance. In the pre-PDU period, the proportions of mental health presentations in ED where individuals arrived by ambulance or police and/or were discharged to an acute trust ward were decreasing significantly. However, following PDU implementation, significant short- and long-term increases in the rate of arrivals by ambulance or police and a significant increase in pre to post trend for attendances with discharge to acute trust ward occurred. LOS in ED was also significantly decreasing prior to implementation of the PDU, both with respect to (mean) minutes in ED and proportion of 4-hour breaches, although there was no significant (short- or long-term) impact on this trend following PDU implementation.

FIGURE 13 Impact of PDU implementation on weekly number of ED mental health attendances in STHFT. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Emergency department mental health attendances in St George’s University Hospital NHS Foundation Trust

There was little evidence for either an immediate or long-term effect of the introduction of the PDU on attendances in SGUHFT. There was a small but reliable decrease (of 0.06% points/week) in the proportion of attendances where individuals arrived via ambulance or police in the post-PDU period (see Figure 14, Table 14). The rate of ED attendances with discharge to an acute trust ward increased significantly following PDU implementation and there was a highly significant change in pre to post PDU trend, although the proportion remained in steady decline in the post-PDU period. Average LOS in SGUHFT ED increased in the post-PDU period (by approximately 0.2%/week), significantly reversing a pattern of decreasing LOS prior to PDU implementation, although there was little evidence for an impact of the PDU on 4-hour breach rate.

FIGURE 14 Impact of PDU implementation on weekly number of ED mental health attendances in SGUHFT. Note: the black vertical line represents implementation of the PDU. (Figure not reproduced here; see the original article.)

Pooled estimates of impact of psychiatric decision unit implementation

Table 15 shows the fixed and random effect pooled estimates for primary ITS outcomes concerning informal inpatient admission and ED mental health attendance activity. Significant heterogeneity in site outcomes were observed for all estimates except informal inpatient admission step change, which suggested a robust decrease (of 16.6%) in informal admission frequency following PDU implementation across participating sites. While fixed effects suggested that, overall, there was a significant decrease in informal admission frequency trend from pre to post PDU (by about 0.2%/week), reversing a steady weekly increase in trend prior to PDU implementation, after adjustment for random effects, the pre-to post-PDU change in weekly trend was not significant. The introduction of PDUs had no overall effect on level or trend in mental health presentations at ED. Although fixed-effects modelling suggested a highly significant weekly increase in ED attendances in the post-PDU period, this was not significant after adjustment for random effects.

Meta-analysis of secondary ITS outcomes indicated that (after adjustment for random effects where appropriate) PDU implementation had significant overall effects on formal inpatient admission percentage (step change increase by 7.3%), PLE frequency in individuals with recent episode activity (pre-to post-PDU trend decrease of 0.25%/week), proportion of ED mental health attendances with discharge to acute trust ward (step change increase of 3.2% points, pre-to post-PDU trend increase of 0.14% points/week) and length of mental health ED stay (pre-to post-PDU trend increase of 0.10%/week). Fixed- and random-effect pooled estimates for secondary ITS outcomes are detailed in Appendix 4, Tables 36–38.

Psychiatric decision unit and pathway reconfiguration

Key changes to the crisis care pathway (other than PDU introduction) within the duration of the study period, elicited through semistructured interviews with strategic managers and contact with trust staff in each site, are presented in (superimposed on) graphs showing ITS analyses of PDU implementation on primary outcomes in Appendix 4, Figures 53–56. Explanation of these changes to the crisis care pathway and a more detailed list including minor changes are provided for each site in Appendix 4, Tables 39–42.

Implementation of the PDU often occurred as part of or concurrently with reconfiguration or expansion of crisis care services at participating sites. The influence of each major service initiative (that occurred sufficiently distant in time from the study period start/end and from PDU implementation) on primary outcomes was (separately) examined in ITS analyses that included each in conjunction with PDU implementation (see Appendix 4, Tables 43–46 for parameter estimates and detailed commentary). These analyses tended to reaffirm the significant decrease in informal inpatient admissions following PDU implementation in BSMHFT, LPFT and SWLSTG. But they also suggested some earlier initiatives significantly affected short-term admission rates, such as the introduction of street triage services in BSMHFT (decrease of 20.5%) and the opening of a psychiatric intensive care unit in LPFT (increase of 34.7%). In addition, the introduction of some services post-PDU implementation were also potentially impactful, particularly in sites where significant long-term post-PDU decreases in admissions were observed (LPFT and SWLSTG). For example, there was an immediate decrease in informal observed admissions after the launch of a crisis vehicular response unit (15 months post PDU) in LPFT (by 40.1%) and long-term changes in trend (decreases) in weekly admission rates in SWLSTG following the introduction of crisis cafe (20 weeks post-PDU) and street triage services (30 weeks post-PDU).

The impact of additional crisis care pathway changes on ED mental health attendances was more mixed. A Secure Quality Involvement initiative specifically intended to reduce repeat ED mental health attendances in STHFT introduced at the start of the time series is likely relevant to the highly significant decreases in attendances observed prior to PDU implementation, although expansion of the liaison psychiatry service (step decrease of 26.3%) and closure of assertive outreach and intensive rehabilitation teams (increase of 1.0%/week) in this period also significantly influenced short- and long-term ED activity. Also, there were immediate decreases in ED mental health attendances in SGUHFT following introduction of a street triage service (by 16.7%/week) and subsequent development/expansion of the PDU service (by 26.6%/week). But changes in crisis care pathway appeared to have less impact in SWBHFT and ULHFT.