 
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Journal of the New Zealand Medical Association,
11-September-2009, Vol 122 No 1302
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Emergency Department utilisation: a natural
experiment
Cecelia Rademeyer, Peter Jones, Stuart Dalziel, Garry
Clearwater, Bernard Foley, Mazin Ghafel
Overcrowding in Emergency Departments (EDs) has become an
international phenomenon1–5 and has been
hotly debated in the medical literature. Overcrowding has been associated with
increased morbidity and mortality, raising serious concerns about quality of
care.6–9 This problem has also attracted
media attention in New Zealand, especially for North Shore Hospital, with
newspaper reports of long waits for patients in
corridors.10–14
Causes identified internationally include a reduction in the
number of EDs and available ED beds, as well as an increase in patient
visits.15,16 Attempts to reduce overcrowding
have included a number of strategies from central government funding incentives,
addressing assessment and treatment times, to increasing ED beds. Despite
increase ED bed numbers being suggested as an answer to this problem, little
research has focused on the effect of increasing the number of available ED beds
within a geographic region on ED utilisation.
In February 2005 a new hospital-based ED was commissioned at
Waitakere Hospital (WH) in Henderson, West Auckland. Part of the rationale for
opening this new facility was the expectation that it would reduce attendances,
and thus overcrowding, in neighbouring EDs.
As the regional population is geographically well defined,
the opening of the new facility presented an opportunity to study the impact
that a new ED had on patient presentations to neighboring EDs.
BackgroundAuckland City is located in the top third of the North
Island of New Zealand and is bordered by two natural harbours, the Waitemata and
the Manukau. These harbours divide the city into northern and southern parts,
with only two highways and one rail link connecting them across a narrow
isthmus, 800m wide (Figure 1).
Figure 1. Auckland geography: the Auckland
isthmus and hospital locations
 NSH=North Shore Hospital, ACH=Auckland City Hospital,
SSH=Starship Children’s Hospital, WH=Waitemata Hospital, MMH=Middlemore
Hospital. Black Arrow=Isthmus.
The area had a population of 1,231,500 in the 2001 Census,
and 1,387,780 during the 2006 Census.17 At the
northern and southern boundaries of the Greater Auckland area the population
density is low and divided from the neighbouring areas (Northland and Waikato
respectively) by natural geographic barriers (Figure 2).
Figure 2. Auckland geography: District Health
Boards (DHBs)
 Source: Sector Accountability &
Funding Directorate, Ministry of Health.
Health services within Auckland are provided by three
District Health Boards (DHBs): Auckland District Health Board (ADHB) and
Waitemata District Health Board (WDHB) which respectively serve the central and
northern part of the city, and Counties Manukau District Health Board (CMDHB)
which serves the southern part (Table 1).
Table 1. Hospital-based services within the
Greater Auckland region
Prior to February 2005, the population north of Auckland
City was served by one ED at North Shore Hospital (NSH). In response to
projected population growth and overcrowding at NSH ED a new ED was commissioned
at Waitakere Hospital (WH). It was postulated prior to the opening of WH ED that
this new ED would result in a decrease in presentations at NSH and ADHB
hospitals (Auckland City Hospital (ACH) and Starship Children’s Hospital
(SSH)).
Ambulance patients from West Auckland would now be taken
directly to WH. Self-presenting patients were expected to present to WH rather
than NSH or ACH/SSH as this was closer. This study was designed to test that
hypothesis.
As Middlemore Hospital (MMH) in the south of the region is
geographically separated from the other hospitals (Figure 2) the opening of the
new ED was not expected to affect presentations to MMH ED. Furthermore, because
of its location at the northern boundary of its catchment area, CMDHB patients
usually present to the MMH ED rather than others north of the narrow isthmus.
MMH therefore served as a natural control for the study.
MethodsStudy design—A retrospective
analysis of all ED attendances obtained from the electronic databases of the EDs
within the Auckland region was undertaken over a 49-month period from February
2003 to February 2007. Clerical staff record patient attendance electronically
at the time of first presentation, to be used for funding and audit of hospital
performance. The data is believed to be accurate.
The study is an observation of an intervention (at time
point N), the opening of the new WH ED. Data obtained included all ED
attendances to the four existing EDs for two 12-month periods (Year N-1 and N-2)
prior to the opening of WH ED (N), and to all five hospitals for two 12-month
periods (N+1 and N+2) after its opening. Data are presented by hospital and by
DHB. See below.
The month of February 2005 was excluded from analysis
a priori as this was the month the new WH ED opened.
Statistics—The effect of the
opening of WH ED on ED presentations was explored using control charts (also
known as Shewhart charts or 'process-behaviour
charts').18 The control charts were generated
using SPSS v14 software (SPPS Inc, Chicago, USA). A control chart is a tool used
to study how a process changes over time. It helps distinguish between variation
in a process resulting from common causes (i.e. natural/non-significant
variation) and variation resulting from special causes (significant variation).
A special cause is anything which leads to an
observation beyond a control limit. A control chart presents a graphic display
of process stability or instability over time. Data are plotted in time order. A
control chart has a central line for the mean, an upper line for the upper
control limit and a lower line for the lower control limit. The control limits
are commonly set at three standard deviations (SD) from the mean (which
corresponds to a false alarm rate of 0.27%). By comparing the plotted data to
the mean and control lines conclusions can be drawn about whether the variation
in data, and hence the process, is within predictable limits or is
unpredictable, in other words affected by special causes of variation.
Special causes can be identified by the following
signs:
Control charts can also be used to see if an event
occurring at a given time point has a significant impact on the process. For our
study data ED attendance (the process) was analysed as monthly data points with
control lines determined at three standard deviations from the mean. Eight or
more data points in a row on one side of the mean line were considered to be
significant.
Population estimates for each DHB (as expected in June of
each year) for the years 1996 to 2010 were obtained from Statistics New
Zealand19 to see if
there were any major population shifts in individual DHB populations that might
explain changes in ED presentation numbers to the DHBs.
Results
The population in the region increased a total of 9.4% over
the study period (Table 2).
Table 2. Population per District Health
Board
Source: Statistics New
Zealand19. *Data for 2003, 2004, 2005 and 2007
is estimated. ADHB=Auckland District Health Board, WDHB=Waitemata District
Health Board, CMDHB=Counties Manukau District Health Board.
Yearly presentations to each hospital and DHB over the study
period are shown in Tables 3 and 4. There is a 74% increase in presentations to
WDHB, with only minor increases in the other DHBs. This increase is mainly due
to presentations to the new ED at WH.
Table 3. Presentations per study hospital over
the study period
ACH=Auckland City Hospital, SSH=Starship Hospital,
NSH=North Shore Hospital, WH=Waitakere Hospital, MMH=Middlemore Hospital.
Table 4. Presentations per DHB over study
period
ADHB=Auckland District Health Board, WDHB=Waitemata
District Health Board, CMDHB=Counties Manukau District Health Board.
The total population of the three DHBs is similar across the
region (Table 2). Although WDHB served the largest population, it received only
22% of regional ED presentations in the first two study years (Years N-2 and
N-1; (per capita ED attendance rate=0.09). However by the end of the study
period ED presentations were more evenly distributed and a closer match to the
population distribution, with per capita ED attendance rates of 0.20 at ADHB,
0.15 at WDHB and 0.17 at CMDHB.
Figure 3 is the control chart for ED
presentations to NSH over time
 NSH=North Shore Hospital
There is a grouping of points below the centre line for the
period before June 2004. The increase after this point is explained by the fact
that in June 2004 NSH started accepting Orthopaedic patients, coupled with a
severe winter. There is no evidence of special cause variation following
February 2005. Figure 4 shows the control chart for ED presentations to WDHB
over time.
There is evidence of special cause variation after February
2005, with an increase in attendances. The number of presentations to WDHB
increased 45% in the year after WH ED opened. Figure 5 shows the change in ED
presentations to ADHB over time.
Figure 4. Change in Emergency Department
presentations over time to Waitemata District Health Board
 WDHB = Waitemata District Health Board (North Shore and
Waitakere Hospitals).
Figure 5. Change in Emergency Department
presentations over time to Auckland District Health Board
 ADHB = Auckland District Health Board (Auckland City
and Starship Hospitals)
Two points below the lower control limit in February 2003
reflects a time prior to merger of Obstetric and Cardiothoracic services onto a
single hospital site in 2003. There is one point outside the upper control limit
in August 2004, reflecting a severe winter. This is a high point on all control
charts, reflecting a regional phenomenon. There is no evidence of special cause
variation following February 2005. Figure 6 shows the change in ED presentations
to CMDHB (MMH) over time (control group).
Figure 6. Change in ED presentations to the
control hospital over time
 CMDHB = Counties Manukau District Health Board,
MMH=Middlemore hospital
The chart displays a clear stable trend of increasing ED
presentations over the whole study period.
DiscussionRecently
Han20 reported that
ED expansion resulted in increased ED attendance rate and length of stay. It was
thought that opening a new hospital ED would help ease the load on neighbouring
hospitals in Auckland. However, the opening of the WH ED did not result in
reduced patient presentations to other EDs in the region. Instead, the numbers
increased in line with population growth (Figures 2 and 4) for both nearby and
distant hospitals (Figure 5). In contrast to this there was a marked increase in
ED presentations to WDHB, the area in which WH is situated, disproportionate to
population growth (45% in the first year and 74% over the first 2 years after
the opening of the new ED).
The effect of increasing hospital beds has been known for
sometime. In 1961 Roemer et al published a landmark
study21 which found
that increasing hospital bed availability was responsible for an increase in bed
utilisation and length of stay in a community previously thought to be
adequately served. Roemer suggested that doctors were the main drivers for the
increased use of hospital beds as more beds became available. Our study is the
first to report the effect of building a new ED on the patient attendances to
neighbouring EDs. The results of this study suggest that patients may directly
increase utilisation of a service, independent of the influence of doctors: the
increased ED utilisation at WDHB was mainly from lower-acuity
self-presentations. (This aspect is subject of a separate paper in publication).
A number of possibilities may explain our study findings.
Firstly, the increase in numbers of patients seen at WDHB following the opening
of the WH ED may reflect redistribution from the primary health care sector in
that area. This behaviour may be motivated by cost: in New Zealand ED care is
free while there is a variable part charge for primary care; or the perception
that presentation to a hospital ED allows greater access to specialist services.
We sought, but were unable to obtain information concerning
after-hours primary care presentations to the after-hours primary care centre
near the new facility. It is relevant to note that EDs see only a small
proportion of all primary (self-presenting) attendances in a community. The
attendance rate in general practice averages 4 visits per capita per
annum,22 whereas the average ED attendance rate
(in this study) is less than 0.2 visits per capita per annum.
A relatively small redistribution of primary care visits to
ED would barely register in all General Practice attendances but could have a
significant impact on ED attendances. In this study, the per capita ED
attendance rate at WDHB increased from a baseline of 0.09 visits per annum in
2003, to 0.15 visits per annum in 2007: this would barely register within the
margin of error for all primary care attendances over the same period.
An alternative explanation is that the need for secondary
emergency medical care for the population that lived closest to WH was not being
addressed by the available EDs prior to the opening of WH ED. There is some
evidence that this may have occurred in that the proportion of total ED
presentations that have occurred in the regional DHBs following the opening of
the new ED now more accurately reflects the distribution of the population in
the region.
It is likely that the increase in total presentations within
the WDHB, without a reduction in presentations to the nearby DHBs, reflects a
combination of these possibilities. This finding has considerable implications
for funding and resource allocation in the future.
As a retrospective observational study, our data may be
subject to information bias. However as all EDs in the region use a national
electronic database to establish a given individual’s unique hospital
number, this is unlikely. The data extracted did not include patient
demographics, address, presenting complaint, length of stay or final diagnosis
and disposition, which may have informed the debate regarding the
appropriateness of given presentations for primary care services.
Ideally, control charts would have been created for more
than 2 years before the opening of WH ED in order to identify long-term trends
in attendance rate. However in 2001 NSH underwent a major change in their
recordkeeping system and it is not possible to accurately compare ED data before
and after this change. No change in record keeping occurred in the three DHBs
during the study timeframe. Therefore we do not believe the results can be
explained by changes in data collection.
Given the large numbers involved in this study, any
differences in numbers attending would be likely to reach statistical
significance if subjected to traditional statistical tests of significance. We
believe that in this situation, use of control charts is more appropriate to
detect clinically important differences in the process of patient attendance
across the region.
The control chart method determines whether there has been
change at a given time-point not explained by natural variation or chance alone.
However, it does not determine why that change has occurred. It is possible that
the increase in ED presentations to the WDHB area at February 2005 is due to a
factor other than the opening of the WH ED. As there were no similar sharp
increases in presentations to either the adjacent Auckland, or geographically
distinct CMDHBs, we believe that there was no change in regional disease
morbidity to account for the increase in presentations.
During the study period there was also no change in
provision of primary care facilities in the area. Information about attendances
to General Practitioners may help explain where the additional patient visits
were created from, however we were unable to access this information.
ConclusionsThe opening of WH ED had no effect on the number of
presentations to the other hospitals in the region. However it appears to have
resulted in a marked increase of presentations to the new facility, thus
increasing the total numbers of ED patients seen within the Auckland region.
Conflict of interest: None known.
Author information: Cecilia Rademeyer,
Emergency Medicine Registrar, Department of Emergency Medicine, Auckland City
Hospital, Auckland; Peter Jones, Director of Emergency Medicine Research,
Specialist Emergency Physician, Department of Emergency Medicine, Auckland City
Hospital, Auckland; Stuart Dalziel, Specialist Paediatric Emergency
Medicine Physician, Children’s Emergency Department, Starship
Children’s Hospital, Auckland; Garry Clearwater, Specialist Emergency
Physician, Department of Emergency Medicine, North Shore Hospital, Auckland;
Bernard Foley, Specialist Emergency Physician, Department of Emergency Medicine,
Auckland City Hospital, Auckland; Mazin Ghafel, Public Health Physician/Analyst,
Funding and Planning, Auckland District Health Board, Auckland
Correspondence: Peter Jones, Department of
Emergency Medicine, Auckland City Hospital, Private Bag 92024, Auckland Mail
Centre, Auckland 1142, New Zealand. Fax: +64 (0)9 6309799 (int) 4999; email: peterj@adhb.govt.nz
References:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| | Current
issue | Search journal |
Archived issues | Classifieds
| Hotline (free ads) Subscribe | Contribute | Advertise | Contact Us | Copyright | Other Journals |
|