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Weekend admissions as an independent predictor of mortality: an analysis of Scottish hospital admissions
  1. Adam E Handel1,2,
  2. Sunil V Patel3,4,
  3. Andrew Skingsley3,5,
  4. Katrina Bramley3,6,
  5. Roma Sobieski3,
  6. Sreeram V Ramagopalan1,2,3,7
  1. 1Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
  2. 2Nuffield Department of Clinical Neurosciences (Clinical Neurology), University of Oxford, Oxford, UK
  3. 3Department of Epidemiology, London School of Hygiene and Tropical Medicine, London, UK
  4. 4Department of Surgery, London Health Sciences Centre, London, Canada
  5. 5Department of Epidemiology and Public Health, Imperial College Medical School. London, UK
  6. 6Department of Anaesthesia, Glasgow Royal Infirmary, Glasgow, UK
  7. 7Blizard Institute, Queen Mary University of London, Barts and The London School of Medicine and Dentistry, London, UK
  1. Correspondence to Dr Sunil V Patel; Sunil.Patel{at}londonhospitals.ca, Dr Sreeram V Ramagopalan; s.ramagopalan{at}qmul.ac.uk

Abstract

Objectives Weekend admissions have been shown to be associated with an increased risk of mortality compared with weekday admissions for many diagnoses. We analysed emergency department admissions within the Scottish National Health Service to investigate whether mortality is increased in case of weekend emergency department admissions.

Design A cohort study.

Setting Scotland National Health Service (NHS) emergency departments.

Participants 5 271 327 emergency department admissions between 1999 and 2009. We included all patients admitted via emergency departments recorded in the Scottish Morbidity Records (SMR01) in NHS, Scotland for whom complete demographic data were available.

Primary outcome measures Death as recorded by the General Register Office (GRO).

Results There was a significantly increased probability of death associated with a weekend emergency admission compared with admission on a weekday (unadjusted OR 1.27, 95% CI 1.26 to 1.28, p<0.0001; adjusted for year of admission, gender, age, deprivation quintile and number of comorbidities OR 1.42, 95% CI 1.40 to 1.43, p<0.0001).

Conclusions Despite a general reduction in mortality over the last 11 years, there is still a significant excess mortality associated with weekend emergency admissions. Further research should be undertaken to identify the precise mechanisms underlying this effect so that measures can be put in place to reduce patient mortality.

  • Accident & Emergency Medicine

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Article summary

Article focus

  • Weekend admissions have been associated with excess mortality.

  • This article addresses whether this excess mortality is seen in emergency admissions from National Health Service, Scotland between 1999 and 2009.

Key messages

  • The risk of death associated with weekend emergency admissions is significantly higher than that of weekday emergency admissions.

  • This risk persists even when adjusted for year of admission, gender, age, deprivation quintile and number of comorbidities.

Strengths and limitations of this study

  • This study uses a large, nationally registered cohort of admissions obtained over a long time period.

  • Although able to adjust for many confounding variables, it was not possible to adjust for the admitting diagnosis or severity of presenting a complaint.

Introduction

Service provision within National Health Service (NHS) hospitals has traditionally been organised around a fundamental division between weekdays and weekends. However, mortality data drawn from many different sources indicate that weekend admission to hospital is associated with an increased risk of death.1–5 This has prompted a shift in health policies within the UK towards consideration of a 7-day working week within the NHS.

The evidence illustrating an adverse effect of weekend admission on death rates is strong and growing constantly. A recent study using the NHS database of all NHS hospital admissions within England showed a significantly increased risk of death for patients admitted at the weekend, even when adjusted for multiple potential confounders.5 Similar analyses of emergency admissions within multiple hospitals in England and Spain have shown a similar detrimental effect of weekend admissions on survival.3 ,4 Increased mortality with weekend admissions is consistent across multiple pathologies suggesting a systematic failure of care.6–9 One study from Canada suggested an increased rate of mortality for some causes of admission (ruptured aortic aneurysm, pulmonary embolism and acute epiglottitis) but not others (acute myocardial infarction, hip fracture and intracranial haemorrhage),1 although subsequent studies from the USA suggest that myocardial infarction presenting at weekends is associated with an increased mortality.6 A similar effect was observed for acute kidney injury and stroke.8 ,9

This effect spans multiple different age groups (perinatal mortality is increased at weekends, although not when adjusted for birth weight) and clinical areas (intensive care admissions at the weekend are associated with an increased mortality).10–12 Particularly influential to policies has been the report by Dr Foster on an increased hospital mortality in the UK at weekends, which has been linked to a reduced cover by senior doctors at weekends.13 ,14

In this study, we aimed to investigate emergency admissions within NHS, Scotland to establish if a similar effect of weekend admissions on mortality occurred in this region.

Methods

Scottish admissions data

The Scottish Morbidity Records (SMR01) database of Scottish inpatient/daycase admissions and General Register Office (GRO) death records for Scotland were accessed on 26 February 2011 for emergency department admissions. The basic unit of analysis was the continuous spell of treatment (CIS). These were grouped according to the admission date, gender, age, deprivation quintile (based on Scottish Index of Multiple Deprivation 2009 V.2 Scotland level population-weighted quintile, where 1 is the most deprived and 5, the least) and number of recorded comorbidities. Probability matching methods were used to link together separate SMR01 hospital episodes for each patient, thereby creating ‘linked’ patient histories. Within these patient histories, SMR01 episodes are grouped according to whether they form part of a continuous spell of treatment (whether or not this involves transfer between hospitals or even Health Boards). Mortality during admission was derived from the GRO death record linked to the SMR.

Ethics statement

Anonymised data were used and we therefore followed the ethical principles of existing UK data protection legislation and guidance, including two National Statistics Protocols on data access and confidentiality, and data matching. Thus specific ethical approval was not required for this study according to the guidelines at http://www.nhsnss.org/pages/corporate/privacy_advisory_committee.php, which permitted the release of the data used in this study.

Statistical analysis

Data were analysed in STATA V.12.0 (StataCorp LP, College Station, Texas, USA). Multiple logistic regression was used for calculating ORs, 95% CIs and p values for individual factors. We interpreted p values of <0.05 as nominally significant. χ2 Tests were used for testing for significance of trends within factors. Only records without missing data were included in the multiple logistic regression model.

Results

Scottish emergency department admissions

There were 5 343 906 admissions to emergency departments in Scotland between 1999 and 2009, of which 5 271 327 (98.6%) had admission date, gender, age, deprivation quintile and number of comorbidities recorded. Of all admissions, 270 463(5.03%) ended in death. This was very similar to the proportion of admissions for which all data were recorded that ended in death (266 119(5.05%)). The majority of deaths for which all data were recorded occurred during weekdays (191 929, 4.77% of weekday admissions) rather than on weekends (74 190, 5.77% of weekend admissions). The subsequent analysis applies only to those admissions with complete records of the above data. About 4 025 845 (76.4%) of these were on weekdays and 1 245 482 (23.6%) on weekends. There were few admissions during weekends than expected from a random distribution (23.6% observed vs 28.6% expected, p<0.0001). Admissions and death rates broken down by each category are shown in table 1.

Table 1

Number and percentages of emergency department admissions by category

Mortality for weekend admissions compared with weekday admissions

The mortality for weekend admissions was found to be higher than that for weekday admissions (5.96% vs 4.77%, unadjusted OR 1.27, 95% CI 1.26 to 1.28, p<0.0001). The effect of weekend admissions was still statistically significant when adjusted for admission year, gender, age group, deprivation quintile and number of comorbidities (adjusted OR 1.42, 95% CI 1.40 to 1.43, p<0.0001). All of the potential confounders included in the logistic regression model were independently statistically associated with the probability of death for emergency admissions as shown in tables 1 and 2. Notably, the number of comorbidities shows an inverse trend on mortality that would not be expected a priori. Further, mortality after being admitted to a hospital has been declining over time (2009 mortality was 25% less than that in 1999, p<0.0001). However, the effect of admission at weekends on mortality remained much the same throughout the 11-year period studied (table 3).

Table 2

Results of a logistic regression analysis of emergency department admissions and mortality

Table 3

Odds of mortality of those admitted during weekends, compared with those admitted during weekdays, stratified by year

Causes of death

Our study was not designed to investigate cause-specific aspects of mortality data. Table 4 shows the top 50 causes of death for weekend and weekday admissions. The patterns of mortality seem to appear relatively similar between weekends and weekdays. Further research would be needed to gather diagnosis-specific admission data to analyse mortality further.

Table 4

Top 50 causes of death

Discussion

Our study shows that the excess of admissions ending in deaths at weekends compared with those during weekdays seen elsewhere were also found in Scotland and, in fact, appear to be of a larger magnitude than the effects reported elsewhere (table 5). Despite a reduction in mortality over the course of the study, after adjusting for this and multiple other potential confounding variables, the weekend effect on mortality remains.

Table 5

Previous studies of emergency admissions and mortality for weekdays and weekends admissions

The strength of our study is that it analyses data from a large number of emergency admissions drawn from over a relatively long period of 11 years. There are a number of limitations. We lack data on cause and severity of admissions. The analysis relies on the accuracy of data input by clinicians and clerical staff involved in individual admissions and thus unlikely to be entirely accurate. Furthermore, since the regression analysis only included records with complete data recorded, there is a possibility of introducing systematic bias into our study.

Several possible explanations may clarify the seemingly counter-intuitive finding that the number of comorbidities is inversely associated with mortality. It is possible that timing of utilisation of emergency department admissions differs by number of comorbidities or that this merely reflects a survivor effect, whereby those that live longer accumulate more comorbid diagnoses.

The cause for this increased mortality is an area of considerable debate. Many of the studies reporting excess deaths at weekends adjusted for many of the obvious potential confounders (age, comorbidities, deprivation, etc). However, interestingly the effect appears to be persistent even when more careful analyses adjusting for specific confounders that would a priori be hypothesised to be adversely affected at weekends, such as time to angiography for myocardial infarction and time to oesophagogastroduodenoscopy in peptic ulcer-related upper gastrointestinal haemorrhage.6 ,7 ,15 However, in a recent study from Australia it was noted that, of the conditions they assessed (myocardial infarction, chronic obstructive pulmonary disease, intracranial haemorrhage and acute hip fracture), there was observed an association of weekend admissions with mortality in myocardial infarction, the condition in which a delay to instrumentation is likely to have the largest effect on outcome.16 Certainly, institutional standards appear to be able to mitigate the excess weekend mortality, at least in case of ischaemic strokes, wherein no increase in mortality for weekend admissions has been observed in ‘comprehensive stroke centres’ within the USA, but is still seen in less-specialist centres.9 It may also be that emergency departments see a different, more unwell population of patients at weekends, since, in one study which used a biochemical measure of severity, adjustment for this variable rendered the weekend effect insignificant.17 It is possible that a confounding variable associated with severity, for which we were unable to control, underlies the weekend effect. This could mean that the effect we observe is actually due to admissions over the weekend comprising a more unwell population of patients, who would suffer a higher rate of mortality regardless of factors that may apply exclusively to the weekend.

It is clearly critical to understand the precise cause of this excess mortality before measures can be put in place to mitigate the effect of weekend admissions on survival, particularly given the potentially huge costs involved in upgrading weekend services. Resources and manpower in the hospital will clearly play a huge part in this, however, the importance of reduced primary care support at weekends in the community should not be forgotten, since early identification of unwell patients is likely to improve later outcomes and out-of-hours primary care has been shown to alter the profile of emergency department admissions.18 ,19 Further work should focus on understanding the precise mechanism behind the increased mortality observed for weekend admissions so that effective measures can be implemented to combat this. Ideally, this would entail ascertaining diagnosis and severity-specific weekend mortality by region and level of service infrastructure, incorporating broad aspects of prebased care and hospital-based care.

Acknowledgments

We are grateful to NHS, Scotland for providing us with data and to colleagues for many useful and informative conversations.

References

View Abstract

Related Data

Footnotes

  • Contributors AEH and SVR conceived the study idea. SVP analysed the data. AEH, SVP, AS, KB, RS and SVR wrote the paper.

  • Funding This work was funded by the Wellcome Trust (Grant Number 075491/Z/04). The funder had no role in data analysis or deciding to submit this manuscript for publication.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer-reviewed.

  • Data sharing statement Extra data can be accessed via the Dryad data repository at http://datadryad.org/with the DOI:10.5061/dryad.rm857.

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