Association between day and time of admission to critical care and acute hospital outcome for unplanned admissions to adult general critical care units: cohort study exploring the ‘weekend effect’

Arulkumaran N, Harrison DA, Brett S. Br. J.Anaesth. (2016) doi: 10.1093/bja/aew398 First published online: December 7, 2016

Clinical Question

  • In patients who are unplanned admissions to critical care, does the day and time of admission to critical care influence acute hospital mortality?


  • Critically ill patients may present at any time of day, thus critical care unit staffing levels and resources should be adequate throughout a 24 h period, weekends, and holidays
  • It is imperative to ascertain whether out-of-hours services are adequate to cover emergency care without any adverse impact on outcome for patients


  • Retrospective cohort study
  • Data collected from UK Intensive Care National Audit and Research Centre (ICNARC) Case Mix Programme (CMP) database – a mandatory national audit collecting data on admissions and outcomes in all critical care units in the UK
  • Specialist units (neuro, cardiac) and standalone HDUs excluded
  • Each day divided into “routine hours” (0800-1759) and “out of hours” (1800-0759)
  • Any missing physiological data presumed normal
  • Potential confounders identified a priori and adjusted for in analysis:
    • Age
    • Severe conditions in past medical history
    • Prior functional dependency
    • Number of days from hospital admission to critical care admission
    • location before admission
    • CPR in 24 hours prior to critical care admission
    • Primary reason of admission to critical care
    • Acute severity of illness score (ICNARC and APACHE scores used)
  • Statistical Analysis:
  • 3 multilevel logistic regression models used:
    • Unadjusted with single covariant of day/time of admission
    • Adjusted model adjusting for key potential confounders:
    • Adjusted model including delay/no delay covariate


  • 216 General/mixed Intensive Care Units in the UK that submitted data for the ICNARC CMP
  • April 1 2013-March 31st 2015


  • Inclusions:
    • Age >16
    • Unplanned ICU admission
  • Exclusions:
    • Planned ICU admission (including post theatre, transfers and repatriation)
    • Readmissions – only the first episode was counted
    • Organ donation
    • Missing data (primary outcome or key confounders)
  • 300,469 admission screened, 195,428 included in final analysis
  • Baseline characteristics:
    • mean age of patients admitted was 60 yr
    • mean APACHE II score of 17
    • Approximately one-quarter of patients had some degree of prior dependency
    • Overall, 4% of patients received in-hospital CPR during the 24 h before admission and a further 4% had out-of-hospital CPR
    • The greatest proportion of patients was admitted with a primary respiratory pathology (25.5% of all admissions)
    • No significant differences between the two cohorts seen in any of the major criteria, including age, severity of illness, and co-morbidities

Weekend days cohort

  • Day of admission analysis: Patients admitted on Saturday or Sunday
  • Time of admission analysis: During routine working hours (0800-1759) and out of (1800 0759)

Week days cohort

  • Day of admission analysis: Patients admitted on Monday, Tuesday, Wednesday, Thursday or Friday
  • Time of admission analysis: During routine working hours (0800-1759) and out of (1800 0759)


  • Primary outcome:
    • Total ICU mortality: 18.8%
    • Total hospital mortality: 26.6%
    • Using Monday as reference day, no significant difference seen between odds of admission out of hours or at a weekend in adjusted analysis (P value =0.61)
  • Secondary outcome:
    • 8,295 (4.2%) patients experienced a delay (documented decision to admit to time of admission) of at least 1 hour prior to admission to ICU. 2,097 (1.1%) had delay >4hrs
      • Both groups associated with an increased risk of death (OR 1.08 for < 4hrs, 1.17 for >4 hrs, P=0.04)
      • Adjusting to account for delay did not change lack of effect of day/time of admission

Authors’ Conclusions

  • After risk adjustment using detailed clinical data, there was no difference in acute hospital mortality for unplanned admissions to ICU between weekdays and weekends, or daytime and nighttime
  • A small proportion of patients experienced delays in admission to ICU and this was associated with an increased risk of death


  • Important clinical question
  • Large detailed database with very little missing data
  • Multi centre
  • Detailed risk adjusted analysis performed, with confounders identified a priori
  • Secondary analysis also an important clinical question
  • Registered on


  • Study design can only demonstrate association, and not causation
  • Significant heterogeneity exists between size and staffing of units in the ICNARC CMP – this would affect the internal validity of the data
  • Does “delayed admission” include transport time, or time spent in radiology?
  • “Delayed admission” is a complex entity which may or may not include delays in treatment – this could not be commented on in the study
  • It may be the effect of delayed admission was actually a delay in getting essential treatments (antibiotics, cardiovascular resuscitation etc)
  • Limited external validity – this study may not be relevant to non-UK institutions, with different staffing and bed availability

The Bottom Line

  • This article did not show an association between date and time of admission and increased mortality, but showed an association between delayed admission to ICU and increased mortality
  • I will try to ensure that patients who require critical care receive the appropriate treatment in the appropriate place as soon as possible

External Links


Summary author: Segun Olusanya
Summary date: 7th February 2018
Peer-review editor: Adrian Wong

Additional editing: Steve Mathieu

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