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?

Background

• 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

Design

• 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

Setting

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

Population

• 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)

Outcome

• 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

Strengths

• 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 clinicaltrials.gov

Weaknesses

• 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

• [article] 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’
• [Further reading] Increased mortality associated with weekend hospital admissions: a case for expanded seven-day services?
• [Further reading] Association between time of admission to the ICU and Mortality: A systematic review and Meta-analysis
• [Further reading] Increased mortality associated with after-hours and weekend admission to intensive care: A retrospective analysis
• [further reading] Weekends affect mortality risk and chance of discharge in critically ill patients: a retrospective study in the Austrian registry for intensive care
• [further reading] Nighttime Intensivist Staffing and Mortality among Critically Ill Patients

Metadata

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

Additional editing: Steve Mathieu