title: Hospital mortality is associated with ICU admission time.
abstract: BACKGROUND
  Previous studies have shown that patients admitted to the intensive care unit (ICU) after "office hours" are more likely to die. However these results have been challenged by numerous other studies. We therefore analysed this possible relationship between ICU admission time and in-hospital mortality in The Netherlands.
  
  
  METHODS
  This article relates time of ICU admission to hospital mortality for all patients who were included in the Dutch national ICU registry (National Intensive Care Evaluation, NICE) from 2002 to 2008. We defined office hours as 08:00-22:00 hours during weekdays and 09:00-18:00 hours during weekend days. The weekend was defined as from Saturday 00:00 hours until Sunday 24:00 hours. We corrected hospital mortality for illness severity at admission using Acute Physiology and Chronic Health Evaluation II (APACHE II) score, reason for admission, admission type, age and gender.
  
  
  RESULTS
  A total of 149,894 patients were included in this analysis. The relative risk (RR) for mortality outside office hours was 1.059 (1.031-1.088). Mortality varied with time but was consistently higher than expected during "off hours" and lower during office hours. There was no significant difference in mortality between different weekdays of Monday to Thursday, but mortality increased slightly on Friday (RR 1.046; 1.001-1.092). During the weekend the RR was 1.103 (1.071-1.136) in comparison with the rest of the week.
  
  
  CONCLUSIONS
  Hospital mortality in The Netherlands appears to be increased outside office hours and during the weekends, even when corrected for illness severity at admission. However, incomplete adjustment for certain confounders might still play an important role. Further research is needed to fully explain this difference.
authors.affiliation: Department of Intensive Care Medicine, University Medical Center Utrecht, Location AZU, Room F06.135, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
authors.forename: Hans A J M
authors.initials: HAJM
authors.lastname: Kuijsten
authors.affiliation: Department of Medical Informatics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Brinkman
authors.affiliation: Department of Intensive Care, Reinier de Graaf Groep, Delft, The Netherlands.
authors.forename: Iwan A
authors.initials: IA
authors.lastname: Meynaar
authors.affiliation: Department of Intensive Care, Gelre Hospital Apeldoorn and Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Spronk
authors.affiliation: Department of Intensive Care Medicine, University Medical Center Utrecht, Location AZU, Room F06.135, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
authors.forename: Johan I
authors.initials: JI
authors.lastname: van der Spoel
authors.affiliation: Department of Intensive Care, Onze Lieve Vrouwe Gasthuis (OLVG), Amsterdam, The Netherlands.
authors.forename: Rob J
authors.initials: RJ
authors.lastname: Bosman
authors.affiliation: Department of Medical Informatics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Nicolette F
authors.initials: NF
authors.lastname: de Keizer
authors.affiliation: Department of Medical Informatics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Ameen
authors.initials: A
authors.lastname: Abu-Hanna
authors.affiliation: Department of Intensive Care Medicine, University Medical Center Utrecht, Location AZU, Room F06.135, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands. D.W.deLange@umcutrecht.nl.
authors.forename: Dylan W
authors.initials: DW
authors.lastname: de Lange
mesh_terms: D018806:APACHE; D000328:Adult; D000368:Aged; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010343:Patient Admission / Q000706:statistics & numerical data*; D012042:Registries