title: The impact of pre-admission morbidity level on 3-year mortality after intensive care: a Danish cohort study.
abstract: BACKGROUND
  Chronic diseases are common among intensive care unit (ICU) patients and may worsen their prognosis. We examined the prevalence and impact of pre-admission/index morbidity among ICU patients compared with a general population cohort.
  
  
  METHODS
  Our study encompassed all 28,172 adult patients admitted to ICUs in northern Denmark in 2005-2007 and 281,671 age- and sex-matched individuals from the general population. We used a nationwide hospital registry to obtain a 5-year history of 19 chronic diseases and computed Charlson Comorbidity Index (CCI) for each study participant and grouped them into low (CCI=0), moderate (CCI=1-2), and high (CCI=3+) morbidity levels. We computed mortality and mortality rate ratios (MRRs) adjusted for confounders, and compared the mortality between ICU patients and the general population cohort.
  
  
  RESULTS
  Low, moderate, and high pre-admission morbidity levels were present in 51.5%, 34.1%, and 14.4% of ICU patients, respectively. In these groups, 30-day mortality was 10.8%, 18.4%, and 26.7%, respectively. Three-year mortality was 21.3%, 43.1%, and 63.2%, respectively. The adjusted 30-day MRR was 1.30 [95% confidence intervals (CI): 1.21-1.39] and 1.86 (95% CI: 1.71-2.01) for ICU patients with moderate and high morbidity levels, both compared with a low morbidity level. The general population had a lower morbidity level and mortality at all morbidity levels throughout the study period. Interaction between ICU admission and high morbidity level added 5.1% to the mortality during the second and third year of follow-up.
  
  
  CONCLUSIONS
  A high pre-admission morbidity level was frequent among ICU patients and associated with a worsened prognosis. Morbidity had more impact on mortality among ICU patients compared with a general population cohort.
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Denmark. cc@dce.au.dk
authors.forename: C F
authors.initials: CF
authors.lastname: Christiansen
authors.forename: S
authors.initials: S
authors.lastname: Christensen
authors.forename: M B
authors.initials: MB
authors.lastname: Johansen
authors.forename: K M
authors.initials: KM
authors.lastname: Larsen
authors.forename: E
authors.initials: E
authors.lastname: Tønnesen
authors.forename: H T
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015897:Comorbidity; D016001:Confidence Intervals; D003422:Critical Care / Q000706:statistics & numerical data*; D016638:Critical Illness / Q000401:mortality; D016208:Databases, Factual; D003718:Denmark / Q000453:epidemiology; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D009026:Mortality / Q000639:trends*; D010343:Patient Admission; D011153:Population; D016016:Proportional Hazards Models; D012042:Registries; D015203:Reproducibility of Results; D012737:Sex Factors; D016019:Survival Analysis; D055815:Young Adult