Intensive Care Medicine

, Volume 33, Issue 6, pp 1007-1013

First online:

Subsyndromal delirium in the ICU: evidence for a disease spectrum

  • Sébastien OuimetAffiliated withIntensive Care Unit, Maisonneuve-Rosemont Hospital and Université de Montréal
  • , Richard RikerAffiliated withDivision of Pulmonary/Critical Care Medicine, Maine Medical Center
  • , Nicolas BergeonAffiliated withService of Consultation-Liaison Psychiatry, Centre Hospitalier del’Université de Montréal
  • , Mariève CossetteAffiliated withBiostatistics Service, Montreal Heart Institute Coordinating Center
  • , Brian KavanaghAffiliated withDepartments of Anesthesia and Critical Care Medicine, Hospital for Sick Children and University of Toronto
  • , Yoanna SkrobikAffiliated withIntensive Care Unit, Maisonneuve-Rosemont Hospital and Université de Montréal Email author 

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ICU delirium is common and adverse. The Intensive Care Delirium Screening Checklist (ICDSC) score ranges from 0 to 8, with a score of 4 or higher indicating clinical delirium. We investigated whether lower (subsyndromal) values affect outcome.


600 patients were evaluated with the ICDSC every 8 h.

Measurements and results

Of 558 assessed patients 537 noncomatose patients were divided into three groups: no delirium (score = 0; n = 169, 31.5%), subsyndromal delirium (score = 1–3; n = 179, 33.3%), and clinical delirium (score ≥ 4; n = 189, 35.2%). ICU mortality rates were 2.4%, 10.6%, and 15.9% in these three groups, respectively. Post-ICU mortality was significantly greater in the clinical delirium vs. no delirium groups (hazard ratio = 1.67) after adjusting for age, APACHE II score, and medication-induced coma. Relative ICU length of stay was: no delirium < subsyndromal delirium < clinical delirium and hospital LOS: no delirium < subsyndromal delirium ≈ clinical delirium. Patients with no delirium were more likely to be discharged home and less likely to need convalescence or long-term care than those with subsyndromal delirium or clinical delirium. ICDSC score increments higher than 4/8 were not associated with a change in mortality or LOS.


Clinical delirium is common, important and adverse in the critically ill. A graded diagnostic scale permits detection of a category of subsyndromal delirium which occurs in many ICU patients, and which is associated with adverse outcome.


Delirium Intensive care Screening Outcome Critical care Cognitive abnormalities