Epidemiology and clinical trials require valid, repeatable definitions that ideally dichotomise patients into having, or not having, a clinical condition. • Some conditions are clearly dichotomous, such as pregnancy; others such as
hypertension or
obesity rely on defining a threshold on an objective scale. • Defining
delirium and "adequate" sedation and
analgesia in the intensive care unit is more difficult, as there is no universally agreed scale that quantifies the relative importance of various diagnostic features, distinguishes features merely observed from those actively sought, quantifies severity or fluctuation over time, or accounts for the variable approaches of clinicians and the effects of assessment environment and pharmacological treatment. Definitions of
delirium and adequate sedation and
analgesia therefore vary by assessment method and context, making studies using different methods and personnel not necessarily comparable. • Although there is no simple
solution, we suggest better awareness of these problems will be helpful. Further, we propose a simplified categorisation to facilitate clinical communication and treatment in the ICU.