Cognitive failure (CF) is observed in delirium, dementia and amnestic disorder. Reported prevalence rates for CF/delirium in palliative care range from 14 - 44% and 28 - 52% respectively, and above 85% are delirious close to death. Unless terminal, deliria might be reversible. Successful treatment has consequently great impact on patient care and quality of life. Still delirium is reported overlooked in up to 67%. Identification of CF/delirium is therefore crucial. The clinical interview is the basis for identifying CF/delirium in the clinical setting. The interview should address conscious level, orientation, memory and attention. Duration is of paramount importance for distinguishing between delirium and dementia, and relatives/care-givers are therefore important informants. For research purposes the interview can be supplemented with a structured psychiatric interview like the SCID. Such interviews aim at establishing a psychiatric diagnosis (i.e. dementia, delirium or amnestic disorder). Self-report measures of CF such as the Cognitive Functioning Scale of the EORTC QLQ-C30 are of lesser value because these presuppose cognitive functioning at a relatively high level. Such measures are therefore better understood as measures of mental fatigue. They might be of relevance in measurement of subjectively experienced cognitive functioning as part of psychological distress or induced by medication such as opioids. Several instruments have been developed for assessment of cognitive failure and/or delirium. All are interview-based. Few are specifically developed for use in palliative care, and the need for palliative care specific instruments is questionable. However, just a few of the published instruments have been validated in palliative care. For example the most commonly used instrument for assessment of CF in palliative care, the Mini-Mental State Exam (the MMSE), has not been validated in this setting. While the MMSE measures CF, other instruments address specific symptoms associated with CF/ delirium. Knowledge about the content of the instruments is therefore highly recommended. The sensitivity and specificity across instruments varies and it is uncertain if there are any gains in using the instruments for screening.
Conclusions: Several instruments are available. They measure CF or specific symptoms associated with CF/delirium. Knowledge of the content of the measures is central. The instruments’ appropriateness in terms of diagnostic capabilities is uncertain. For ordinary clinical practice the clinical interview is the preferred method.