Delirium is a frequent form of psychopathology in elderly hospitalized patients; it is a symptom of acute somatic illness. Serious conditions such as a heart attack may present in elderly patients with no symptoms other than delirium. The consequences of delirium include high morbidity and mortality, lengthened hospital stay, and nursing home placement . Caring for a delirious patient is experienced as burdensome by nurses. Early recognition of delirium symptoms enables the underlying cause to be diagnosed and treated and can prevent negative outcomes . The main symptoms of delirium are a disturbance of consciousness with reduced attention and a change in cognition or perceptual disturbances . Symptoms develop in hours to days and fluctuate over the course of the day. Owing to the fluctuating nature and different presentations of the condition, delirium is difficult to diagnose and is often missed.
Nurses have frequent round-the-clock contacts with patients and are in a strategic position to observe changes in behaviour [4, 5]. However, they are not well trained in recognizing delirium. In our experience, they observe behavioural changes in patients but often do not define them as symptoms of delirium. In VU university medical centre, a 733 bed university hospital, we therefore decided to introduce a standardised scale to enhance the recognition of delirium.
To implement delirium screening successfully, nurses need instruments that are based on observation and allow bedside use during regular care, repetitively and without respondent burden [6–8]. Two scales have been developed that meet these criteria: the NEECHAM Confusion Scale  and the Delirium Observation Screening (DOS) Scale . Both scales have been developed to rate nurses' observations during regular care and have been tested on several samples with good results.
The NEECHAM Confusion Scale  was developed to assess acute confusion on the basis of criteria identified by nurses as representing acute confusion. The instrument has been tested on several samples [7–9] and shows good internal consistency (0.85 – 0.90), inter-rater reliability (0.91 – 0.96) and test-retest reliability (0.98). Validity has been evaluated by calculating the correlation with the Mini Mental State Examination (MMSE) (0.50 – 0.87), nurses' reports of confusion (0.43 – 0.46) and patients' self-reports of confusion (0.40 – 0.44). The correlation with a DSM-III-R diagnosis ranged from -0.54 to -0.70. Construct validity has been tested by correlation with several measures of functional status (0.47 – 0.70). Analysis of variance showed two components explaining 72% of all variance.
The Delirium Observation Screening Scale  was developed on the basis of the DSM-IV criteria for delirium and tested for content validity by a group of experts in the field of delirium. In two prospective studies with high-risk groups of patients, the DOS Scale showed high internal consistency (0.93 – 0.96) [11, 12]. Predictive validity against the Diagnostic and Statistical Manual-IV diagnosis of delirium made by a geriatrician was good in both studies. Correlations of the DOS Scale with the MMSE were -0.66 and -0.79. Concurrent validity, as tested by comparison of the research nurse's ratings of the DOS Scale and the Confusion Assessment Method (CAM), was 0.63. Construct validity of the DOS has been tested against the Informant Questionnaire of Cognitive Decline in Elderly (IQCODE) (0.33 and 0.74) and the Barthel Index (-0.26 and -0.55). An algorithm of 13 items rated over 3 consecutive shifts has been developed. The sensitivity of this algorithm was 0.94, specificity 0.77 .
Both scales were developed for nurses without specific training in geriatric care. However, they have never been compared to each other in one study. This comparative study was designed in order to decide which instrument to implement in our hospital. The aim of the study was to test the discriminative value of each scale and to determine their ease of use in daily care.