Comparison of two methods for diagnosing delirium conducted in a mixed medical ICU and the concordance between two independent nurse assessors

Introduction

Delirium in ICU patients increases time on mechanical ventilation, is an independent risk factor for death and can cause cognitive impairment in survivors [1, 2]. The two most commonly used validated assessment methods for diagnosing delirium in intensive care are the Confusion Assessment Method for ICU (CAM) and the Intensive Care Delirium Checklist Score (ISDCS) [3]. We wished to determine the prevalence of delirium in our unit, whether there was a difference in results between these methods of assessment and whether good agreement could be achieved between two trained assessors.

Methods

We performed a prospective prevalence study in a single tertiary ICU. Patients were assessed between days 3 and 10 of their stay and tested provided their Richmond Agitation Sedation Score (RASS) was ≥-3 [1]. Each patient was independently assessed by the two trained assessors with the CAM and ISDCS, with randomisation of both the order of interview and the score used. Both sets of assessments were carried out within an hour of each other. Exclusions included readmissions, those who did not speak English, the deaf and registered psychiatric patients. The CAM was completed by the assessors and the ISDCS required observational answers from the bedside nurse.

Results

We performed 104 assessments (208 tests) on 52 patients. Mean (SD) age, APACHE II and total SOFA on the day of admission were 67.4 (14.0), 14.0 (5.3) and 5.7 (2.7), respectively. Delirium was found in 37.5% of patients using the CAM, but only 14.4% using ISDCS. Inter-rater agreement for CAM and ISDCS was 86.5% (κ 71.4%, SE 13.8%, P < 0.001) and 94.2% (κ 76.7%, SE 13.8%, P < 0.0001), respectively. There was significant underscoring of the RASS by the bedside nurses. When the trained assessors found a difference, it was always lower than the score documented by the bedside nurse.

Conclusions

There was good inter-rater agreement in the diagnosis of delirium between the two trained assessors, but the prevalence found was lower than previously reported [1] and varied considerably with the method used. The difference in results between the two scores may be due to a lack of discernment on the part of the bedside nurse of the ISDCS assessment process.