Clinical paperValidity of the IQCODE-CA: An informant questionnaire on cognitive decline modified for a cardiac arrest population☆
Introduction
Cognitive disability is common among out-of-hospital cardiac arrest (OHCA) survivors and may affect their quality-of-life and participation in society [1], [2]. The increasing focus on outcome beyond survival [3] emphasizes the need for high quality, relevant and acceptable screening to identify cognitive decline. Cognitive disability can be assessed in several ways; through performance-based measures, clinician-reports, observer-reports, and patient-reports. However, the commonly used clinician-report Cerebral Performance Category (CPC) does not differentiate higher cerebral function among survivors [4], and underestimates the number of survivors with cognitive impairment [5]. In contrast, observer-reports are standardized instruments completed by other informants than patients or health care professionals, such as family members. Yet no observer-reported outcome measure has been developed specifically for cardiac arrest (CA).
The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) is a 26-item observer-reported outcome screening measure on dementia, with high reliability and good predictive validity [6]. These properties are important for acceptable diagnostic accuracy, which is required for a screening measure [7]. The IQCODE provides an estimate of decline in everyday cognitive function over a 10-year period. In the large multi-center Target Temperature Management (TTM) trial [8], a slightly modified version called the IQCODE-CA was used. Informants were requested to compare current cognitive function with pre-CA cognitive function, rather than with cognitive function ten years ago. Although previous studies have used other time frames, no clear evidence of diverging validity has been observed [9]. Using a previously established cut-off value (3.19) for the IQCODE to identify mild cognitive impairment (MCI) in the TTM-trial, the IQCODE-CA indicated a cognitive decline in 62% (302 of 491 survivors) [10]. However, the psychometric properties of the IQCODE-CA may not be the same as those of the original version. The best cut-off values to indicate cognitive decline may have changed due to the modified timeframe.
The aim of the present study was therefore to evaluate the modified IQCODE-CA, providing guidance for score interpretation and cut-off scores for the identification of decline in cognitive function related to the CA. We also wanted to explore the possible validity and reliability of a shortened version of the IQCODE-CA.
Section snippets
Study population
Unconscious patients ≥18 years of age with OHCA of a presumed cardiac origin were randomized at hospital arrival to target temperature management at 33 °C or 36 °C as previously reported in the TTM-trial [8], [11]. Survivors with completed IQCODE-CA [9] participating in an extended follow-up with additional cognitive tests [12] were included in the current study.
Procedure
Surviving participants [11] and informants, defined as relatives or close friends, were invited to a face-to-face interview at 180 ± 14
Results
Out of 287 OHCA survivors that participated in the follow-up of the extended cognitive substudy of the TTM-trial, 17 patients lacked IQCODE-CA and one had incomplete data on the IQCODE-CA (Fig. 1). One additional survivor was excluded as an outlier due to highly unlikely inconsistent scores. Clinical and demographic characteristics of the 268 remaining survivors are shown in Table 1. No significant differences were found between the excluded and included survivors in CPC scores and results on
Discussion
This study provides initial evidence of the data quality, structural and construct validity and reliability of a modified observer-reported measure of cognitive decline in CA survivors. The expected hypotheses were mostly accepted, as the IQCODE-CA was a unidimensional measure of global cognitive decline, had negligible associations with gender and education, and had a small to moderate positive association with measures of anxiety and depression.
Our hypothesis regarding an alpha value above
Conclusions
The IQCODE-CA has acceptable psychometric properties in an OHCA population and shows results similar to earlier studies of the original version. A lower AUC ratio than desired and probable item redundancy indicates that the instrument should be supplemented by performance-based measures, to improve the overall scope of assessment. Yet, the IQCODE-CA identified a large number of patients with possible cognitive problems, making it an important screening tool for cognitive decline in post-CA
Conflicts of interest
The authors declare that they have no actual or potential conflicts of interest with this work.
Acknowledgements
The Royal Swedish Academy of Sciences, The Swedish Heart and Lung Association, The Skane University Hospital Foundations, The Gyllenstierna-Krapperup Foundation, Academy of Caring Sciences at Skane University Hospital, The Swedish National Health System (ALF), The County Council of Skane, The Swedish Society of Medicine, The Koch Foundation, The Swedish Heart-Lung Foundation, AFA Insurance Foundation, The Hans-Gabriel and Alice Trolle-Wachtmeister Foundation for Medical Research, The Segerfalk
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at DOI:10.1016/j.resuscitation.2017.06.012.