Clinical phenotypes of delirium during critical illness and severity of subsequent long-term cognitive impairment: a prospective cohort study

Abstract

Background: Delirium during critical illness results from numerous insults, which might be interconnected and yet individually contribute to long-term cognitive impairment. We sought to describe the prevalence and duration of clinical phenotypes of delirium (ie, phenotypes defined by clinical risk factors) and to understand associations between these clinical phenotypes and severity of subsequent long-term cognitive impairment.

Methods: In this multicentre, prospective cohort study, we included adult (≥18 years) medical or surgical ICU patients with respiratory failure, shock, or both as part of two parallel studies: the Bringing to Light the Risk Factors and Incidence of Neuropsychological Dysfunction in ICU Survivors (BRAIN-ICU) study, and the Delirium and Dementia in Veterans Surviving ICU Care (MIND-ICU) study. We assessed patients at least once a day for delirium using the Confusion Assessment Method-ICU and identified a priori-defined, non-mutually exclusive phenotypes of delirium per the presence of hypoxia, sepsis, sedative exposure, or metabolic (eg, renal or hepatic) dysfunction. We considered delirium in the absence of hypoxia, sepsis, sedation, and metabolic dysfunction to be unclassified. 3 and 12 months after discharge, we assessed cognition with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). We used multiple linear regression to separately analyse associations between the duration of each phenotype of delirium and RBANS global cognition scores at 3-month and 12-month follow-up, adjusting for potential confounders.

Findings: Between March 14, 2007, and May 27, 2010, 1048 participants were enrolled, eight of whom could not be analysed. Of 1040 participants, 708 survived to 3 months of follow-up and 628 to 12 months. Delirium was common, affecting 740 (71%) of 1040 participants at some point during the study and occurring on 4187 (31%) of all 13 434 participant-days. A single delirium phenotype was present on only 1355 (32%) of all 4187 participant-delirium days, whereas two or more phenotypes were present during 2832 (68%) delirium days. Sedative-associated delirium was most common (present during 2634 [63%] delirium days), and a longer duration of sedative-associated delirium predicted a worse RBANS global cognition score 12 months later, after adjusting for covariates (difference in score comparing 3 days vs 0 days: -4·03, 95% CI -7·80 to -0·26). Similarly, longer durations of hypoxic delirium (-3·76, 95% CI -7·16 to -0·37), septic delirium (-3·67, -7·13 to -0·22), and unclassified delirium (-4·70, -7·16 to -2·25) also predicted worse cognitive function at 12 months, whereas duration of metabolic delirium did not (1·14, -0·12 to 3·01).

Interpretation: Our findings suggest that clinicians should consider sedative-associated, hypoxic, and septic delirium, which often co-occur, as distinct indicators of acute brain injury and seek to identify all potential risk factors that may impact on long-term cognitive impairment, especially those that are iatrogenic and potentially modifiable such as sedation.

Funding: National Institutes of Health and the Department of Veterans Affairs.

Figure 1:. Prevalence of delirium phenotypes according to study day

Each area plot shows (on the y-axis) the percentage of study participants in the hospital who had any delirium, a single delirium phenotype, or a combination of multiple delirium phenotypes according to study day (shown on the x-axis). The grey shading indicates the overall percentage of participants with delirium on each study day. The red lines and shaded areas represent the number of phenotypes of delirium present, with darker reds representing the presence of more phenotypes of delirium. The lightest red regions, therefore, show the percentage of participants with a given single phenotype. H=hypoxic. M=metabolic. Sed=sedative. Sep=septic.

Figure 2:. Associations between duration of delirium phenotypes and global cognition scores at 3- and 12-month follow-up

Each line graph shows the association between the duration of a delirium phenotype (on the x-axis) and global cognitive performance on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) at 3 months (red lines, with the 95% CI represented by red shading) and 12 months (blue lines, with the 95% CI represented by blue shading) after hospital discharge.