Delirium Mediates Incidence of Hospital-Associated Disability Among Older Adults

Abstract

Objective: To examine whether delirium predicts occurrence of hospital-associated disability (HAD), or functional decline after admission, among hospitalized older adults.

Design: Retrospective cross-sectional study.

Setting and participants: General inpatient (non-ICU) units of a large regional Southeastern US academic medical center, involving 33,111 older adults ≥65 years of age admitted from January 1, 2015, to December 31, 2019.

Methods: Delirium was defined as a score ≥2 on the Nursing Delirium Screening Scale (NuDESC) during hospital admission. HAD was defined as a decline on the Katz Activities of Daily Living (ADL) scale from hospital admission to discharge. Generalized linear mixed models were used to examine the association between delirium and HAD, adjusting for covariates and repeated observations with multiple admissions. We performed multivariate and mediation analyses to examine strength and direction of association between delirium and HAD.

Results: One-fifth (21.6%) of older adults developed HAD during hospitalization and experienced higher delirium rates compared to those not developing HAD (24.3% vs 14.3%, P < .001). Age, presence of delirium, Elixhauser Comorbidity Score, admission cognitive status, admission ADL function, and length of stay were associated (all P < .001) with incident HAD. Mediational analyses found 46.7% of the effect of dementia and 16.7% of the effect of comorbidity was due to delirium (P < .001).

Conclusions and implications: Delirium significantly increased the likelihood of HAD within a multivariate predictor model that included comorbidity, demographics, and length of stay. For dementia and comorbidity, mediation analysis showed a significant portion of their effect attributable to delirium. Overall, these findings suggest that reducing delirium rates may diminish HAD rates.

Keywords: Delirium; activities of daily living; cognition; disability; functional impairment; hospitalization.

Figure 1.. Mediation Analysis.

The total effect, indicated by the path c, is the overall effect of the predictor (age, dementia, comorbidity, functional status, cognitive impairment, or length of stay) on the outcome (risk of hospital-associated disability or HAD). This total effect is broken down into the average causal mediation effect (ACME), indicated by the path ab, which is the effect of the predictor on the mediator (risk of delirium), which in turn increases the risk of HAD; and the average direct effect (ADE), indicated by the path $c^{\prime }$, which is the effect of the predictor to increase the risk of HAD that is independent of its effects to increase the risk of delirium. The average proportion mediated is the ratio $\frac{ab}{c}$, which corresponds to the reduction in the outcome (HAD) that could be expected by reducing the mediator (rates of delirium). For logistic models used in our analyses, the estimates ab, c, and $c^{\prime }$ correspond to the percentage increase in the rates of HAD.

Figure 2.. Flow Diagram for Participant Selection.

Figure 3.. Mediation Results with Age as a Mediator.

The total effect, indicated by the path c, is the overall effect of age on risk of hospital-associated disability or HAD. Individuals in the 85+ year old group showed increased risk of HAD of 0.157 (95% CI 0.130, 0.180) or 15.7% compared to the 65–74 year old group. The average direct effect (ADE), indicated by the path c’, is the effect of age to increase the risk of HAD that does not occur by age increasing the risk of delirium. The 85+ year old group showed a direct increased risk of HAD of 0.149 (95% CI 0.124, 0.180) or 14.9% relative to the 65–74 year old group. The average causal mediation effect (ACME), indicated by the path ab, is the effect of age to increase the risk of delirium, with delirium then increasing the risk of HAD. The 85+ yar old group showed an indirect increased risk of HAD of 0.007 (95% CI 0.005, 0.010) or 0.7% through increased risk of delirium relative to the 65–74 year old group; this indirect effect accounts for 4.4% (95% CI 2.9%, 6.0%) of the risk of HAD due to age in the 85+ year old group.