Long-term cognitive impairment and delirium in intensive care: A prospective cohort study

Abstract

Background

Whilst there is a growing body of research exploring the effect of delirium in intensive care unit (ICU) patients, the relationship between patient delirium and long-term cognitive impairment has not been investigated in settings where low rates of delirium have been reported.

Objectives

To assess the association between the incidence of delirium, duration of mechanical ventilation and long term cognitive impairment in general ICU patients.

Methods

Prospective cohort study conducted in a tertiary level ICU in Queensland, Australia. Adult medical and surgical ICU patients receiving ≥12 h mechanical ventilation were assessed for delirium on at least one day. Cognitive impairment was assessed at three and/or six-months using the: Repeatable Battery for the Assessment of Neuropsychological Status (RBANS); Trail Making Test (TMT) Part A and B; and Mini-Mental State Examination (MMSE).

Results

Of 148 enrollees, 91 (61%) completed assessment at three and/or six months. Incidence of delirium was 19%, with 41% cognitively impaired at three months and 24% remaining impaired at six months. Delirium was associated with impaired cognition at six-months: mean TMT Part A scores (information processing speed) were 7.86 s longer than those with no delirium (p = 0.03), and mean TMT Part B scores (executive functioning) 24.0 s longer (p = 0.04).

Conclusions

ICU delirium was positively associated with impaired information processing speed and executive functioning at six-months post-discharge for this cohort. Testing for cognitive impairment with RBANS and TMT should be considered due to its greater sensitivity in comparison to the MMSE.

Introduction

Delirium is a common neuropsychiatric syndrome that, although occurring in a range of healthcare settings, is particularly prevalent in hospitalised intensive care unit (ICU) patients. However, the incidence of ICU delirium varies widely worldwide—23–84% in North America[1], [2], [3], [4]; 15%–39% in Europe[5], [6]; 63% in Asia⁶; and 12%–45% in Australia.[6], [7] Reasons for these disparities include differences in the severity of illness of ICU patients between countries,³ methodological differences in research, the fluctuating nature of delirium and the inability of clinicians to detect delirium.⁸ Models of care differ in relation to sedation and mobilisation practices which affect rates of delirium in ICU patients.¹

Delirium in the ICU patient has been associated with various risk factors including patient age⁶; excessive alcohol consumption⁶; psychoactive medications including benzodiazepines and opioids⁹; mechanical ventilation¹⁰; coma; infection; metabolic acidosis and severity of illness.⁶ Adverse patient outcomes, both during hospitalisation and in the longer-term, post-discharge are also reported.[11], [12], [13], [14], [15], [16], [17], [18] These include prolonged mechanical ventilation¹⁵; increased ICU and hospital length of stay (LOS)¹⁵; increased risk of in-hospital falls¹⁶; increased risk of post-traumatic stress symptoms¹²; reduced quality of life post-discharge¹¹; increased risk of newly acquired functional disability in activities of daily living post-discharge²; and increased mortality rates.¹¹ In addition, patients are also at an increased risk of cognitive impairments months to years after ICU.¹⁹ Whilst improvements in cognitive function typically occur in the first year post ICU discharge,²⁰ between a quarter and half of ICU survivors report persistent impairment at one,[3], [4] two,²¹ and six years.²² Both longer duration of delirium[4], [5] and, more recently, greater severity of delirium,²³ have been identified as risk factors of cognitive impairment. Analgesics and sedative medications have also been posited as possible mechanisms through which both delirium and cognitive impairment develops,¹⁹ although findings to date remain mixed.[4], [24]

Whilst there is a growing body of research exploring the effect of delirium in ICU patients, the relationship between patient delirium and cognitive impairment has limited reports of investigation in settings where low rates of delirium have been reported.[6], [11], [17], [18] Consequently, the current study sought to explore the association between the incidence of delirium, duration of mechanical ventilation and patients’ cognition at three and six-months post ICU discharge. To aid international comparison, the study design was based on that conducted in the USA by Girard et al.,³ which was the first prospective cohort study to identify delirium as a predictor of long-term cognitive impairment at three and 12-months post-discharge All risk factors, covariates and outcomes were determined a priori and based on Girard et al.’s work.³ However, limitations of Girard et al.’s study included the exclusion of surgical patients, and the study being nested within a sedation and weaning protocol clinical trial³ which may have had some inadvertent impact on the results.