The brain after critical illness: effect of illness and aging on cognitive function.

Large numbers of patients who survive critical illness are left with significant new cognitive impairments that are often severe and remain years after hospital discharge. In the previous issue of Critical Care, Guerra and colleagues assessed risk factors for the development of dementia after an intensive care unit (ICU) admission in a sample of older beneficiaries of Medicare. Older age was strongly associated with a diagnosis of dementia. The relationship between older age and development of dementia after critical illness has not previously been reported. After adjustment for known dementia risk factors, the multivariable analysis found that factors associated with the critical illness were associated with an increased risk of dementia. This study has several limitations - including use of ICD-9-CM codes that identified primarily neurodegenerative types of dementia, the lack of a control group, and a high mortality rate during the first 6 months after hospital discharge - which the authors acknowledge. An important additional limitation of the study by Guerra and colleagues and all previous post-ICU cognitive outcome studies is the inability to determine what role, if any, cognitive impairments that existed before the critical illness contribute to the diagnosis of new post-ICU dementia and whether such cognitive impairments are stable over time or are progressive like those observed in neurodegenerative diseases. Research is needed to answer questions regarding mechanisms of injury, medical and personal risk factors, and importantly the effect of interventions administered either during or after ICU treatment that may prevent or ameliorate such impairments.