Chest
Volume 130, Issue 3, September 2006, Pages 869-878
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Recent Advances in Chest Medicine
Long-term Neurocognitive Function After Critical Illness

https://doi.org/10.1378/chest.130.3.869Get rights and content

Background

Until relatively recently, critical care practitioners have focused on the survival of their patients and not on long-term outcomes. The incidence of chronic neurocognitive dysfunction has been underestimated and underreported, and only recently has it been studied in critically ill patients. However, neurocognitive outcomes have been the subject of extensive investigation in other medical populations for many years.

Methods

Review of the current literature regarding long-term neurocognitive outcomes following critical illness.

Results

Data from studies to date indicate that critical illness can lead to significant neurocognitive impairments. The neurocognitive impairments persist for months and years, and may have important consequences for quality of life, the ability to return to work, overall functional ability, and substantial economic costs. The mechanisms of the neurocognitive impairments are not fully understood but likely include delirium, hypoxia, glucose dysregulation, metabolic derangements, inflammation, and the effects of sedatives and narcotics among other factors. The contributions of these factors may be particularly significant in patients with preexisting vulnerabilities for the development of cognitive impairments such as mild cognitive impairment, dementia, prior traumatic brain injury, or other comorbid disorders associated with neurocognitive impairments.

Conclusions

Current research indicates that neurocognitive sequelae following critical illness are common, may be permanent, and are associated with impairments in daily function, decreased quality of life, and an inability to return to work. Research needs to be done to better understand the prevalence, nature, risk factors, and nuances of the neurocognitive impairments observed in ICU survivors.

Section snippets

PREVALENCE AND NATURE OF CHRONIC NEUROCOGNITIVE IMPAIRMENTS

Medical and surgical management of critical illnesses can, and frequently does, result in de novo neurocognitive impairments. Research is limited regarding neurocognitive outcomes in survivors of critical illness; however, these patients are at risk for delirium (eg, acute cerebral dysfunction) during ICU treatment and chronic neurocognitive impairments.11, 12, 13, 14, 15 Early reports of chronic neurocognitive impairments after critical illness have been concerning, although additional

DURATION OF THE NEUROCOGNITIVE IMPAIRMENTS

Many critically ill patients have significant chronic neurocognitive impairments at 2 months,17 6 months,18, 24 9 months,21 1 year,16, 19, 23 2 years,28 and up to 6 years.20, 25 Neurocognitive impairments improve during the first 6 to 12 months post-hospital discharge. For example, 70% of ARDS survivors had neurocognitive impairments at hospital discharge, but only 45% had neurocognitive impairments at 1 year. There was no additional improvement in neurocognitive sequelae from the 1-year

REMOTE ASSESSMENT OF NEUROCOGNITIVE FUNCTION

A more complete understanding of the neurocognitive impairments following critical illness will require larger samples. Such studies may be hampered by the difficulties of performing in-person neurocognitive assessments in large multicenter studies or where face-to-face neurocognitive testing is impossible or impractical (such as in centers with a large geographic referral area). A 2004 study26 assessed neurocognitive function in ARDS survivors using questionnaires and tests administered over

Clinical Variables

A consistent finding across investigations is that no associations were found between some indicators of illness severity and the development of neurocognitive impairment or unfavorable neurocognitive outcomes. ICU length of stay, acute physiology and chronic health evaluation (APACHE) II scores, duration of mechanical ventilation, tidal volume, or number of days receiving sedative, narcotic, or paralytic medications were not associated with neurocognitive impairments in critically ill patients.

LACK OF RECOGNITION OF COGNITIVE IMPAIRMENTS

A recent study28 found that 42% of ARDS survivors underwent rehabilitation therapy, but most were not evaluated for neurocognitive impairments, with only 12% identified as having neurocognitive impairments by the clinical rehabilitation team. Neurocognitive impairments appear to be underrecognized by both ICU and rehabilitation providers. Studies have suggested that in non-ICU clinical settings many physicians fail to recognize (or assess) neurocognitive impairment in 35 to 90% of patients.38

CONSEQUENCES OF CHRONIC NEUROCOGNITIVE IMPAIRMENTS

The consequences of chronic neurocognitive impairments are far-reaching and typically contribute to a decreased ability to perform activities of daily living, decreased quality of life, increased medical costs, and the inability to return to work. Two years after hospital discharge, 34% of ARDS survivors were working or were full-time students, 34% were receiving disability payments that started after hospital discharge for ARDS, and 32% patients (20 of 62 patients) were not working or were

POTENTIAL MECHANISMS OF NEUROCOGNITIVE IMPAIRMENTS

There is probably not a single uniform cause of neurocognitive impairments, but rather a number of more or less significant factors that interact dynamically with premorbid variables and result in adverse outcomes (Figure 4). Data regarding the potential mechanisms of neurocognitive impairments are limited, but possible mechanisms may include hypoxemia,16 the use of sedatives or analgesics,51 hypotension,19 delirium,52 and hyperglycemia.18 The degree and duration of hypoxemia were modestly

CONCLUSIONS

The investigation of neurocognitive function after critical illness is in its infancy, with a small number of investigations in existence documenting both the presence of de novo neurocognitive impairment in a significant percentage of ICU survivors without preexisting deficits and the worsening of neurocognitive impairment in individuals who were previously impaired. It has been widely recognized that the physical consequences of critical illness are far-reaching and sometimes permanent,

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