Long-term cognitive impairment is a significant public health problem. In the October 3 issue of the New England Journal of Medicine, the BRAIN-ICU Investigators, led by Pratik Pandharipande, MD, conducted a multicenter, prospective cohort study to estimate the prevalence of long-term cognitive impairment after critical illness and to test the hypothesis that patients with a longer duration of delirium and a higher sedative and analgesic requirement have more severe cognitive impairment up to 1 year after hospital discharge.
Adults admitted to a medical or surgical ICU with respiratory failure, cardiogenic shock, or septic shock were included. While hospitalized, they were evaluated for delirium and level of consciousness daily with the use of the Confusion Assessment Method for the ICU (CAM-ICU) and the Richmond Agitation-Sedation Scale (RASS). Global cognition and executive functions were assessed three and 12 months after discharge with the use of the Repeatable Battery for the Assessment of Neuropsychological Status and the Trail Making Test, Part B. Multiple linear regression with adjustment for multiple variables was used to examine independent risk factors for global cognition scores and secondary outcomes.
Of the 821 patients enrolled, 6% had cognitive impairment at baseline, and 74% developed delirium during the hospital stay. At three months, 40% of the patients had global cognition scores that were approximately 1.5 standard deviations below the age-adjusted population mean and worse than scores observed in patients with moderate traumatic brain injury. Twenty-six percent of patients had scores 2 standard deviations below the population mean, which was similar to patients with mild Alzheimer disease. At 12 months, deficits of the same severity were also common. At both three and 12 months, a longer duration of delirium was independently associated with worse global cognition (P = 0.001 and P = 0.04, respectively) and worse executive function (P = 0.004 and P = 0.007, respectively). The use of sedatives or analgesics was not consistently associated with worse outcomes at 3 and 12 months after discharge.
The major findings from this study show that cognitive impairment after critical illness is common and persists for at least one year in some patients. This impairment is not seen only in aged patients or those with coexisting conditions at baseline. Limitations to this work include a diverse set of admission diagnoses, patients lost to follow-up or disenrolled before the 3- and 12-month assessments, and some missing data that required imputation techniques. The majority of study patients (>88%) were white, and the median level of education was 12 years. Hence, the results may not be externally generalizable across populations with higher or lower education levels or different racial or ethnic status. Patients were maintained on mechanical ventilation for a median of two to three days; it is possible that prolonged critical illness and longer duration of mechanical ventilation may cause even worse cognitive outcomes. Nearly three of four patients in the study had delirium. Delirium likely remains underdiagnosed in intensive care units, but when present, the longer the duration, the worse the impaired cognition.
This Concise Critical Appraisal is authored by Guirguiss Tadros, MD, fellow in Surgical Critical Care, University of Maryland R Adams Cowley Shock Trauma Center, Baltimore, Maryland.