Understanding Cognitive Outcome Trajectories After Critical Illness.

1164 www.ccmjournal. org August 2019 • Volume 47 • Number 8 Cognitive impairments following critical illness were first described 2 decades ago (1). Since that time there has been a substantial increase in the number of cognitive outcome studies (2–6). Numerous studies have documented that the cognitive impairments after critical illness are new or worsening of pre-illness cognitive impairment (3, 7), cognitive impairments persist months to years after hospital discharge, and occur in a variety of cognitive domains including attention, memory, language, and executive function, to name a few (2–6). Cognitive impairments range from mild to severe and are associated with new or worsening functional disability after critical illness (8). A study in 510 ICU survivors at 3-month follow-up found 40% of patients had cognitive scores that were more severe than cognitive impairments in patients with moderate traumatic brain injury and 26% cognitive impairments was similar to that of individuals with mild dementia (6). Although the prevalence, duration and severity of cognitive impairments after critical illness is well described, data regarding cognitive outcome subtypes, predictors/risk factors of cognitive impairments and cognitive trajectories are limited. Cognitive impairments in conjunction with physical and mental health (depression, anxiety, and posttraumatic stress disorder) make up the cluster of outcomes known as postintensive care syndrome (PICS) (9). Studies that assess all three areas of PICS (physical, mental health, and cognitive function) have found that some patients have impairments in only one area (i.e., mental health) whereas others can have impairments in two or all three areas (10, 11) suggesting that there are different clusters or subtypes of post-ICU outcomes. Recent data from a national multicenter prospective study of acute respiratory distress syndrome survivors found physical and mental health outcomes are associated and form four unique subtypes (mildly impaired physical and mental health, moderately impaired physical and mental health, severely impaired physical health and moderated impaired mental health, and severely impaired physical and mental health); in contrast cognitive impairments were not associated with physical and mental health outcomes and form a unique outcome subtype (12). Supporting data comes from a Canadian study that found physical outcomes did not predict cognitive impairments (13). These data suggest that cognitive outcomes appear to be unique and are not associated with physical and mental health outcomes suggesting there may be distinct etiology(s), mechanisms, and risk factors. Further interventions to prevent or ameliorate cognitive impairments may be different than for interventions for physical and mental health, although this remains to be studied. There is limited data regarding the trajectories of cognitive impairments after critical illness. A study by Schulte et al (14) that assessed the association between critical illness and cognitive trajectories in a population of older adults published in this issue of Critical Care Medicine adds important new data to our knowledge. Schulte et al (14) assessed the association between ICU admission and trajectory of cognitive impairment in patients who were admitted to the ICU compared with patients admitted to the hospital. Data from a population-based study of adults age 50 and over, the Mayo Clinic Study of Aging (MCSA) were analyzed for the study by Schulte et al (14). Patients in the study received a baseline evaluation at study enrollment and then they were evaluated every 15 to 30 months thereafter. Of the 3,673 patients who had at least one follow-up visit 372 were admitted to the ICU, of whom 87 had a diagnosis of dementia at study enrollment. Baseline global cognitive z-scores declined over time; the slope of the decline was greater (more negative) in the patients treated in the ICU compared with patients who did not require ICU admission. In additional global cognitive decline, decline also occurred in the cognitive domains of memory, attention, and visuospatial function. There was no difference in the global cognitive scores for patients with baseline mild cognitive impairment compared with individuals who were cognitively not impaired. Nor was there an interaction between of age at enrollment and global cognitive scores, indicating that global cognitive decline occurred regardless of patient age. Decline in global cognitive scores and specific cognitive domains (e.g., memory) did not differ by the type of admission (trauma, medical, or surgical). In addition, patients treated in the ICU who had delirium had greater decline in the domains of memory and language but no decline for global z scores, visuospatial, or attention/executive function domains compared with ICU patients without delirium (14). 0090-3493