Abstract & Commentary

Can We Predict Long-Term Cognitive Impairment in Survivors of Critical Illness?

By Linda L. Chlan, RN, PhD, School of Nursing, University of Minnesota, is Associate Editor for Critical Care Alert.

Dr. Chlan reports that she receives grant/research support from the National Institutes of Health.

Synopsis: In survivors of critical illness with documented cognitive impairment at discharge, commonly used cognitive screening tests do not predict which of these patients will experience long-term cognitive impairment.

Source: Woon FL, et al. Predicting cognitive sequelae in survivors of critical illness with cognitive screening tests. Am J Respir Crit Care Med 2012; 186:333-340.

As more patients are surviving critical illness, there is documentation of serious cognitive, physical, and psychiatric consequences arising from lengthy ICU stays in these patients. Numerous studies have demonstrated new cognitive impairments in ICU survivors, yet there is no evidence available as to which patients are likely to experience long-term cognitive impairments after hospital discharge. The study by Woon and colleagues was conducted to address this knowledge gap. The researchers wanted to determine if commonly used cognitive screening tests administered at hospital discharge could be used to predict cognitive impairments, termed cognitive sequelae, 6 months later.

The baseline cognitive screening tests were the Mini-Mental State Examination (MMSE), which is the "gold standard" for cognitive status screening, and the Mini-Cog used to detect cognitive impairments; both were administered at hospital discharge. A battery of cognitive tests was administered 6 months after discharge from the hospital, including the Wide Range Achievement Test-3 Reading subtest (WRAT-3) and the Wechsler Abbreviated Scale of Intelligence (WASI). A number of neuropsychological tests were also administered 6 months after discharge to look for the presence of cognitive sequelae, including attention, upper extremity motor speed, language, memory-delayed recall, long-delay recall, mental processing speed, and executive function. Detailed information on this extensive battery of cognitive and neuropsychological tests can be found in the article by Woon et al.

Patients receiving mechanical ventilation for > 48 hours who were 18-85 years of age were recruited from the Shock Trauma ICU and Respiratory ICU at LDS Hospital and Intermountain Medical Center in Salt Lake City, Utah, from August 2007, through December 2008. Of the 319 patients who initially met the study inclusion criteria, only 70 (50% male) participated in the cognitive assessments at hospital discharge. Of these 70 participants evaluated at hospital discharge, 10 died between discharge and the 6-month follow-up period, three declined to participate, and four were lost to follow-up contact. A final sample of 53 participants completed the 6-month follow-up, with an average age of 54 years, mean hospital length of stay of 25 days, mean ICU length of stay of 13.3 days, and mean duration of mechanical ventilation of 8.8 days.

At hospital discharge, 39% of the participants were impaired on both the MMSE and the Mini-Cog; 64% were impaired on the MMSE only with 45% impaired only on the Mini-Cog. Perhaps not surprisingly, only 28% of the patients had normal scores on both cognitive screening tests. At 6 months post-hospital discharge, controlling for pre-ICU cognitive function, education, depression, and days of mechanical ventilation, the MMSE and Mini-Cog scores were not found to predict cognitive sequelae in this sample. However, a number of the measured cognitive sequelae were found in these ICU survivors at the 6-month follow-up including, most prominently, impaired memory (38%), executive dysfunction (36%), and slow upper extremity motor speed (26%). Of note, the researchers did not assess for the presence of delirium at any time in this study.

Commentary

The primary aim of the study by Woon and colleagues was to determine if the MMSE and the Mini-Cog could predict cognitive sequelae in survivors of prolonged critical illness. While the findings addressing the primary aim were not found to be statistically significant, the most clinically significant finding from this article is the marked cognitive sequelae in this sample of ICU survivors. Of note, this sample of study participants was relatively young (54 years of age) with impairments in memory and executive function 6 months after hospital discharge. These findings have important implications for quality-of-life outcomes in survivors of prolonged critical illness and their ability to return to work.

The small sample of only 53 participants out of an initial group of more than 300 patients limits the generalizability of these findings to ICU survivors in general. However, the marked cognitive impairments in these patients should give pause to all ICU clinicians when discussing post-ICU outcomes with patients and their family members. Surviving a prolonged critical illness may come with significant cognitive, physical, and psychiatric consequences that can directly impact quality of life.