by Nancy Humphrey
More than 5 million patients are admitted annually to intensive care units in the United States, with more than 1.1 million of them suffering from acute respiratory failure requiring mechanical ventilation.
More than 50-75% of those surviving these admissions have substantial newly acquired disabilities, including long-term cognitive impairment similar to Alzheimer’s disease and related dementias that can persist from months to years after discharge from the ICU. For more than two decades, researchers in Vanderbilt University Medical Center’s Critical Illness, Brain Dysfunction and Survivorship center have been studying the long-term effects of ICU patients on ventilators and the debilitating effects of delirium on this group of patients.
A recent systematic review by Vanderbilt University Medical Center researchers, published in Critical Care Explorations, has taken a close look at the cognitive instruments used in long-term outcome studies of survivors of adult critical illness and how those test scores are interpreted.
The study concluded that there is no consistent way of reporting these outcomes, and that the reporting of neuropsychological instruments and scores should be standardized.
Since test scores may be associated with demographic factors, they are typically adjusted using four demographic variables: age, education, gender and race.
“There are many manuals which are used to adjust scores based on age and education, which is reasonable for cognitive outcomes, but they are also adjusted for race and/or ethnicity,” said Rameela Raman, PhD, associate professor of Biostatistics, Health Policy, Psychiatry and Behavioral Sciences, and Nursing and first author of the study, along with James Jackson, PsyD, the study’s senior author. “But this can create problems of equity because some people may not get the services they need, or some people might be receiving more treatment than they should be getting.”
Understanding the use of norms in cognitive testing is particularly important in studies of long-term cognition in ICU survivors because patients are typically assessed, and results are reported for a large battery of neurocognitive tests. Interpreting the scores can become challenging when some of the tests are normed and some are not.
The review of about 5,000 abstracts and 400 research papers, funded by a research grant from the Vanderbilt Center for Health Services Research, looked at whether the measures were reported using demographic norms, specifically race norms.
“We recommend that in the future investigators report the raw score, the norm score, which variables were used for norming and which battery that particular instrument belonged to,” Raman said.
“We found that less than half of the studies measuring cognitive outcomes in ICU survivors reported the use of norming characteristics,” she said. “There is substantial heterogeneity in how studies reported the use of cognitive instruments, and hence, the prevalence of the use of patient norms may be underestimated,” she said. “Because it’s not clear whether some of these papers are using raw scores or they’re normed….it’s very hard to figure out if that’s a natural population variability or if it’s because they’re adjusting the scores.”
Raman said researchers should critically evaluate the algorithms they are using because it’s not a one-size-fits-all approach.
“I feel like it really impacts the way we’re able to compare different populations and make inferences as well. In many cases, it’s like comparing apples to oranges because there’s no standard way of reporting these outcomes,” Raman said. “This is the beginning of a discussion, but there is a critical need to have the reporting of neuropsychological instruments and subsequent scores be standardized.”
