Study assesses prevalence of delirium among survivors of cardiac arrest treated with hypothermia

A study in the American Journal of Critical Care (AJCC) found a remarkably high prevalence of delirium in a small cohort of critically ill patients treated with therapeutic hypothermia after cardiac arrest.

The research team conducted a retrospective review of the medical charts of 251 patients treated with therapeutic hypothermia after cardiac arrest from 2007 through 2014 in the cardiovascular intensive care unit (ICU) at Vanderbilt University Medical Center, Nashville, Tennessee. The analysis includes 107 patients who survived and awoke from coma. It excludes those who were persistently comatose or died before discharge from the ICU.

The results indicate all patients included in the study experienced at least one day of delirium between rewarming and subsequent discharge from the ICU.

Jeremy Pollock, MD, is lead author of the study, "Delirium in Survivors of Cardiac Arrest Treated With Mild Therapeutic Hypothermia," published in the July 2016 issue of AJCC. He is a fellow in the division of cardiovascular medicine at the University of Maryland Medical Center, Baltimore.

"The high prevalence of delirium in this population calls for a need to better understand the relationship between delirium and long-term outcomes in these patients," he said. "We need to improve the survival rate for patients who experience sudden cardiac arrest."

Mild therapeutic hypothermia is recommended for comatose patients resuscitated from cardiac arrest. It remains the standard of care after cardiac arrest, because it is associated with improvement in neurological outcomes after ventricular fibrillation and ventricular tachycardic arrest. However, outcomes remain poor, and identification of additional interventions and modifiable risk factors may lead to improvements in neurological outcomes.

The researchers examined risk factors both before and after resuscitation that they hypothesized could influence the duration of delirium. Among prehospital risk factors, they found age and longer times from initiation of CPR to return of spontaneous circulation were associated with increased duration of delirium.

Among risk factors after resuscitation, they found that higher total doses of propofol while comatose were protective against delirium in this cohort, and further study is needed to understand whether outcomes differ if delirium occurs with or without sedation.

The researchers caution that these findings are limited to this unique cohort and may not be generalizable to different populations. The degree of injury that cardiac arrest induced, the tremendous swings in metabolism from therapeutic hypothermia, and the large doses of psychoactive medications all most likely contributed to the higher prevalence.

The researchers call for further prospective research to understand the relationship between sedative and paralytic choice during therapeutic hypothermia and prevalence and duration of delirium, as well as the relationship between delirium and long-term outcomes in patients treated with therapeutic hypothermia after cardiac arrest.