Patients who had been depressed prior to their hospitalization, and those who were in the ICU longer, were more likely to experience symptoms. Other apparent factors associated with a greater likelihood of a PTSD experience were those given high doses of opiates and those who developed bloodstream infections.
In fact, Bienvenu says, sepsis, or infections of the bloodstream, may play an important role in causing chemical confusion in the brain, perhaps in the amygdala, an area "important for fear conditioning," he says.
Infection may lead to an inflammation cascade that breaks down the blood brain barrier, and produces a bolus of noradrenaline. This somehow may allow traumatic memories of the hospital experience to be implanted, yet distorted, and that is what is recalled in subsequent delusions of what actually took place.
"Everyone remembers where they were on 9/11," Bienvenu explains. "We have a tendency to remember things that were emotionally arousing. These patients were on the verge of death, by definition, so a lot of experiences would be remembered vividly" except for the chemical reactions underway.