The inflammatory immune response that develops when the body tries to protect itself from harmful stimuli plays a role in the onset of delirium, according to US researchers.
A study of post-surgical patients has shown that elevated levels of inflammatory cytokines are strongly associated with the condition that affects many older people while in hospital.
“Understanding the role that inflammation plays in the onset of delirium can help us identify patients who may be at highest risk of developing this condition”
The new study found older patients with delirium had significantly elevated levels of the inflammatory marker interleukin-6 (IL-6) two days after surgery.
The study authors, from the Beth Israel Deaconess Medical Center in Boston, also identified elevated levels of interleukin 2 (IL-2) in delirious patients.
They said their findings may help clinicians identify patients at greatest risk of developing delirium and aid in the treatment of the condition, which occurs in two-thirds of older hospital patients and is also linked to the subsequent development of dementia.
Study co-author Professor Edward Marcantonio said: “With strong evidence for the involvement of IL-6 and evidence for the involvement of IL-2 in patients with delirium, it appears that inflammation is indeed a basic mechanism underlying this condition.
“Anything that causes tissue injury – including infection or illness as well as surgery – can activate various immune cells and cause inflammation,” he said. “Delirium may be an inflammatory response gone awry.”
The researchers examined data on 566 non-cardiac surgical patients over the age of 70, comparing those that developed delirium and those that did not.
“The results showed that levels of IL-6 were significantly elevated in the delirium patients two days after surgery”
They measured cytokines in blood samples taken prior to surgery to establish a baseline figure. Additional measurements were then taken at three separate time points – immediately following surgery, two days after surgery while the patient was still in hospital, and one month post-surgery.
Study co-author Dr Sarinnapha Vasunilashorn said: “The results showed that levels of IL-6 were significantly elevated in the delirium patients two days after surgery.
“The magnitude of difference in levels of IL-6 between delirious and non-delirious patients was about 10 times the upper limit for normal levels in older adults,” she said.
Moderate evidence for IL-2 was also reported, with delirious patients found to have higher levels at all four time points relative to non-delirious patients.
Dr Vasunilashorn noted that most previous research on inflammation and delirium had involved information at a single point in time. “Our collection of blood at four separate points gives us a more complete picture,” she said.
Dr Marcantonio added: “Delirium is the most common complication among hospitalised elders. Once widely assumed to be a short-term, transient condition, there is now evidence that delirium and its effects can last long after patients have left the hospital.
“Understanding the role that inflammation plays in the onset of delirium can help us identify patients who may be at highest risk of developing this condition, and take steps to reduce their risk. It can also help design new interventions to prevent or treat delirium,” he said.
The study findings have been published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences.