New research suggests that older adults with preoperative pain and depressive symptoms have a higher risk of delirium following surgery.

Researchers from Harvard Medical School found that both pain and depression are independent and interactive risk factors for delirium, suggesting a cumulative effect.

Individuals with delirium experience a sharp decline in attention and mental function. Older adults are especially susceptible to delirium following surgery, occurring in up to 51 percent of surgical patients 65 and older. Moreover, depression is a common risk factor for delirium, with medical evidence showing a two- to three-fold increase in risk.

"Understanding the impact of preoperative pain and depression on risk of delirium in older surgical patients is important," Cyrus Kosar, lead author of the study, said in a statement. "By exploring the interaction between pain, depression, and delirium we may uncover potential targets for intervention."

For the study, researchers collected and analyzed data from more than 400 non-dementia patients, 70 years of age or older, who were scheduled for orthopedic surgery between June 2010 and August 2013. Patients self-reported current pain along with the average and worst pain for the previous seven days. Prior to surgery depressive symptoms were assessed using the geriatric depression scale and chart review. Post-surgical delirium was measured by the confusion assessment method and chart review.

They found that 23 percent of patient patients showed signs of delirium, which occurred much more frequently in patients with depressive symptoms prior to surgery than in those without depression. Researchers found preoperative pain was linked to increased risk of delirium across all pain measures.

Further analyses found that patients with depressive symptoms had a 21 percent increased risk of delirium associated with a one-point difference in the worst pain score, while patients without depressive symptoms demonstrated only a fraction of the risk (3 percent), indicating a significant interaction between pain and depressive symptoms.

"Our study demonstrates that the combination of higher symptoms of pain and depression increases delirium risk in older adults," Sharon Inouye, an author of the study and principal investigator of the Successful Aging After Elective Surgery (SAGES) study from which the study participants were drawn, said in a statement. "Doctors considering surgery for older patients should be aware of the delirium risk and potential contributions of pain and depressive symptoms in their preoperative evaluations."

The findings are detailed in The Lancet Psychiatry journal.