Effect of preoperative pain and depressive symptoms on the risk of postoperative delirium: a prospective cohort study

Summary

Background

Preoperative pain and depression predispose patients to delirium. We investigated whether pain and depressive symptoms interact to increase the risk of delirium.

Methods

We enrolled 459 people without dementia, who were aged 70 years or older and were scheduled for elective orthopaedic surgery between June, 2010, and August, 2013. At baseline, participants reported their current pain and the average and worst pain in the previous 7 days, on a scale of 0–10. Depressive symptoms before surgery were assessed with the 15-item geriatric depression scale and chart. Delirium after surgery was assessed with the confusion assessment method and chart. We used multivariable analysis to assess the relation between preoperative pain and postoperative delirium stratified by the presence of depressive symptoms.

Findings

Delirium was reported in 106 (23%) of patients, and was significantly more frequent in those with depressive symptoms at baseline than in those without (relative risk [RR] 1·6, 95% CI 1·2–2·3). Preoperative pain was associated with an increased adjusted risk of delirium across all pain measures (RR 1·07–1·08 per 1-point increase in pain). In stratified analyses, patients with depressive symptoms had a 21% increased risk of delirium for each 1-point increase in worst pain score, which indicated a significant interaction (p_interaction=0·049). Similarly, a 13% increased risk of delirium was seen per 1-point increase in average pain score, but the interaction was not significant.

Interpretation

Preoperative pain and depressive symptoms are associated with increased risk of delirium, independently and with substantial interaction, which suggests a cumulative effect. These factors should be assessed before surgery.

Funding

US National Institute on Aging.

Introduction

Delirium is characterised by acute decline in attention and cognitive function, and is a common complication of surgery in elderly adults (age 65 years and older), among whom incidence is 11–51%.¹ Adverse outcomes associated with postoperative delirium include prolonged length of hospital stay, institutionalisation, mortality, functional decline, and long-term cognitive impairment.1, 2 As the population of older adults undergoing surgical procedures continues to grow,³ improved understanding of risk factors for delirium becomes increasingly important.

Depression is a well recognised risk factor for delirium, with risk in some studies having been increased by two to three times.4, 5 Comorbid depression and delirium are associated with worse outcomes than with either syndrome alone.⁶ Depression also correlates with increased pain,⁷ which is underdiagnosed and undertreated in elderly people despite being linked to poor outcomes.⁸ The relation between pain and delirium has mostly been described in studies of acute pain experienced during hospital stay, with reports of risk of delirium being increased by up to nine times in patients with severe pain.⁹ Only two studies have assessed the association between preoperative pain and delirium.10, 11

In view of the associations between pain and depression, delirium and depression, and delirium and acute pain, an in-depth investigation of the inter-relationship between preoperative pain, depression, and delirium seemed warranted. We did a prospective study to assess whether preoperative pain and depression at baseline were risk factors for delirium, and to characterise their respective contributions.12, 13 We tested the hypothesis that the combination of severe pain and depression symptoms before surgery would be associated with an increased risk of postoperative delirium.