I have appreciated the geriatric articles including Dr Chan’s review of delirium [BCMJ 2011;53:409-415 [9]]. 

My concern is that the article made no mention of pain as a cause of delirium. 

The article notes that dementia is the most common predisposing factor for delirium. With increasing dementia there is less reporting of pain by the patient and staff[1] and less use of analgesics.[2,3] 

Dr Chan notes that hip fracture and cardiac surgeries confer a higher risk of delirium. A study of 514 hip fracture patients, in which 16% subsequently became delirious, re­vealed that in those who could self-report pain the most predictive factor for developing delirium was severe pain.[4] Low doses of opioids were also predictive for delirium in both those able and unable to report pain.

Studies that implicate opioids as the cause of delirium in older adults assume that if a person is on opioids pain is no longer present and not a cause of delirium. The adequacy of analgesic prescribing can be measur­ed with the pain management index (PMI), a measure of the congruence between the patient’s reported pain level and the strength of the analgesic they are receiving.[5] 

A review of 2011 patients with metastatic bone pain in Canada showed that 25% of patients on opioids for moderate to severe pain were undertreated—in other words, still in pain even though they were on opioids.[6] Most clinicians readily use opioids in cancer pain and these patients had access to palliative care teams, so this is likely a significant underestimate of the percentage of noncancer patients on opioids who are still in significant pain.

I would urge all clinicians to always consider uncontrolled pain as a reason for delirium in older adults—particularly in those who are cognitively impaired—and even if they are already on opioids.
—Romayne Gallagher, MD
Vancouver

References

1. Parmelee PA. Pain in cognitively impaired older persons. Clin Geriatr Med 1996 Aug;12:473-487.
2. Won A, Lapane K, Gambassi G, et al. Correlates and management of nonmalignant pain in the nursing home. SAGE Study Group. Systematic Assessment of Geriatric Drug Use via Epidemiology. J Am Geriatr Soc 1999;47:936-942.
3. Bernabei R, Gambassi G, Lapane K, et al. Management of pain in elderly patients with cancer. SAGE Study Group. Systematic Assessment of Geriatric Drug Use via Epidemiology. JAMA 1998;279:1877-1882.
4. Morrison RS, Magaziner J, Gilbert M, et al. Relationship between pain and opioid analgesics on the development of delirium following hip fracture. J Gerontol A Biol Sci Med Sci 2003;58:76-81.
5. Cleeland CS, Gonin R, Hatfield AK, et al. Pain and its treatment in outpatients with metastatic cancer. N Engl J Med 1994;330:592-596.
6. Mitera G, Fairchild A, DeAngelis C, et al. A multicenter assessment of the adequacy of cancer pain treatment using the pain management index. J Palliat Med 2010;13:589-593.