The impact of delirium on the circadian distribution of breakthrough analgesia in advanced cancer patients.

Most cancer patients will experience pain requiring opioid therapy during their illness. Standard opioid therapy includes fixed scheduled doses and so-called "rescue" doses for breakthrough pain. Circadian rhythms seem to influence the expression of pain and the responsiveness to analgesic medication. Delirium is a common complication in advanced cancer patients and it also may modify the expression of pain and the use of analgesic medication. We reviewed the circadian distribution of breakthrough analgesia (BTA) doses in 104 advanced cancer patients who were part of a prospective study of the occurrence of delirium. We found that the circadian distribution of BTA is significantly different from a random distribution in the case of patients with and without delirium. Patients without delirium tended to use more BTA (P < 0.001) in the morning, whereas patients with delirium tended to use more BTA in the evening and at night (P = 0.02). We conclude that delirium is associated with changes in the circadian distribution of BTA, which is possibly related to reversal of the normal circadian rhythm.