We observed an association between pain and incident delirium among critically ill adults. Exposure to morphine or fentanyl (but no other pain medications) was associated with increased risk of delirium occurrence.

From 8,054 citations, 90 studies (119,230 patients) published between 2001 and 2023 were included in the systematic review.

41 studies were included in the primary meta-analysis examining prevalent delirium: seven studies evaluated pain; 12 studies evaluated fentanyl; and five studies evaluated morphine.

There was a trend to association between pain and delirium occurrence (OR 2.49, 95% CI 0.98–6.30), and a significant association between pain and incident delirium (OR 3.70, 95% CI 1.73–7.93).

Fentanyl (OR 2.49, 95% CI 1.45–4.27) and morphine (OR 2.13, 95% CI 1.21–3.75) were associated with delirium occurrence.

Risk of bias was critical for many studies.

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