TABLE 2.

Circadian rhythms in different types of acute pain.

Author	Type of pain	Study design; Number of participants	Results
Aya et al. 6	Labor pain	Observational cohort; 222 pregnant women	Women who experienced labor pain in the morning from 7:00 to 13:00 had an average visual analogue pain score of 75.6 when compared to 87.6 for women in evening.
Costa‐Martins et al. 7	Labor pain	Prospective observational study; 81 pregnant women	Greater labor pain severity, longer latency phase of labor as well as shorter duration of analgesics efficacy at night.
Desai et al. 8	Labor pain	Prospective cohort; 1657 pregnant women	Greater labor pain scores before epidural analgesia in evenings and nights than mornings (6.67 ± 2.5) and afternoons
Debon et al. 9	Labor pain	Observational cohort; 194 pregnant women	No significant difference for labor pain assessed by VAS before epidural administration of ropivacaine between different circadian groups of patients. Longer duration of analgesia in the morning and afternoon groups than night and evening groups
Rigas et al. 10	Biliary colic	Observational cohort; 50 participants	Pain follows a circadian periodicity with the peak pain at 00:25
Minoli et al. 11	Biliary colic	Observational cohort; 54 participants	Pain was found to follow a circadian pattern with a peak occurring at 21:30
Boscariol et al. 12	Postoperative: hysterectomy	Randomized, parallel, controlled; 103 patients	Day 1 postop, all types of pain were worst at 08:00 compared to 12:00, 16:00 and 20:00 Day 2 postop, morphine requirement was increased at 08:00 and 12:00 compared to 16:00 and 20:00
Song et al. 13	Postoperative: abdominal surgery	Randomized controlled; 84 patients	Morning operations (8:00–12:00) required a higher dose of anesthetic drugs than evening operations (18:00–22:00)
Kwon et al. 14	Postoperative: hip surgery	Randomized controlled; 44 patients	No significant difference between groups in terms of pain scores at any time point