title: Chronobiological characteristics of postoperative pain: diurnal variation of both static and dynamic pain and effects of analgesic therapy.
abstract: BACKGROUND
  Previous postoperative investigations report morning peaks in analgesic administration. However, few studies have examined diurnal variation of both pain and analgesic consumption and little is known about dynamic pain in this context.
  
  
  METHODS
  The diurnal pattern of postoperative pain is described using pain intensity and analgesic consumption data from a recently published hysterectomy trial.
  
  
  RESULTS
  In the presence of patient-controlled analgesia with morphine, pain at 8 a.m. was significantly higher (P<0.05) than at noon, 4 p.m. or 8 p.m. on postoperative day one (for rest pain and pain evoked by sitting, forced expiration and cough) and on postoperative day two (for pain evoked by forced expiration and cough only). This temporal pattern was observed both with and without the co-administration of non-opioid analgesics (gabapentin and/or rofecoxib). Morphine use during the four hours preceding 8 a.m. on either postoperative day was not significantly lower than any of the other corresponding time intervals.
  
  
  CONCLUSIONS
  Based on data from our post-hysterectomy analgesic clinical trial, static and dynamic pain in the morning appears to be more intense than pain later in the day. This pattern was observed in the presence of substantial nocturnal morphine use. Based on these and other previous observations, specifically designed investigations are needed to better characterize the clinical, neurohormonal and neurophysiological features of postoperative circadian pain variation - including pain during sleeping hours. If the above observations are replicated, future study of nocturnal sustained-release opioids as well as time-shifting the administration of non-opioid co-analgesic drugs to the very early morning may be warranted.
authors.affiliation: Department of Anesthesiology, Queen's University, Kingston General Hospital, 76 Stuart Street, Kingston, Ontario K7L 2V7, Canada.
authors.forename: Rya
authors.initials: R
authors.lastname: Boscariol
authors.forename: Ian
authors.initials: I
authors.lastname: Gilron
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Orr
mesh_terms: D000588:Amines / Q000627:therapeutic use; D016058:Analgesia, Patient-Controlled; D000700:Analgesics / Q000627:therapeutic use; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D002940:Circadian Rhythm / Q000502:physiology*; D003509:Cyclohexanecarboxylic Acids / Q000627:therapeutic use; D052246:Cyclooxygenase 2 Inhibitors / Q000627:therapeutic use; D004334:Drug Administration Schedule; D005260:Female; D000077206:Gabapentin; D006801:Humans; D007044:Hysterectomy / Q000009:adverse effects*; D007783:Lactones / Q000627:therapeutic use; D009020:Morphine / Q000008:administration & dosage*; D010147:Pain Measurement / Q000379:methods; D010149:Postoperative Pain / Q000188:drug therapy* / Q000503:physiopathology; D016037:Single-Blind Method; D013450:Sulfones / Q000627:therapeutic use; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000627:therapeutic use
chemical_list: D000588:Amines; D000700:Analgesics; D000701:Analgesics, Opioid; D003509:Cyclohexanecarboxylic Acids; D052246:Cyclooxygenase 2 Inhibitors; D007783:Lactones; D013450:Sulfones; C116926:rofecoxib; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D009020:Morphine