title: Postoperative pain significantly influences postoperative blood loss in patients undergoing total knee replacement.
abstract: OBJECTIVE
  Although hypertension has long been recognized as a factor that might increase intraoperative blood losses in major orthopedic surgery, the effects of postoperative pain-induced hypertension on blood losses have not so far been evaluated. The aim of this study was to evaluate the effect of pain on perioperative blood losses of patients undergoing primary total knee replacement (TKR).
  
  
  METHODS
  Data from patients participating in a randomized clinical trial comparing intravenous patient-controlled analgesia (PCA) (N = 20) with PCA plus continuous femoral nerve (three-in-one) block (N = 20) or PCA plus continuous posterior lumbar plexus (psoas compartment) block (N = 20) were prospectively and retrospectively collected. Correlations between relevant variables and measured and calculated blood loss, number of transfused unit, and late (96 hours) postoperative hemoglobin were tested by linear regressions. Stepwise regressions for each of the four above-mentioned goals were constructed using a probability to enter of 0.25 and to leave of 0.1. A P < 0.05 was considered significant.
  
  
  RESULTS
  At the stepwise regressions there was a significant positive correlation between measured blood losses and morphine consumption from 12 to 18 hours (P = 0.006); between calculated blood loss and preoperative mean arterial blood pressure (P = 0.01) and preoperative hemoglobin value (P = 0.02); and between late postoperative hemoglobin and body weight (P = 0.047).
  
  
  CONCLUSIONS
  In patients undergoing TKR, there is a significant correlation between measured blood loss and morphine consumption from 12 to 18 hours. It is concluded that postoperative pain significantly influences postoperative blood loss in patients undergoing TKR.
authors.affiliation: Department of Anesthesiology, Maisonneuve-Rosemont Hospital, University of Montreal, 5415 L'Assomption Boulevard, Montreal, Quebec, Canada. joanne.guay@umontreal.ca
authors.forename: Joanne
authors.initials: J
authors.lastname: Guay
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000577:Amides / Q000008:administration & dosage; D000700:Analgesics / Q000008:administration & dosage*; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D005260:Female; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D006973:Hypertension / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D007260:Infusion Pumps / Q000706:statistics & numerical data; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage; D009407:Nerve Block / Q000379:methods / Q000706:statistics & numerical data; D010149:Postoperative Pain / Q000150:complications* / Q000188:drug therapy* / Q000503:physiopathology; D019106:Postoperative Hemorrhage / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D011446:Prospective Studies; D012189:Retrospective Studies; D000077212:Ropivacaine; D012646:Self Administration; D016896:Treatment Outcome
chemical_list: D000577:Amides; D000700:Analgesics; D006454:Hemoglobins; D009020:Morphine; D000077212:Ropivacaine