Abstract
ObjectivesCurrent literature is in disagreement regarding female sex as a risk factor for pain after surgery. We hypothesized, that sex differences exist but that they are influenced by certain factors. Here, we investigated the influence of sex for different clinically relevant postoperative pain (POP) outcome parameters and evaluated the role of assumed confounders for sex differences.MethodsFrom 1372 screened patients undergoing orthopedic surgery at the university hospital of Muenster between March 2010 and June 2011, 890 patients were included. The validated International Pain Outcomes questionnaire was used to assess the role of sex for several aspects of POP including pain severity, physical and emotional functional interference as well as the patient’s perceptions of the care they received on the first day after surgery. Assessed confounders were age, preoperative chronic pain, anesthetic technique employed and surgical procedure. All statistical analyses were performed with SPSS Statistics Software 22.ResultsLinear regression analysis demonstrated that sex was a statistically significant risk factor for “worst pain since surgery”. Additionally, significant sex differences in “time spent in severe pain”, “feeling anxious due to pain”, “feeling helpless due to pain” and “opioid consumption since surgery” could be identified. An univariate general linear model showed that “age” and “preoperative pain” were significant confounders for sex differences. Further descriptive subgroup analysis revealed consistent sex differences for several POP outcome variables especially in patients older than 50 years or patients with preoperative chronic pain. However, sex differences disappeared in younger patients and in patients without preoperative pain.DiscussionOur data confirmed that sex differences exist in pain intensity and frequency, pain interference with feelings and opioid consumption during the first 24 hours postoperatively. However, sex differences were significantly influenced by the factors “age” and “preoperative pain”. These findings may in part explain why clinical studies get different results related to sex differences and renders specific awareness in older women and female patients with preoperative chronic pain.
Highlights
More than 240 million surgical procedures are performed worldwide every year [1] and pain guidelines and evidence-based recommendations have been made to improve postoperative pain (POP) management [2]
Significant sex differences in “time spent in severe pain”, “feeling anxious due to pain”, “feeling helpless due to pain” and “opioid consumption
As secondary outcome we investigated the time the patient spent in severe pain since surgery (NRS 0% = “never in severe pain”– 100% = “always in severe pain”), functional disability due to pain (NRS 0 = “did not interfere”– 10 = “completely interfered”), anxiety and helplessness caused by the pain (NRS 0 = “not at all”– 10 = “extremely”), cumulative opioid consumption since surgery calculated by conversion of opioid requirements into morphine equivalents (ME), the degree of pain relief through pain treatment (NRS: 0% = “no relief”– 100% = “complete relief”), wish for more pain treatment (“yes or no”) and satisfaction with the results of pain treatment (NRS 0 = “extremely dissatisfied”– 10 = “extremely satisfied”)
Summary
More than 240 million surgical procedures are performed worldwide every year [1] and pain guidelines and evidence-based recommendations have been made to improve postoperative pain (POP) management [2]. One of the reasons for this unsatisfactory situation might be an underestimated role of risk factors for a poor postoperative pain outcome. One factor increasing the risk to experience more severe pain after surgery is the (female) sex of the patient. In some studies women tended to report more pain both at rest and during movement after surgery compared to men, but this trend is not consistent throughout the literature [7,8,9]. Morphine seems to be more effective in women compared to men [10], clinical trials investigating sex differences of perioperative morphine consumption showed conflicting results [7,8,9, 11]
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