Intermittent Bolus Versus Continuous Paravertebral Infusion on Postoperative Pain after Unilateral Mastectomy: A Retrospective Cohort Study

Background: Persistent pain is a common complication after mastectomy for breast cancer, and postoperative analgesia through paravertebral infusion is a promising technique for pain control after mastectomy. Although paravertebral local anesthetic infusion can be performed using continuous or intermittent bolus modes, there is no evidence of superiority of either infusion mode.Methods: We retrospectively studied patients who had undergone unilateral mastectomy with paravertebral catheter placed for postoperative analgesia between October 2017 and September 2018. Logistic regression was created to estimate the relative risk for moderate to severe pain defined by average pain scores greater than 4 using a 0 to 10 Numeric Rating Scale (NRS) within first 24 hours after surgery. Opioid consumption was compared using a Student T-test for difference in means using the log-transformed cumulative opioid consumption converted to milligrams of oral morphine equivalents (OME) within the first 48 hours after surgery.Results: 49 patients were included (continuous infusion group: 14; bolus infusion group: 35). Bolus paravertebral infusion was associated with reduction of relative risk of moderate to intense pain (adjusted relative risk: -0.96; 95%CI: -1.81, -0.1; p = 0.029) but there was no association with reduction in opioid consumption (difference of means: -1.4mg of OME; 95%CI: -2.78, 1.42; p = 0.33).Conclusion: Intermittent bolus infusion was associated with reduction of relative risk for moderate to severe postoperative pain for unilateral mastectomies. Therefore, paravertebral catheter infusion modality may influence postoperative pain experience after unilateral mastectomies.