Effect of wound infiltration with bupivacaine or lower dose bupivacaine/magnesium versus placebo for postoperative analgesia after cesarean section

AIM: The authors examined the analgesic effect of wound infiltration with bupivacaine or lower dose bupivacaine and magnesium versus normal saline for postoperative analgesia after cesarean section. MATERIALS AND METHODS: A total of 120 patients, American Society of Anesthesiologists (ASA) I-II were prepared for elective cesarean section. At the end of the surgery, the wound was continuously infiltrated at a rate of 5 ml/h for 24 h post-operatively by one of the following solutions: 0.25% bupivacaine, a mixture of 0.125% bupivacaine and 5% magnesium sulphate or normal saline (0.9%). Total opioid consumption, Visual Analogue Scale (VAS) at rest and movement, incidence of opioid side-effects and signs of wound inflammation were assessed during the period of the study (24 h post-operatively). Three months later, residual pain, surgical wound infection, need for extra-antibiotic therapy and wound healing impairment were assessed. RESULTS: Post-operative pain scores at rest were statistically significant higher in the control group than those in the both wound infiltration groups from 4(th) h and onwards (P < 0.0001). Meanwhile, post-operative pain was higher in bupivacaine group versus magnesium group (P < 0.0001, P < 0.0001, 0.0012, respectively). There was statistically significant increase in VAS during movement in the control group versus others at 2, 4, 12, 24 h post-operatively (P < 0.0001). However, patients received magnesium plus bupivacaine wound infiltration showed a significant decrease in post-operative pain scores than whom received bupivacaine from 4(th) h and onward (P < 0.0001, 0.0054, 0.0001, respectively). Morphine consumption was significantly reduced in the magnesium group, (P < 0.0001). Incidence of residual pain was comparable in the three groups. The incidence of sedation and urine retention were noted to be significantly higher in the control group in comparison to other groups, (P <0.0001). The incidence of post-operative nausea and vomiting was reduced in patients received magnesium plus bupivacaine block versus others (P < 0.0001). CONCLUSION: Continuous wound infiltration with a mixture of bupivacaine and magnesium sulphate after cesarean section showed an effective analgesia and reduced post-operative Patient Controlled Analgesia (PCA) requirements as compared to continuous wound infiltration with local anesthetic only or placebo with fewer incidences of opioid adverse effects.