Effects of single shot femoral nerve block combined with intrathecal morphine for postoperative analgesia: a randomized, controlled, dose-ranging study after total knee arthroplasty.

OBJECTIVE Pain after total knee arthroplasty (TKA) is severe, thus adequate pain control can be a challenge. Intrathecal morphine (ITM) provides excellent postoperative analgesia for TKA, but may have side effects. Femoral nerve block (FNB) also has been used for postoperative analgesia in TKA. We examined postoperative analgesia efficacy and side effects of ITM combined with single shot femoral nerve block (SSFNB) after TKA, over the dosage range of 0.0 to 0.3 mg. MATERIAL AND METHOD Sixty patients undergoing elective TKA received SSFNB (0.5% bupivacaine 20 ml) and spinal anesthesia with 15 mg of hyperbaric bupivacaine (0.5% Heavy Marcaine) were included in this study. They were randomized to receive ITM (0, 0.1, 0.2, and 0.3 mg). A patient-controlled analgesia (PCA) device provided additional intravenous morphine. Morphine consumption, pain score, and side effects were recorded at 0, 1, 4, 8, 12, and 24 hour postoperative. Patient satisfaction was rated at the 24-hour postoperative visit. RESULTS Morphine consumption was significant higher in 0 mg ITM group (control) than other groups, but there was no difference between ITM groups. Pain score was significant lower in 0.3 mg ITM group compared to 0 mg at 1 hour (0.5 vs. 3.5, respectively; p-value = 0.013) and 4 hour (1.5 vs. 4.5, respectively; p-value = 0.037) postoperative period Side effects were not different in all groups. CONCLUSION The present study concluded that, low-dose ITM combination with SSFNB provided good pain relief with low side effects and reduced morphine consumption during the first 24 hours post TKA.