Femoral nerve blockade using various concentrations of local anesthetic for knee arthroscopy in the pediatric population

BACKGROUND: Femoral nerve blockade (FNB) provides effective postoperative analgesia in children undergoing arthroscopic knee surgery as evidenced by their opioid-sparing effects and decreased postoperative pain scores. Increasing the local anesthetic concentration in peripheral nerve blockade for adults undergoing orthopedic surgery has been shown to be beneficial, increasing block success rate, and providing a longer duration of analgesia. The effect of increasing the concentration of local anesthetic in extremity blocks in children remains largely unexplored. METHODS: We retrospectively evaluated the effectiveness of FNB using three concentrations of local anesthetic (ropivacaine 0.2%, bupivacaine 0.25%, and ropivacaine 0.5%) in children and adolescents undergoing arthroscopic knee surgery. The primary outcome evaluated was postoperative opioid consumption before discharge. Secondary outcomes included post-anesthesia care unit (PACU) and hospital discharge times, first pain score in PACU, and the incidence of adverse events. RESULTS: Two hundred and sixty-nine children and adolescents who received a FNB for arthroscopic knee surgery from January 2010 to December 2013 were included for analysis. Local anesthetic used in FNB was ropivacaine 0.2% in 116 (43%) cases, ropivacaine 0.5% in 75 (28%) cases, and bupivacaine 0.25% in 78 (29%) cases. Median postoperative opioid consumption (mg/kg intravenous morphine equivalents) in the ropivacaine 0.5% group was 0 mg/kg (interquartile ranges [IQR]: 0 mg, 0.03 mg/kg) compared to 0.02 mg/kg (IQR: 0, 0.08 mg/kg) in the ropivacaine 0.2% group and 0.01 mg/kg (IQR: 0, 0.08 mg/kg) in the bupivacaine 0.25% group (p=0.009). Median PACU time was shortest in the ropivacaine 0.5% group (47 min; IQR: 36, 68 min) compared to the ropivacaine 0.2% (58 min; IQR: 41, 77) and bupivacaine 0.25% (54 min; IQR: 35, 75 min) groups (p=0.040). Among groups, there were no significant differences in first postoperative pain scores or incidence of nausea and vomiting. No patient in any group experienced a serious adverse event. CONCLUSION: The results suggest that ropivacaine 0.5% for FNB offers superior postoperative analgesia in the form of decreased postoperative opioid consumption and earlier PACU/hospital discharge, when compared to ropivacaine 0.2% and bupivacaine 0.25% in the pediatric population. LEVEL OF EVIDENCE: III, Retrospective Comparative Study.