Effectiveness of continuous versus single injection femoral nerve block for total knee arthroplasty: A double blinded, randomized trial.

BACKGROUND: Effective analgesia following total knee arthroplasty (TKA) is important for maximizing patient satisfaction, early participation in physical therapy and reducing the hospital stay. This trial compared continuous catheter femoral nerve block (cFNB) to single injection femoral nerve block (sFNB) in terms of analgesia, opioid consumption, and participation in physical therapy and associated side effects. METHODS: This randomized, double blinded trial was conducted in a non-university hospital setting, without major changes to anesthesia or surgical clinical pathways. A total of 85 patients scheduled for primary TKA were randomized to receive either cFNB (n=44) or sFNB (n=41). All patients had FNB with 0.5% ropivacaine bolus followed by subarachnoid block for surgery. Postoperatively, 0.2% ropivacaine infusion was commenced in cFNB group and a sham catheter was taped to the skin in sFNB group. All patients received a structured multimodal analgesia regimen throughout hospital stay. The primary outcomes were peak resting visual analogue scale (VAS) scores and morphine consumption at 48h postoperatively. RESULTS: VAS scores (Mean difference 0.25, 95% Confidence Interval (CI) -0.56 to 1.06; [P=0.196]) and morphine consumption (Mean difference 0.95mg, 95% CI -9.99 to 11.89; [P=0.863]) were not significantly different among patients who received cFNB versus sFNB at 48h. There was no difference in hospital stay (P=0.517) or long-term functional recovery between the two groups (P=0.385). CONCLUSIONS: sFNB block provides equal pain relief compared with cFNB, after TKA with no significant difference in opioid consumption, hospital stay, physical therapy outcomes or associated side effects.

Mitochondrial injury and caspase activation by the local anesthetic lidocaine.

BACKGROUND: Lidocaine, a local anesthetic, can be neurotoxic. However, the cellular mechanisms of its neurotoxicity at concentrations encountered during spinal anesthesia remain unclear. METHODS: The authors examined the mechanisms of lidocaine neurotoxicity in the ND7 cell line derived from rat dorsal root ganglion. Individual neurons were assayed by flow cytometry or microscopy using fluorescent probes of plasma membrane integrity, mitochondrial membrane potential, caspase activity, phospholipid membrane asymmetry, and mitochondrial cytochrome c release. RESULTS: In the ND7 cell line, lidocaine at 185 mm x 10 min to 2.3 mm x 24 h caused necrosis or late apoptosis. Equimolar Tris buffer and equipotent tetrodotoxin controls were not toxic, indicating that neither osmotic nor Na-blocking effects explain lidocaine neurotoxicity. The earliest manifestation of lidocaine neurotoxicity was complete loss of mitochondrial membrane potential within 5 min after exposure to lidocaine at a concentration of 19 mm or greater. Consistent with these data, 37 mm lidocaine (1%) induced release of mitochondrial cytochrome c into the cytoplasm, as well as plasma membrane blebbing, loss of phosphatidylserine membrane asymmetry, and caspase activation, with release of mitochondrial cytochrome c to the cytoplasm within 2 h. Treatment with z-VAD-fmk, a specific inhibitor of caspases, prevented caspase activation and delayed but did not prevent neuronal death, but did not inhibit the other indicators of apoptosis. CONCLUSIONS: Collectively, these data indicate that lidocaine neurotoxicity involves mitochondrial dysfunction with activation of apoptotic pathways.