title: Lidocaine use in ultrasound-guided femoral nerve block: what is the minimum effective anaesthetic concentration (MEAC90)?
abstract: BACKGROUND
  This study aimed to estimate the minimum effective anaesthetic concentrations of lidocaine required to block the femoral nerve under ultrasound (US) guidance in 90% (MEAC90) of patients.
  
  
  METHODS
  A minimum of 45 patients who had undergone knee arthroscopy were included in this observational study. All the patients received US-guided sciatic, obturator, and femoral nerve blocks. The femoral nerve block was performed using 15 ml of lidocaine. The lidocaine concentration given to a patient was determined by the response of the previous patient (a biased-coin design up-down sequential method). If a patient had a negative response, the lidocaine concentration was increased by 0.1% w/v in the next patient. If a patient had a positive response, the next patient was randomized to receive the same lidocaine concentration (with a probability of 0.89) or to receive a concentration 0.1% w/v less (with a probability of 0.11). A positive response was defined as complete sensory and motor block. The patients' responses were analysed to calculate the mean MEAC90.
  
  
  RESULTS
  Fifty-two patients were required to complete the study; 45 had a positive response and seven had a negative response. The mean MEAC90 was estimated to be 0.93% w/v [95% confidence interval (CI), 0.8-1.03%]. Lidocaine 0.93% w/v was estimated to produce a successful block in 89% (95% CI, 78-100%) of patients.
  
  
  CONCLUSIONS
  Perineural injection of 15 ml of lidocaine 0.93% w/v under US guidance could provide successful femoral nerve block in 90% of patients.
authors: Department of Anaesthesia, Ain Shams University, Cairo, Egypt. ahmadtaha@sportsmedicine.ae
authors: A M
authors: AM
authors: Taha
authors: A M
authors: AM
authors: Abd-Elmaksoud
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000779:Anesthetics, Local / Q000008:administration & dosage*; D005260:Female; D005267:Femoral Nerve; D006801:Humans; D008012:Lidocaine / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D018084:Ultrasonography, Interventional
chemical_list: D000779:Anesthetics, Local; D008012:Lidocaine
keywords: anaesthetic techniques, regional, femoral; anaesthetics local, lidocaine; equipment, ultrasound machines