title: Determination of the median effective dose (ED50) of spinal plain ropivacaine for motor block in adults.
abstract: BACKGROUND
  The median effective dose (ED50) for motor blockade of spinal plain bupivacaine in adults was previously reported; however, that of ropivacaine is unknown. This study aimed to determine the ED50 for motor blockade of spinal plain ropivacaine in adults, evaluating the effect of age on this parameter.
  
  
  METHODS
  133 patients in need of combined spinal and epidural anesthesia were enrolled in this sequential allocation study. They were divided into 6 groups according to age: 20-30, 31-40, 41-50, 51-60, 61-70, and 71-80 years. Using the up-and-down method of Dixon, the ropivacaine dose was varied according to the preceding patient's reaction. The modified Bromage and hip motor function score was used to evaluate the degree of motor block after administration of ropivacaine. ED50 values were estimated by the method of Dixon and Massey. Other indexes, including the onset of motor block, the analgesia level, and the duration of motor block were also assessed.
  
  
  RESULTS
  the ED50 for motor block of intrathecal ropivacaine was 20.96 mg (95 % CI: 19.83-22.16 mg) in 20-30, 19.05 mg (95 % CI: 18.43-19.70 mg) in 31-40, 17.91 mg (95 % CI: 17.10-18.76 mg) in 41-50, 17.91 mg (95 % CI: 16.49-19.44 mg) in 51-60, 16.11 mg (95 % CI: 14.50-17.90 mg) in 61-70, and 15.75 mg (95 % CI: 13.98-17.73 mg) in 71-80 year-old patients. Maximum cephalic analgesic effects were obtained at the L4-T6 and L4-T2 levels, at 5 and 10 min, respectively, after intrathecal administration of ropivacaine in all groups.
  
  
  CONCLUSIONS
  the ED50 for motor block in spinal plain ropivacaine decreases with advancing age, indicating that age has an influence on the potency of spinal ropivacaine.
authors.affiliation: Department of Anesthesiology, The First College Of Clinical Medical Science, China Three Gorges University & Yichang Central People's Hospital , 443003, Yichang, Hubei, China. cmq2003@hotmail.com.
authors.forename: Ming-Quan
authors.initials: MQ
authors.lastname: Chen
authors.affiliation: Department of Anesthesiology, The First College Of Clinical Medical Science, China Three Gorges University & Yichang Central People's Hospital , 443003, Yichang, Hubei, China.
authors.forename: Chun
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Anesthesiology, The First College Of Clinical Medical Science, China Three Gorges University & Yichang Central People's Hospital , 443003, Yichang, Hubei, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Fang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000577:Amides / Q000008:administration & dosage*; D000775:Anesthesia, Spinal / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007278:Injections, Spinal; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D000077212:Ropivacaine; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine
keywords: Anesthesia; Intrathecal; Minimum local anesthetic; Motor block; Ropivacaine; Spinal