title: The effect of parturient height on the median effective dose of intrathecally administered ropivacaine.
abstract: BACKGROUND
  Pain during cesarean delivery is one of the more common reasons for a successful medicolegal claim. However, creating an extensive block area can result in hypotension, so determining the precise dose of local anesthetic is critical.
  
  
  OBJECTIVE
  Investigate effects of parturient height on the median effective dose (ED50) of intrathecally-administered ropivacaine.
  
  
  METHODS
  Prospective cross-sectional analytic study.
  
  
  METHODS
  Anesthesiology department in a provinicial hospital in China.
  
  
  METHODS
  Parturients undergoing cesarean delivery under combined spinal and epidural anesthesia were stratified according to height as follows: 150 cm to 155 cm, 156 cm to 160 cm, 161 cm to 165 cm and 166 cm to 170 cm. The spinal component of the anesthetic was established by bolus administration of up-and-down doses of 0.75% plain ropivacaine as determined by the Dixon method. The initial dose of ropivacaine was 5.79 mg and the testing interval dose change was set at 0.75 mg. The block height for the first cold feeling at T5 was considered satisfactory anesthesia.
  
  
  METHODS
  ED50 values and vasopressor requirements, nausea, vomiting and shivering.
  
  
  RESULTS
  In 120 parturients, the ED50 for satisfactory block height using intrathecal ropivacaine was 5.92 mg (95% confidence interval[CI] 5.02-6.86 mg) patients of 150 to 155 cm in height; 6.52 mg (95% CI 5.45-7.65 mg) in 156 cm to 160 cm; 7.49 mg (95%CI 6.83-8.25 mg) in 161 cm to 165 cm; 8.35 mg (95%CI 7.55-9.23 mg) in 166 to 170 cm. The ED50 of ropivacaine increased with increasing height of the subject. There were no significant differences in incidence of hypotension, vasopressor requirements, nausea, vomiting and shivering.
  
  
  CONCLUSIONS
  The ED50 of intrathecal ropivacaine using sensitivity to cold sensation increased with parturient height, indicating that dose may be determined in part by height.
  
  
  CONCLUSIONS
  The ED95 rather than the ED50 for spinal anesthesia is more useful clinically. We did not control for the effect of weight on the dose of local anesthetic. Factors such as baricity, volume, concentration injected, temperature of the solution, and viscosity can affect intrathecal spread of the local anesthetics and block quality.
authors.affiliation: Xiangdi Yu, Associate Professor, Department of Anesthesiology, Guizhou Provincial People's Hospital,, No 83 Zhongshan Eastern Road,, Guiyang, Guizhou 550002 China, T: +8618212004663, xiangdi_yu@163.com, ORCID: http://orcid.org/0000-0001-5010-3145.
authors.forename: Xiangdi
authors.initials: X
authors.lastname: Yu
authors.forename: Fangxiang
authors.initials: F
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000577:Amides / Q000008:administration & dosage* / Q000009:adverse effects; D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects; D001827:Body Height; D002585:Cesarean Section; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007022:Hypotension / Q000139:chemically induced / Q000517:prevention & control; D009325:Nausea / Q000139:chemically induced; D011247:Pregnancy; D011446:Prospective Studies; D000077212:Ropivacaine; D012768:Shivering / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000627:therapeutic use; D014839:Vomiting / Q000139:chemically induced; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D000077212:Ropivacaine