Minimum Effective Dose of Ropivacaine for Spinal Anesthesia for Cesarean Delivery
Condition: Spinal Anesthesia
Study type: Interventional

Summary: 
      Ropivacaine is one of commonly used anesthetics for spinal anesthesia. Usually L2-3 or L3-4
      intervertebral space is chosen for spinal anesthesia. The efficacy of ropivacaine injected
      into subarachnoid space depends on the given dose and the chosen intervertebral space.
      Appropriate dose could satisfy the requirement of operation and reduce incidence of the
      adverse reaction. But it is not certain about the minimum effective dose of ropivacaine in
      cesarean section through the two intervertebral spaces, respectively. This study is being
      conducted to find the minimum effective doses for L2-3 and L3-4 spinal anesthesia in cesarean
      section.
    

Detailed description: 
      Some unexpected adverse reactions such as respiratory depression, vomiting, especially supine
      hypotensive syndrome could caused by a high dose of anesthetic in cesarean section. The
      investigators assumed that there be a minimum effective dose that will be associated with the
      best possible performance of ropivacaine for different intervertebral spaces(L2-3 and L3-4 in
      usual). That maybe enhance the comfort of parturient and safety of fetus.

      This study is conducted as a prospective, randomized, up-down sequential dose of isobaric
      ropivacaine in 3 mL that will provide effective analgesia for 50% of parturients in cesarean
      section. The investigators use the combined spinal-epidural anesthesia(CSEA) technique in the
      study. The initial dose of ropivacaine is chosen as 12 mg in L2-3 group and 15 mg in L3-4
      group, and the testing interval is 0.5 mg with subsequent doses being determined by the
      outcome of the previous injection in the same group. If the previous response is ineffective,
      the next patient will receive 0.5 mg more than the last patient. If the response of the
      previous patient is effective, the next patient decrease 0.5mg.

      The visual analogue scale (VAS) is used to rate the pain, where 0 is no pain and 10 is the
      worst pain imaginable. Criteria for evaluation:(1) effective: after spinal anesthesia finish,
      a dose that provide adequate sensory dermatomal anesthesia to pinprick to T6 or higher within
      10 minutes, and the VAS is lower than or equal to 3 within 60minutes after skin incision; (2)
      ineffective: if the initial plane of sensory dermatomal anesthesia is lower than T6 or VAS is
      greater than 3 within 60 minutes after skin incision, the dose of ropivacaine is considered
      inadequate and additional lidocaine is given through epidural catheter.

      Motor assessments are performed at the start of operation. Motor block in the lower limb is
      assessed by a modified Bromage scale (0=no paralysis, 1=unable to raise extended leg,
      2=unable to flex knee,3=unable to flex ankle). All of the assessments are made by an
      anesthetist who is blinded to the group assignment as well as to the dose injected.

      On the other hand, the investigators will compare the incidence of adverse reaction between
      the L2-3 and L3-4 group.

      Using the Dixon and Massey up-and-down method study design, 60 patients scheduled for
      elective cesarean section will be included in the study, 30 for each group.
    

Intervention name(s): Intervertebral space; Ropivacaine
Intervention type(s): Procedure; Drug
Intervention description(s): The initial dose of ropivacaine is chosen as 12 mg in L2-3 group and 15 mg in L3-4 group with the volume of 3 mL in both groups. The testing interval is 0.5 mg with subsequent doses being determined by the outcome of the previous injection in the same group.If the previous response is ineffective, the next patient will receive 0.5 mg more than the last patient. If the response of the previous patient is effective, the next patient decrease 0.5mg.
Other intervention name(s): Naropin
Intervention MeSH terms: Ropivacaine
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment
Keywords: cesarean delivery; ropivacaine; minimum effective dose; dose-response relationship; intrathecal; intervertebral space