Minimum Local Anesthetic Volume of Bupivacaine in Labour Epidurals
Condition: Acute Pain
MeSH terms: Acute Pain
Study type: Interventional

Summary: 
      Different medications can be used as analgesics in labor epidurals. Bupivacaine is one of the
      most commonly used drugs for that purpose. The efficacy of a certain medication injected
      epidurally depends on the dose that is given. A certain dose can be administered in different
      concentrations, which will consequently mean different volumes. Our hypothesis is that for
      each concentration of a certain drug, there has to be a minimum effective volume that will be
      associated with the best possible performance of the drug. This study is being conducted to
      find the minimum volume of bupivacaine (a local anesthetic) that produces successful
      analgesia in 95% of patients in labor.
    

Detailed description: 
      Epidural administration of local anesthetics during labor produces analgesia, sympathetic
      block and motor block. The characteristics of the block depend on the volume and
      concentration of the local anesthetic that is used as well as the potential use of adjuncts.
      Although many researchers have investigated the efficacy of different drugs at different
      concentrations, the volumes used have been arbitrary. There is limited data regarding the
      minimum volume that is necessary for a successful anesthetic for a given concentration of
      bupivacaine.

      This study is conducted as a prospective, randomized, up-down sequential allocation trial.
      The aim is to determine the minimum volume of 0.125% bupivacaine that will provide effective
      analgesia for 95% of parturients in the first stage of labor. The verbal numeric rating scale
      (VNRS) is used to rate the pain felt over the first 20 minutes, where 0 is no pain and 10 is
      the worst pain imaginable. After 20 minutes, if the VNRS was greater than 2, the volume of
      bupivacaine was considered inadequate and additional medication was given.

      The volume of bupivacaine for the first patient was arbitrarily chosen as 8 ml, and the dose
      for each subsequent patient depends on the outcome of the previous injection. Doses will be
      increased or decreased in increments of 1 ml. If the previous response was ineffective, the
      next patient will receive 1 ml more than the last patient. If the response of the previous
      patient is effective, the Narayana rule, which is used to cluster doses around EV95, will be
      applied to determine if the dose remains the same or decreases.

      50 patients will be included in the study. An estimate of EV95 will be calculated based on a
      logistic model with non-log-transformed doses, fit using Firth's penalized maximum likelihood
      approach for small sample bias correction. Confidence intervals will be calculated based on
      the profile likelihood approach.
    

Intervention name(s): bupivacaine
Intervention type(s): Drug
Intervention description(s): 0.125% bupivacaine in a volume determined according to the biased coin up-down sequential allocation model, starting at 8mL.
Intervention MeSH terms: Bupivacaine
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: Epidural; Labor Analgesia; Bupivacaine; Dose-response; Minimum effective volume