Determination of the Minimum Local Analgesic Dose of Spinal Chloroprocaine in Labour

Combined spinal-epidural (CSE) analgesia has become a widely accepted approach to provide analgesia for labour pain. Despite the increasingly widespread use of this technique, an optimal intrathecal drug regimen has not been established yet. Several investigations using local anesthetics such as Bupivacaine, Levobupivacaine and Ropivacaine in CSE during labour have been published. But despite the reintroduction of Chloroprocaine recently there haven't been any investigations about spinal chloroprocaine. Chloroprocaine is already a long-know drug with a beneficial pharmacodynamic/kinetic profile. It is known for a very quick onset of action (2 - 3 minutes), high efficacy, rapid metabolism by plasma cholinesterases and short half-life both in mother and fetus. Because of this beneficial profile, Chloroprocaine is widely used intrathecally for surgical anesthesia. Several investigations demonstrate that for surgical anesthesia doses Chloroprocaine ranging from 30 - 60 mg are used and that they have an effective surgical duration of 40 - 90 minutes. Despite these "standards" for surgical anesthesia, little is known about spinal Chloroprocaine dose regimens. Therefore the primary goal of this study is to determine the minimum adequate dose of Chloroprocaine that is to be given spinally to a woman in labour using a CSE procedure. We will use the up-down sequential allocation to identify the median effective dose (ED50) or concentration (EC50). The Effective dose in 95% of the population (ED95) can be estimated also from an up-down sequential allocation and will become an important valuable approximation of the clinical dose.