Which of the following local anaesthetic is the shoest acting which aids in obstetric anaesthesia?
**Core Concept**
Lidocaine, mepivacaine, and chlorprocaine are commonly used local anesthetics in obstetric anesthesia. The duration of action of these agents is determined by their lipid solubility, protein binding, and metabolism. A shorter-acting local anesthetic is desirable in obstetric anesthesia to minimize fetal and maternal toxicity.
**Why the Correct Answer is Right**
Chlorprocaine is a short-acting ester local anesthetic, primarily metabolized by plasma cholinesterase. It has a rapid onset and short duration of action, typically lasting around 30 minutes. This makes it an ideal choice for obstetric anesthesia, as it allows for quick recovery and minimal systemic toxicity. Chlorprocaine's short duration of action is due to its rapid hydrolysis by cholinesterase, which breaks down the drug into its inactive metabolites.
**Why Each Wrong Option is Incorrect**
**Option A:** Lidocaine is a longer-acting amide local anesthetic, with a duration of action typically exceeding 1 hour. It is not the shortest-acting local anesthetic, making it a less desirable choice for obstetric anesthesia.
**Option B:** Mepivacaine is another amide local anesthetic with a duration of action similar to lidocaine, making it less suitable for short procedures like obstetric anesthesia.
**Option C:** This option is blank. Please fill it in.
**Clinical Pearl / High-Yield Fact**
When choosing a local anesthetic for obstetric anesthesia, consider the duration of action, lipid solubility, and metabolism. Shorter-acting agents like chlorprocaine are ideal for minimizing fetal and maternal toxicity.
**Correct Answer:** C. Chlorprocaine is the shortest-acting local anesthetic which aids in obstetric anaesthesia.