Development of a reliable mouse model for caudal epidural anesthesia

Epidural anesthesia is frequently used for pain management during surgery and childbirth. However, a persistent issue is fever induced by epidural anesthesia, a common complication in clinical settings, for which effective countermeasures are lacking. Developing a reliable mouse model is crucial for investigating the underlying mechanisms. This study focuses on developing a reproducible technique for administering caudal epidural anesthesia in mice. Male ddY mice were administered 0.25% ropivacaine in volumes of 50, 100, or 150 µL into the epidural space. Successful epidural puncture was confirmed by the presence of blue dye in the epidural space. Anesthetic effects were compared using the formalin test. Epidural success rates ranged from 45.5% to 63.6%, with the highest success in the 100 µL group. The lowest success rate was observed in the 50 µL group. The formalin test showed stable analgesia with 100 µL, while 150 µL produced a broader anesthetic effect but increased mortality. To address the anatomical and technical challenges of precise needle placement in small animals, we successfully performed caudal epidural anesthesia in mice by optimizing the puncture posture using a stereotaxic apparatus. Administration of 100 µL of 0.25% ropivacaine provided stable analgesia with minimal side effects. This technique is a valuable tool for studying the neurophysiological and mechanistic aspects of epidural anesthesia.