Unilateral Spinal Anesthesia in a Repeat Cesarean Delivery: A Case Report.

General anesthesia increases the morbid risk for both mother and infant during a cesarean delivery. Failed or asymmetric blocks can force providers to turn to a general anesthetic precipitously. A true one-sided spinal block, with complete absence of anesthesia on one side despite correct subarachnoid technique, is rare and not well characterized in the literature. In this case, a 32-year-old multiparous woman presented for elective repeat cesarean delivery. After an uncomplicated spinal anesthetic, she developed a complete left-sided sensory and motor block, with no block on the right. A supplemental epidural catheter was placed and lidocaine 2%, 12 cc with fentanyl 100 micrograms was used, which successfully achieved bilateral surgical anesthesia. The remainder of the case and postoperative course were unremarkable. This case illustrates the possibility of a structurally confined subarachnoid space leading to true one-sided spinal anesthesia. Prompt recognition and epidural rescue preserved patient comfort and surgical conditions. Anatomic factors should be considered when assessing neuraxial block failures, particularly in patients with prior spinal procedures.