A 76-year-old woman fails to emerge from a debulking laparotomy for ovarian cancer. The anesthetic was conducted under general and epidural anesthesia, with a T10-11 catheter. The patient has no cranial nerve reflexes, with dilated & nonreactive pupils, 45 minutes after cessation of inhaled and intravenous anesthetic agents. Serum glucose is normal. The patient was administered 10 cc 0.25% bupivacaine with skin closure. What is the MOST likely etiology?

A) Residual cisatracurium neuromuscular blockade
B) High epidural spread of local anesthetic to the skull base
C) Inadvertent intrathecal local anesthetic administration (i.e., "high spinal")
D) Excessive opioid administration