Pitfall of bispectral index during intraoperative seizure -a case report-
A 42-year-old male patient with chronic renal failure underwent emergency kidney transplantation. The patient had undergone kidney transplantation 15 years previously, but graft failure had occurred 7 years previously. Ever since then, the patient had been on hemodialysis. Preoperative laboratory findings showed serum sodium 126 mmol/L with uric acid 5.9 mg/dl. The patient had no medical history of epilepsy.\nAnesthesia was induced with propofol 100 mg, fentanyl 100 µg, and atracurium 25 mg. After tracheal intubation, ventilation was controlled to keep end-tidal CO2 (ETCO2) maintained around 35 mmHg. Monitors included invasive right radial arterial blood pressure, central venous pressure through right internal jugular vein, pulse oximetry, electrocardiography, peripheral nerve stimulation applying train-of-four stimulation, body temperature using esophageal temperature probe, and bispectral index (BisVISTA, Aspect Medical Systems, Newton, MA, USA). Anesthesia was maintained with desflurane 5-6% based on hemodynamic measurements and BIS values, O2 with Air (1 : 1, FiO2 60%), and muscle relaxation was achieved by using atracurium. Fluid replacement was done with 0.45% saline.\nThe BIS value dropped to 40 following the induction sequences and was stably maintained 40-50 afterward. About 4 hours after the beginning of surgery, when surgery was almost over and surgeons were closing fascia, generalized tremor occurred along with deviation of the eyeballs to the right upper side. At that time the BIS value increased from 40 to a peak value of 62, and then was maintained mainly in the 50s during the seizure. After the tremor, a sudden and brief fall of BIS values were noticed. The BIS value dropped from 50 to 0 within a minute, stayed at 0 for about 5 minutes, and then returned to 50 without significant hemodynamic change (). During these sudden changes, signal quality index stayed over 80 with no other error messages. Arterial blood gas analysis was done immediately, which showed serum sodium level of 122 mmol/L. In order to correct hyponatremia, 0.45% saline was replaced with 0.9% saline. Neuromuscular blockade was not sufficiently maintained, which was below 75%, since we were preparing for emergence concerning the time remaining in the surgery. When tremor occurred, an additional dose of atracurium 10 mg was injected to stop muscle contraction. Although the generalized tremor faded, such a brief fall of BIS occurred periodically for the next 30 minutes, after which the BIS value stabilized and stayed around 40 and the patient emerged without any problem. At emergence, the patient's mental status was clear enough to allow recall of his own name.\nThe patient was transferred to intensive care unit (ICU) right after emergence. Fifteen minutes from emergence, the patient had a generalized tonic-clonic seizure lasting 10 minutes, followed by three more episodes, each lasting 5 minutes, every 30 minutes. The patient's laboratory findings when having seizure were uric acid 13.1 mg/dl and serum sodium 124 mmol/L. The patient was immediately referred for consultation to staff neurologists. An electroencephalography (EEG) performed in postictal period showed brief and generalized 5-7 Hz theta slowing waves indicative of mild cortical dysfunction caused by metabolic disturbance, toxic state, interictal state or postictal state. Intravenous lorazepam 4 mg was used and O2 3 L/min was supplied by nasal cannula. The consulting neurologists diagnosed seizure by metabolic disturbance and prescribed intravenous fosphenytoin 150 mg every 8 hours and intravenous sodium valproate 300 mg every 12 hours. No further seizures occurred, but patient displayed a confused mental state for 10 days before normalizing. Serum sodium and uric acid normalized 2 days after surgery. Antiepileptic drugs were continued for 3 days.