tokens: Anesthesia was induced by droperidol 0 . 2 mg . kg - 1 , fentanyl 50 micrograms , thiamylal 150 - 250 mg , and succinylcholine 1 mg . kg - 1 , and maintained with nitrous oxide and O2 ( 67 : 33 ) supplemented with repeated i . v . doses of fentanyl ( within 15 micrograms . kg - 1 ) .