A 35-year-old male patient is scheduled for emergency laparotomy for acute abdomen. Induction is with propofol and fentanyl. During intubation, succinylcholine 1.5 mg/kg IV is administered. Within 30 seconds of drug administration, the patient develops severe muscle rigidity, trismus, and masseter muscle spasm. Core temperature begins to rise. What is the most appropriate immediate management?