A 28-year-old male from rural Maharashtra is scheduled for emergency appendicectomy under general anesthesia. Induction is uneventful with propofol and succinylcholine. Within 2 minutes of intubation, the anesthetist notices the jaw muscles are rigid and the patient's core temperature begins to rise. Capnography shows a steep rise in end-tidal CO₂ (ETCO₂) from 35 to 65 mmHg within 5 minutes. Arterial blood gas shows pH 7.15, PaCO₂ 85 mmHg, and K⁺ 6.8 mEq/L. What is the most appropriate immediate management?