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 anesthesiologist notices the patient's jaw is rigid and muscles are tense. Core temperature rises from 36.8°C to 38.2°C within 5 minutes. Capnography shows a sudden rise in end-tidal CO₂ from 35 to 55 mmHg. Arterial blood gas reveals pH 7.28, PaCO₂ 62 mmHg, HCO₃⁻ 28 mEq/L, and K⁺ 6.2 mEq/L. Urine output is minimal and dark-colored. What is the most appropriate immediate management?