A 58-year-old man with a history of hypertension (BP 180/110 mmHg) presents to the emergency department with acute onset severe headache, neck stiffness, and vomiting. CT head (non-contrast) shows a 4 cm left basal ganglia hemorrhage with intraventricular extension and mild hydrocephalus. GCS is 13. What is the most appropriate immediate next step in management?