A 48-year-old woman on ICU develops acute cholangitis with Charcot's triad (fever, jaundice, right upper quadrant pain). USS shows CBD dilatation with stones. She is started on IV piperacillin/tazobactam. Despite 24 hours of antibiotics and fluid resuscitation, she develops Reynolds' pentad (Charcot's triad + confusion + hypotension). What is the most important intervention?