A 45-year-old woman presents with fever, severe RUQ pain, and jaundice for the past 24 hours. She has a history of gallstones and has experienced similar, less severe pain episodes in the past. On examination, she appears ill and has a temperature of 38.9°C (102°F). Laboratory tests show leukocytosis, elevated bilirubin, and markedly elevated alkaline phosphatase. What is the most appropriate initial step in the management of this patient?
