A 68-year-old man presents to the emergency department with fever, productive cough and pleuritic chest pain for 3 days. He has confusion and a respiratory rate of 32 breaths per minute; blood pressure is 86/52 mm Hg, lactate 4.2 mmol/L. You suspect septic shock from community-acquired pneumonia. According to the Surviving Sepsis Campaign recommendations, what is the most important initial management step within the first hour?