A 70-year-old man presents to the emergency department with fever, rigors, hypotension (BP 86/50 mmHg), tachycardia (HR 118 beats/min) and tachypnoea (RR 26 breaths/min). He is confused and has warm peripheries. Suspected source is pneumonia. According to the Australian Sepsis Clinical Care Standard, which action is the highest priority within the first hour?