A 72-year-old man presents to the emergency department with fever, productive cough and confusion. His observations are: temperature 39.2°C, blood pressure 88/54 mmHg, heart rate 124 bpm, respiratory rate 30/min, oxygen saturation 90% on air. You suspect sepsis secondary to pneumonia and his NEWS2 score is 9. Which single action should be prioritised and completed within the first hour of recognition?