A 58-year-old man presents with fever, rigours and confusion. Vitals: BP 82/50 mmHg, HR 120/min, RR 28/min, T 39.0 °C, oxygen saturation 93% on room air. Lactate is 4.5 mmol/L. According to the 2021 Surviving Sepsis Campaign guideline, what is the MOST appropriate initial fluid resuscitation strategy?