A 63-year-old man is brought to the emergency department with fever, rigours, and confusion. Blood pressure is 84/50 mm Hg, heart rate 120 beats per minute, respiratory rate 28 breaths per minute, oxygen saturation 93 percent on room air, and lactate 4.2 mmol per litre. Sepsis with septic shock is suspected. According to the 2021 Surviving Sepsis Campaign guidelines, what is the most appropriate initial fluid resuscitation strategy?