A 70-year-old man is brought to the emergency department with confusion, fever 102.4 F, and hypotension. Blood pressure is 84/52 mm Hg, heart rate 118 per minute, respiratory rate 26 per minute, oxygen saturation 93 percent on room air. Lactate is 4.2 mmol per L. Suspected source is pneumonia. According to current sepsis guidelines, what is the most appropriate initial fluid resuscitation strategy?