A 70-year-old man is admitted to ICU with septic shock. He receives 30 mL/kg of Hartmann's solution (2.1 L) as part of initial resuscitation. After 6 hours, he remains hypotensive (MAP 58 mmHg) despite noradrenaline. The registrar proposes a further 500 mL fluid bolus. Dynamic assessment shows a pulse pressure variation (PPV) of 6% on controlled mechanical ventilation (TV 8 mL/kg, sinus rhythm). What does the PPV suggest?