A 28-year-old woman with severe sepsis secondary to pneumonia presents to the ICU with fever (39.8°C), tachycardia (HR 118/min), and tachypnea (RR 28/min). Arterial blood gas shows pH 7.32, PaCO₂ 32 mmHg, HCO₃⁻ 16 mEq/L, PaO₂ 78 mmHg on FiO₂ 0.40. Lactate is elevated at 4.2 mmol/L. Despite adequate oxygenation targets (SpO₂ 94%), tissue oxygen delivery remains compromised. Which of the following is the most appropriate immediate next step in management?