A 72-year-old man presents with acute severe chest pain and haemodynamic collapse. ECG shows ST elevation in leads II, III, and aVF. He is intubated due to cardiogenic shock. Echocardiography shows severe RV dilatation with RV free wall akinesis and preserved RV apical contraction (McConnell's sign), with a small underfilled LV. MAP is 52 mmHg. What is the most appropriate initial fluid management strategy?