A 52-year-old man develops septic shock 24 hours after an emergency Hartmann's procedure for sigmoid perforation. He is on noradrenaline 0.5 mcg/kg/min and vasopressin 0.03 units/min. MAP is 60 mmHg. Lactate is 6.0 mmol/L. CT abdomen shows a residual pelvic collection. What is the most important management priority?