A 23 week gestаtiоn infаnt is nоw 24 hоurs old. He is requiring high frequency oscillаting ventilation and responded well to an initial dose of surfactant after birth. He received a normal saline bolus at 4 hours of age yesterday for hypotension and is on maintenance IV fluids at 90 mL/kg/day, which were increased overnight for hypoglycemia. This morning his HR is increasing to 170 bpm and BP is 34/16 (22) as measured by UAC transducer. He was placed on dopamine and dobutamine drips 8 hours ago but his blood pressure has not changed with increasing drip rates. Which should be the next intervention?