a 28 year old woman presents to er with a fever of 102.1f, shaking chills and flank pain. her urine culture reveals pan-sensitive e. coli (organism is sensitive to every available antibiotic). she is admitted to the hospital and started on iv (intravenous) zosyn (piperacillin/tazobactam). she continues to deteriorate clinically 48 hours after the initiation of antibiotics and appropriate fluid resuscitation with increasing heart rate, decreasing blood pressure, and is becoming more confused. the next most appropriate step is: