Question

While rounding in the surgical intensive care unit, a physician is urgently called to the bedside of a 68-year-old male patient who abruptly developed respiratory distress. The patient underwent a right hemicolectomy for stage III colon cancer two days ago. Two hours prior to the acute event, his hemoglobin level was noted to be $6.8$ g/dL, prompting the initiation of a cross-matched packed red blood cell transfusion. Approximately $30$ minutes after the transfusion began, the patient reported the sudden onset of shaking chills and severe pain in his right flank.

Vital signs reveal a temperature of $39.2^\circ\text{C}$ ($102.6^\circ\text{F}$), heart rate of $122/\text{min}$, blood pressure of $85/50$ mm Hg, and respiratory rate of $24/\text{min}$. Pulse oximetry shows an oxygen saturation of $94\%$ on room air.

Physical examination shows profound diaphoresis and anxiety. Jugular venous pulsations are not elevated. Auscultation of the chest reveals clear breath sounds in all lung fields. The surgical incision is intact without erythema or purulent drainage. Inspection of the Foley catheter drainage system reveals that the previously clear, yellow urine has acutely transitioned to a dark, reddish-brown color.

Which of the following is the most appropriate initial step in management?