Soru

A $61$-year-old woman is brought to the emergency department by her husband due to progressive weakness and severe diarrhea. She has a history of metastatic melanoma and began combination immunotherapy with ipilimumab and nivolumab four weeks ago. Over the past three days, she has had up to eight large-volume, watery bowel movements daily, accompanied by diffuse abdominal cramping. Over the last $12$ hours, she has also developed new-onset palpitations, a sensation of a 'racing heart,' and mild shortness of breath at rest.

Her temperature is $37.8^\circ\text{C}$ ($100.0^\circ\text{F}$), blood pressure is $105/65\text{ mmHg}$, pulse is $118\text{/min}$ and irregular, and respiratory rate is $20\text{/min}$. Oxygen saturation is $96\%$ on room air. Physical examination reveals dry mucous membranes and diffuse, mild abdominal tenderness without guarding or rebound. Cardiovascular examination reveals an irregular rhythm with no murmurs, rubs, or gallops.

Which of the following are the most appropriate diagnostic and monitoring steps in the evaluation of this patient? (Select all that apply)