Soru

An elderly man is admitted due to a two-week history of worsening dyspnea, orthopnea, and increasing lower extremity edema. His past medical history is significant for ischemic cardiomyopathy with a left ventricular ejection fraction of $30\%$. To manage his fluid overload at home, he recently doubled his daily dose of oral torsemide independently.

Upon admission, his blood pressure is $92/58\text{ mmHg}$, pulse is $108/\text{min}$, and respiratory rate is $22/\text{min}$. Jugular venous pressure is visibly elevated. Lung auscultation reveals bilateral basilar crackles, and a third heart sound (S3) is present on cardiac exam.

Laboratory evaluation yields the following results:
Serum chemistry:
Sodium: $132\text{ mEq/L}$
Potassium: $3.1\text{ mEq/L}$
Chloride: $94\text{ mEq/L}$
Bicarbonate: $29\text{ mEq/L}$
Blood urea nitrogen (BUN): $75\text{ mg/dL}$
Creatinine: $2.5\text{ mg/dL}$ (baseline $1.2\text{ mg/dL}$)

Spot urine chemistry:
Sodium: $66\text{ mEq/L}$
Urea nitrogen: $450\text{ mg/dL}$
Creatinine: $60\text{ mg/dL}$

To evaluate the etiology of the acute kidney injury in the setting of recent loop diuretic use, the medical team decides to calculate a specific fractional excretion index that is less confounded by his medication regimen than sodium excretion.

What is the calculated value of this preferred index, expressed as a percentage?