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A 51-year-old man is being followed in the hospital after receiving chemotherapy for acute myeloid leukemia 1 day ago. Kidney function was normal at the start of his treatment, which consisted of normal saline at a rate of 200 mL/h and rasburicase on the day of chemotherapy. He reports no symptoms except for some fatigue and nausea. He has no shortness of breath or fever.

On physical examination, the patient is afebrile. Blood pressure is 122/70 mm Hg, pulse rate is 72/min, and respiration rate is 12/min. BMI is 25. Some bruising is noted on the skin. There is no jugular venous distention. Heart rate is regular. Lungs are clear to auscultation. There is no edema.

Urine output has been around 50 mL/h.

Laboratory studies:

Albumin	3.2 g/dL (32 g/L)
Blood urea nitrogen	14 mg/dL (5.0 mmol/L)
Calcium	9 mg/dL (2.3 mmol/L)
Serum creatinine	1.0 mg/dL (88.4 µmol/L) (baseline: 0.9 mg/dL [79.6 µmol/L])
Electrolytes
Sodium	139 mEq/L (139 mmol/L)
Potassium	5.2 mEq/L (5.2 mmol/L)
Chloride	100 mEq/L (100 mmol/L)
Bicarbonate	25 mEq/L (25 mmol/L)
Phosphorus	5.7 mg/dL (1.84 mmol/L)
Uric acid	7.1 mg/dL (0.42 mmol/L)

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

A: Add sodium bicarbonate to intravenous fluid at current rate
B: Add sodium polystyrene sulfonate
C: Increase intravenous saline rate
D: Substitute allopurinol for rasburicase

MKSAP Answer and Critique

The correct answer is C: Increase intravenous saline rate. This item is available to MKSAP 16 subscribers as item 3 in the Nephrology section.

An increase in the intravenous saline rate is appropriate. This patient with acute myeloid leukemia received chemotherapy 1 day ago and is at risk for tumor lysis syndrome. Manifestations include acute kidney injury and arrhythmias resulting from the release of potassium, phosphorus, and uric acid from cells. The cell death can be spontaneous with highly proliferative malignancies but more commonly is induced by chemotherapy. Patients with untreated tumor lysis syndrome present with hyperkalemia, hyperuricemia, and hyperphosphatemia. Optimal treatment to prevent tumor lysis syndrome is intravenous fluids to promote a faster urine flow rate. The goal intravenous fluid rate is up to 3000 mL/m²/d, around 6 L/d in this patient. Although his initial intravenous fluid rate was reasonable, his high phosphorus and potassium levels suggest that cell breakdown is occurring, and an increased rate of saline infusion will help promote potassium excretion and decrease the solubility of phosphorus and uric acid by increasing urine volume. In this patient, an increased intravenous fluid with normal saline at a rate of 250 mL/h would be appropriate. The use of a loop diuretic to maintain urine flow is also reasonable in selected patients.

Although intravenous fluid with sodium bicarbonate has the benefit of alkalinizing the urine and therefore increasing uric acid clearance, it also increases the risk of calcium phosphorus precipitation, which can increase damage to the kidneys, and is not appropriate for this patient with a high serum phosphorus level.

Sodium polystyrene sulfonate can be used to treat this patient’s hyperkalemia but will not improve his urine flow.

Rasburicase is generally preferred to allopurinol for prophylaxis of tumor lysis syndrome because of differences in mechanism. Rasburicase directly breaks down uric acid and minimizes xanthine accumulation, whereas allopurinol does not. Because this patient’s serum uric acid levels appear to be adequately controlled with rasburicase, there would be no benefit of treatment with allopurinol.

Key Point

• Optimal treatment to prevent tumor lysis syndrome is intravenous fluids to promote a faster urine flow rate.

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