ONCOLOGY

Neoplastic disease in children usually involves the hematopoietic system, the CNS and sympathetic nervous system, and soft tissue, bone, and kidney. Although much of oncology has become an outpatient subspecialty, some clinical situations do require hospitalization and intensive care.

Blast Crisis in Leukemia

Children with an initial white blood cell (WBC) count of more than 100,000 are at a high risk for two potentially lethal complications: leukostasis and metabolic crisis (tumor lysis syndrome).

Leukostasis

Leukostasis is a syndrome of vascular obstruction caused by the high viscosity of elevated cell counts or by the WBCs themselves. This syndrome should be anticipated in acute lymphoblastic leukemia patients with WBC counts of more than 500,000 and in AML patients with WBC counts of more than 200,000. The leukemic cell in AML is less deformable than the lymphoblast; therefore, in AML, a relatively lower WBC count can produce the same syndrome.^[325]

The two major target organs for leukostasis are the brain and the lung; the pathophysiologic feature is vascular plugging causing an infarct. The initial symptoms include tachypnea, cyanosis, increased work of breathing, altered mental status, and focal neurologic deficits. In addition to supportive therapy, the goal is to decrease the circulating tumor load and thereby decrease viscosity. Leukapheresis and exchange transfusion transiently lower the tumor mass. Cranial radiation may reduce the CNS load, and chemotherapy interrupts cell production and possibly destroys circulating cells. The initial chemotherapy is aimed at stopping cell production without a large amount of cell lysis; such treatment gives the advantage of halting a continually growing tumor load without causing a huge metabolic crisis before adequate perfusion is reestablished.^{[326] [327] [328]}

Tumor Lysis Syndrome

Tumor lysis syndrome is a metabolic crisis precipitated by acute lysis of a large tumor load. The main abnormalities that result are elevations in uric acid, potassium, and phosphate; the elevated phosphate results in hypocalcemia. The hyperkalemia and hypocalcemia can be life

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Specific therapy is anticipatory monitoring with alkalinization of the urine and diuresis. Before any chemotherapy is administered, the patient's renal function should be assessed and allopurinol therapy begun. In most cases, this conservative approach of forced diuresis and allopurinol is adequate, but occasionally, dialysis must be instituted. Indications for the initiation of dialysis include the following:

1. Potassium >6 mEq/L and rising despite resin exchange
2. Uric acid >19 mg/L
3. Creatinine >10 mg/L
4. Phosphorus >10 mg/L or rapidly rising
5. Volume overload
6. Symptomatic hypocalcemia

If dialysis is necessary, it is usually needed for only a few days until tumor lysis is nearly complete.