Tumor Lysis, Hypercalcemia, SIADH, and Metabolic Emergencies
Key Takeaways
- Tumor lysis syndrome (TLS) produces hyperkalemia, hyperphosphatemia, hyperuricemia, and secondary hypocalcemia with acute kidney injury, and is most common with bulky, highly proliferative tumors such as Burkitt lymphoma and acute leukemias.
- Rasburicase rapidly lowers uric acid but is contraindicated in G6PD deficiency because it can cause severe hemolysis and methemoglobinemia.
- Hypercalcemia of malignancy is graded by corrected serum calcium: mild below 12 mg/dL, moderate 12 to 14 mg/dL, and severe above 14 mg/dL; aggressive isotonic saline is first-line therapy.
- SIADH causes euvolemic dilutional hyponatremia; sodium must be corrected slowly (no more than about 8 mEq/L in 24 hours) to avoid osmotic demyelination.
- Compare current labs against baseline and rate of change rather than judging a single value, because a rapidly rising potassium can be deadlier than a stable mild elevation.
Tumor Lysis, Hypercalcemia, SIADH, and Metabolic Emergencies
Metabolic emergencies are heavily tested because they reward fast recognition and disciplined monitoring. Early symptoms look nonspecific: fatigue, nausea, poor intake, constipation, muscle cramps, headache, confusion, or falling urine output. The skilled RN connects these findings to diagnosis, treatment timing, renal function, hydration, and recent laboratory values.
Tumor Lysis Syndrome
Tumor lysis syndrome (TLS) occurs when malignant cells break down rapidly and dump intracellular contents into the blood. It is most associated with acute leukemias, Burkitt and other high-grade lymphomas, bulky disease, high white counts, high chemosensitivity, and pre-existing renal impairment, typically 12 to 72 hours after starting cytotoxic therapy (occasionally spontaneously before treatment).
| Lab change | Direction | Nursing concern |
|---|---|---|
| Potassium | High | Dysrhythmia, cardiac arrest, peaked T waves |
| Phosphorus | High | Binds calcium; renal injury |
| Calcium | Low (secondary) | Tetany, seizures, prolonged QT, cramps |
| Uric acid | High | Crystal nephropathy, acute kidney injury |
| Creatinine | Rising | Falling clearance worsens every value above |
Prevention and management include aggressive IV hydration, strict intake and output, daily weights, telemetry for high-risk patients, and frequent labs. Allopurinol blocks new uric acid formation, while rasburicase enzymatically degrades existing uric acid for high-risk patients. A high-stakes safety point: rasburicase is contraindicated in glucose-6-phosphate dehydrogenase (G6PD) deficiency because it precipitates hemolysis and methemoglobinemia. Do not give calcium for asymptomatic hypocalcemia in TLS unless directed - calcium-phosphate precipitation can worsen renal injury.
Hypercalcemia of Malignancy
Hypercalcemia is the most common metabolic emergency in cancer. Mechanisms include tumor secretion of parathyroid hormone-related peptide (PTHrP) (most cases, often squamous cell cancers), osteolytic bone metastases, and myeloma. Always use the corrected calcium for low albumin: add 0.8 mg/dL to the measured calcium for every 1.0 g/dL the albumin is below 4.0 g/dL. Severity grading drives urgency:
| Corrected calcium | Severity | Typical action |
|---|---|---|
| Below 12 mg/dL | Mild | Hydration, treat the malignancy |
| 12 to 14 mg/dL | Moderate | IV saline; bisphosphonate |
| Above 14 mg/dL | Severe | Aggressive saline, calcitonin, admit |
Classic symptoms follow the mnemonic "stones, bones, groans, thrones, and psychiatric overtones": kidney stones, bone pain, abdominal groans (constipation, nausea), polyuria (thrones), and confusion. The electrocardiogram shows a shortened QT interval. First-line therapy is aggressive isotonic saline to restore volume; calcitonin lowers calcium within hours as a bridge, and a bisphosphonate (zoledronic acid) or denosumab gives durable control over 2 to 4 days. Monitor for fluid overload in cardiac or renal patients, and never use loop diuretics until the patient is volume-replete.
SIADH and Hyponatremia
Syndrome of inappropriate antidiuretic hormone (SIADH) causes water retention and euvolemic, dilutional hyponatremia, classically with small cell lung cancer but also CNS disease, certain drugs (vincristine, cyclophosphamide, cisplatin), pain, and nausea. Labs show low serum sodium and serum osmolality with inappropriately concentrated urine (high urine sodium and osmolality). Symptoms track the sodium level and its speed of fall: headache, nausea, and cramps early; seizures, coma, and respiratory arrest with severe or rapid drops.
- Implement seizure and fall precautions, frequent neuro checks, strict intake and output, and daily weights.
- Apply fluid restriction only as ordered (often 800 to 1000 mL/day) and explain it clearly, since thirsty or confused patients undermine it.
- Hypertonic (3%) saline is reserved for severe symptomatic hyponatremia; vasopressin antagonists (vaptans) may be used.
- Correct sodium slowly - no more than about 8 mEq/L in 24 hours. Overly rapid correction risks osmotic demyelination syndrome (central pontine myelinolysis), a devastating, often irreversible neurologic injury. Never encourage unsupervised salt loading.
Escalation, Education, and Monitoring Patterns
Escalate urgently for seizure, new confusion, severe weakness, tetany, chest pain, palpitations, syncope, oliguria, or marked lab abnormalities. Use teach-back so high-risk patients know why labs are checked frequently, why hydration and urine measurement matter, and exactly which number to call. The core monitoring discipline is to trend against baseline and rate of change: a potassium still within range but climbing fast is more dangerous than a stable mild elevation, and for SIADH a new neurologic change is the warning that the sodium is now affecting the brain.
Worked Examples and Handoff
Work an example for each syndrome. In TLS, a patient with bulky Burkitt lymphoma starting chemotherapy reports muscle twitching, and labs show potassium 6.2, phosphorus 7.5, calcium 7.0, uric acid 11, and creatinine rising from 0.9 to 1.6. This is full-blown TLS - escalate, place on telemetry for the hyperkalemia, hold any potassium-containing fluids, anticipate rasburicase, and do not push calcium for the asymptomatic hypocalcemia.
In hypercalcemia, an older adult with breast cancer presents with confusion, constipation, and a corrected calcium of 14.5; this severe level needs aggressive isotonic saline, calcitonin as a bridge, and a bisphosphonate, with fall precautions for the altered mentation. In SIADH, a small cell lung cancer patient with a sodium of 116 and a new headache needs seizure precautions, ordered fluid restriction, and slow correction.
Handoff for any metabolic emergency should include the suspected syndrome, the most recent labs with their rate of change, fluids or fluid restriction ordered, medications given, telemetry and seizure-precaution status, and the family teaching completed. The recurring exam theme is that the nurse who trends values and links them to the diagnosis and treatment timing catches these emergencies before the patient codes, seizes, or goes into renal failure.
Which laboratory pattern is most consistent with tumor lysis syndrome?
A nurse is reviewing orders for a patient at high risk for TLS. Which order requires clarification before administration?
A patient with small cell lung cancer has a serum sodium of 118 mEq/L. The nurse should question which order?