8.4 Oncologic Emergencies: Tumor Lysis Syndrome, Bleeding Masses & Hypercalcemia

Oncologic Emergencies: Tumor Lysis Syndrome, Bleeding Masses & Hypercalcemia

Veterinary oncology patients frequently present to the emergency department with acute, life-threatening crises resulting directly from tumor burden, vascular invasion, paraneoplastic humoral syndromes, or cytotoxic therapy. Advanced veterinary nurses must rapidly recognize and stabilize three major oncologic emergencies: Acute Tumor Lysis Syndrome (TLS), Acute Hemoperitoneum from Bleeding Masses, and Humoral Hypercalcemia of Malignancy (HHM).

1. Acute Tumor Lysis Syndrome (TLS)

Tumor Lysis Syndrome (TLS) is an acute, life-threatening metabolic oncologic emergency caused by the rapid, massive lysis of neoplastic cells and the sudden dumping of intracellular contents into the systemic circulation. It classically develops 12 to 48 hours following induction chemotherapy (e.g., CHOP protocol for high-grade lymphoma, acute lymphoblastic leukemia, or large bulky solid tumors), but can occasionally occur spontaneously.

[Tumor Lysis Syndrome Metabolic Quartet]
                   Massive Lysis of Neoplastic Cells
                                  │
         ┌────────────────────────┼────────────────────────┐
         ▼                        ▼                        ▼
  [HYPERKALEMIA]          [HYPERPHOSPHATEMIA]      [PURINE RELEASE / URIC ACID]
  • Intracellular K+      • Intracellular Phos     • Nucleic acid catabolism
    floods circulation      4x higher in lymphs    • Hyperuricemia & Urate Crystals
  • Cardiotoxicity        • Binds Ionized Calcium  • Acute Renal Tubular Obstruction
  • Lethal Bradycardia,   • Calcium-Phosphate      • Severe Metabolic Acidosis
    Spiked T-Waves,         Precipitation (Ca x P >60)
    Vtach / Asystole              │
                                  ▼
                        [SECONDARY HYPOCALCEMIA]
                        • Tetany, Muscle Tremors
                        • Facial Rubbing, Seizures
                        • Prolonged QT Interval

The Classic Electrolyte & Metabolic Alterations

1. Severe Hyperkalemia ($K^+ > 6.5\text{–}8.0\text{ mEq/L}$): Massive release of intracellular potassium. Produces severe cardiotoxicity: tall tented T-waves, widened QRS complexes, loss of P-waves, sine-wave rhythms, ventricular fibrillation, and asystolic cardiac arrest.
2. Severe Hyperphosphatemia ($P > 10\text{–}14\text{ mg/dL}$): Neoplastic lymphoblasts contain up to 4 times the intracellular phosphorus concentration of mature lymphocytes. Rapid phosphate release overwhelms renal excretory capacity.
3. Secondary Hypocalcemia ($i\text{Ca}^{2+} < 0.8\text{ mmol/L}$): Excess serum phosphate binds ionized calcium, forming insoluble calcium phosphate crystals that deposit in renal tubules and soft tissues when the Calcium $\times$ Phosphorus product exceeds $60\text{–}70\text{ mg}^2/\text{dL}^2$. Causes neuromuscular hyperexcitability, tetanic muscle spasms, facial pruritus, and seizures.
4. Acute Kidney Injury (AKI) & Uremic Metabolic Acidosis: Precipitated by acute calcium phosphate nephrocalcinosis, hyperuricemic nephropathy, and renal tubular obstruction.

Emergency Management & Prevention of TLS

• Aggressive IV Isotonic Crystalloid Diuresis: Administer 0.9% NaCl or balanced crystalloids at $2\text{–}3\times$ maintenance ($6\text{–}9\text{ mL/kg/hr}$) starting 12–24 hours prior to chemotherapy and continuing for 48 hours post-treatment to maximize glomerular filtration and urine flow.
• Cardioprotective Calcium Gluconate: If hyperkalemic ECG abnormalities are present, administer 10% Calcium Gluconate ($0.5\text{–}1.0\text{ mL/kg IV slow over 10–15 min}$) with continuous ECG monitoring. (Stabilizes myocardial resting membrane potential without lowering serum potassium).
• Potassium-Lowering Pharmacotherapy:
  • Regular Insulin ($0.25\text{–}0.5\text{ U/kg IV}$) combined with $2.0\text{ g Dextrose per Unit of insulin IV}$ (shifts $K^+$ intracellularly via $Na^+/K^+$-ATPase activation).
  • Nebulized Albuterol ($0.05\text{ mg/kg}$) (beta-2 agonist shifting potassium intracellularly).
• Phosphate Binders & Uric Acid Modulators: Aluminum hydroxide ($30\text{–}50\text{ mg/kg/day PO}$) to bind enteric phosphorus; Allopurinol or Rasburicase to blunt uric acid crystalluria.

2. Hemoperitoneum from Bleeding Masses & Emergency Autotransfusion

Spontaneous, non-traumatic hemoperitoneum is a common presenting complaint in older large-breed dogs. The most common underlying etiology is a ruptured splenic tumor (Splenic Hemangiosarcoma [HSA] accounting for ~2/3 of all splenic malignancies, versus benign splenic hematomas, followed by ruptured hepatic, retroperitoneal, or adrenal masses).

Triage & Point-of-Care Diagnostics

1. AFAST (Abdominal FAST) Ultrasound: Rapidly identifies anechoic fluid in the cysto-colic, spleno-renal, hepato-renal, and diaphragmatico-hepatic acoustic windows.
2. Diagnostic Abdominocentesis & PCV/TS Comparison:
   • Aspirate fluid using a 20G–22G needle or catheter.
   • The PCV Hallmark: In acute hemoperitoneum, the effusion PCV is typically equal to or higher than the peripheral blood PCV (often 10–20% higher due to splenic erythrocyte concentration).
   • The Clotting Test: True cavitary hemoperitoneum fails to clot in a plain glass/plastic tube (red-top) because peritoneal mesothelial cells rapidly defibrinogenate shed blood. If aspirated blood forms a firm clot, accidental iatrogenic vessel or organ puncture must be suspected.

Damage Control Resuscitation: Permissive Hypotension

In active, uncontrolled intra-abdominal hemorrhage, aggressive crystalloid boluses to achieve normal blood pressures dislodge newly formed, fragile platelet/fibrin plugs ("popping the clot") and dilute clotting factors.

• Target Endpoints: Maintain permissive hypotension (Target MAP $50\text{–}60\text{ mmHg}$ or SBP $80\text{–}90\text{ mmHg}$, palpably restored peripheral pulses, and mentation improvement) using small aliquots of balanced crystalloids ($10\text{–}15\text{ mL/kg}$) or hypertonic saline ($4\text{ mL/kg}$), while preparing for definitive surgical hemostasis.

Emergency Autotransfusion Protocols

When homologous donor blood products are unavailable and an exsanguinating patient faces imminent cardiac arrest, autotransfusion of cavity-shed blood can be lifesaving.

• Technique: Peritoneal blood is aseptically aspirated into large syringes or a sterile suction canister. The blood is then re-infused into the patient's intravenous line through a standard 170–260 micron blood filter (or a 40-micron microaggregate filter).
• Anticoagulant Requirement: Because shed intra-abdominal blood has already undergone mesothelial defibrinogenation, anticoagulant (ACD-A or citrate) is generally not required during collection, though some protocols add 1 mL ACD-A per 7–10 mL blood if rapid clotting is feared.
• Contraindications & Complications:
  • Absolute Contraindication: Bacterial contamination (concurrent GI perforation, septic peritonitis) or gross urine/bile leakage.
  • Relative Caution in Neoplasia: Risk of re-infusing neoplastic cells (e.g., HSA cells). However, autotransfusion remains strictly indicated when the alternative is immediate fatal hemorrhagic shock.

3. Paraneoplastic Hypercalcemia (Humoral Hypercalcemia of Malignancy - HHM)

Hypercalcemia is the most common paraneoplastic syndrome in veterinary medicine, accounting for 60% to 70% of all hypercalcemic canine cases. Humoral Hypercalcemia of Malignancy (HHM) is mediated by tumor secretion of Parathyroid Hormone-related Protein (PTHrP).

[Humoral Hypercalcemia of Malignancy Pathophysiology]
                 Neoplasm Secretes PTHrP (Lymphoma / AGASACA)
                                  │
         ┌────────────────────────┴────────────────────────┐
         ▼                                                 ▼
  [BONE RESORPTION]                              [RENAL REABSORPTION]
  • Activates Osteoclasts                        • Binds renal PTH receptors
  • Massive mobilization of                      • Maximizes tubular Ca2+ reabsorption
    Calcium & Phosphorus into blood              • Inhibits Aquaporin-2 & ADH (Nephrogenic DI)
         │                                                 │
         └────────────────────────┬────────────────────────┘
                                  ▼
                 [SEVERE IONIZED HYPERCALCEMIA]
                 • Polyuria / Polydipsia (PU/PD)
                 • Acute Renal Vasoconstriction & Ischemia
                 • Nephrocalcinosis -> Irreversible AKI
                 • Bradycardia, Shortened QT Interval

Underlying Malignancies

1. Canine Lymphoma: Particularly T-cell lymphoma (~40% of hypercalcemic dogs).
2. Apocrine Gland Anal Sac Adenocarcinoma (AGASACA): Highly associated with severe PTHrP secretion (always perform a digital rectal examination on all sick dogs!).
3. Multiple Myeloma: Localized osteoclast-activating factors and bone resorption.
4. Carcinomas: Mammary, lung, and thyroid carcinomas.

Clinical Manifestations of Ionized Calcium Toxicity

Total serum calcium can be misleading due to fluctuations in albumin; ionized calcium ($i\text{Ca}^{2+}$; normal: $1.15\text{–}1.35\text{ mmol/L}$) reflects true physiological toxicity:

• Renal Signs (Nephrogenic Diabetes Insipidus): Severe PU/PD. Hypercalcemia blocks antidiuretic hormone (ADH) signaling on aquaporin-2 channels in the renal collecting ducts, causing profound hyposthenuric polyuria.
• Cardiovascular Signs: Bradycardia, shortened QT interval, ventricular arrhythmias, and systemic arterial hypertension.
• Gastrointestinal & Neurological Signs: Anorexia, vomiting, severe constipation (decreased smooth muscle excitability), muscle weakness, tremors, and stupor.
• Calcium $\times$ Phosphorus Danger: When the total serum $[\text{Ca}] \times [\text{P}]$ product exceeds $60\text{–}70\text{ mg}^2/\text{dL}^2$, metastatic mineral precipitation into renal basolateral membranes causes acute irreversible tubulointerstitial nephrocalcinosis and fatal anuric renal failure.

Emergency Multi-Tier Medical Management