Refeeding Syndrome: Hypophosphatemia is the Expected Electrolyte Abnormality
In a cachectic patient with obstructing esophageal cancer and >20% weight loss starting preoperative TPN, hypophosphatemia is the most expected electrolyte abnormality due to refeeding syndrome. 1
Understanding the Clinical Context
This patient presents with multiple high-risk features for refeeding syndrome 1:
- Severe malnutrition with >20% weight loss over 3 months creates metabolic adaptation with depleted intracellular electrolytes 1
- Esophageal obstruction has caused prolonged inadequate nutrient intake, worsening the catabolic state 1
- Cancer cachexia involves cytokine-induced metabolic alterations that prevent normal nutrient utilization 2
Why Hypophosphatemia Occurs
When TPN is initiated in severely malnourished patients, the sudden glucose load triggers insulin release, which drives phosphate (along with potassium and magnesium) intracellularly for glucose metabolism 1. The body's phosphate stores are already depleted from prolonged starvation, making this intracellular shift particularly dangerous 1.
Hypophosphatemia is the most characteristic and clinically significant electrolyte abnormality in refeeding syndrome, according to the American Society for Parenteral and Enteral Nutrition 1.
Clinical Significance
Severe hypophosphatemia can cause 1:
- Respiratory muscle weakness - potentially complicating post-surgical recovery
- Cardiac dysfunction - including arrhythmias and heart failure
- Neurological complications
- Hemolytic anemia
Why Not the Other Options?
- Hypokalemia is the second most common abnormality in refeeding syndrome but less characteristic than hypophosphatemia 1
- Hypocalcemia is not a primary feature of refeeding syndrome
- Hypernatremia is not associated with refeeding syndrome; in fact, cancer patients with intestinal obstruction often have expansion of extracellular water volume 2
- Hyperphosphatemia is the opposite of what occurs in refeeding syndrome
Prevention Strategy
To prevent refeeding syndrome in this high-risk patient 1, 3:
- Start TPN at 25% of calculated energy requirements (approximately 20-25 kcal/kg/day) 1
- Prophylactically supplement phosphate before and during initial TPN administration 1
- Monitor serum phosphate, potassium, and magnesium daily for the first week 1
- Gradually increase caloric load over approximately 3 days 3
- Administer vitamin B1 prior to starting glucose infusion to reduce risk of Wernicke's encephalopathy 3
Common Pitfall
The most critical error is starting TPN at full caloric requirements in severely malnourished patients, which precipitates severe hypophosphatemia and potentially fatal complications 1. Always start low and advance slowly in patients with significant weight loss.