What is the cause of the electrolyte imbalance in an ICU patient with a high output fistula on Total Parenteral Nutrition (TPN) who became comatose after TPN was stopped to administer 2 units of Packed Red Blood Cells (PRBCs) through the same line?

Hypoglycemia is the Cause of Electrolyte Imbalance in ICU Patient with High Output Fistula

The most likely cause of the comatose state in this ICU patient with high output fistula is hypoglycemia (option A), resulting from the abrupt discontinuation of TPN while administering blood products through the same line.

Pathophysiology of the Case

• The patient was receiving TPN for nutritional support due to high output fistula, which is a common management approach for patients with gastrointestinal fistulas to maintain fluid, electrolyte, and nutritional balance 1
• TPN was discontinued to administer 2 units of PRBCs through the same line
• After 2 hours, the patient became comatose, indicating an acute metabolic derangement

Why Hypoglycemia is the Most Likely Cause

• Abrupt discontinuation of TPN in a patient dependent on it for glucose supply leads to rapid hypoglycemia, especially in critically ill patients 2
• High output fistulas cause significant fluid and electrolyte losses, making patients more vulnerable to metabolic derangements 3
• The timeline of symptom onset (2 hours after TPN discontinuation) is consistent with hypoglycemia development after cessation of continuous glucose infusion 2
• Coma is a classic manifestation of severe hypoglycemia in hospitalized patients 4

Why Other Electrolyte Disturbances Are Less Likely

Hypocalcemia (Option B)

• While hypocalcemia can occur in patients with high output fistulas and those on TPN, it typically develops more gradually and would not manifest so quickly after TPN discontinuation 2
• Severe hypocalcemia typically presents with neuromuscular irritability, tetany, and seizures rather than immediate coma 2

Hypokalemia (Option C)

• Hypokalemia is common in patients with high output fistulas and those on TPN therapy 2
• However, hypokalemia typically causes muscle weakness, cardiac arrhythmias, and paralysis before progressing to altered mental status 5
• The rapid onset of coma is not characteristic of isolated hypokalemia 5

Hyponatremia (Option D)

• Hyponatremia develops gradually and would not manifest so quickly after TPN discontinuation 5
• While severe hyponatremia can cause altered mental status and coma, it typically develops over a longer period 5

Clinical Implications and Management

• Immediate blood glucose measurement is essential in any patient who becomes comatose after TPN discontinuation 2
• Treatment involves prompt administration of intravenous glucose (D50W) followed by continuous glucose infusion until TPN can be safely restarted 2
• Prevention strategies include:
  • Never abruptly discontinue TPN in dependent patients 2
  • If TPN must be interrupted, provide alternative glucose sources or taper the rate gradually 2
  • Use separate dedicated lines for blood product administration in TPN-dependent patients 2

Monitoring Recommendations

• Electrolyte abnormalities are common in ICU patients, especially those with high output fistulas, and should be closely monitored 2
• Regular monitoring of serum glucose levels is essential when TPN is interrupted for any reason 2
• Patients with high output fistulas require vigilant monitoring of all electrolytes, particularly potassium, phosphate, and magnesium 2

This case highlights the critical importance of maintaining glucose homeostasis in TPN-dependent patients and the need for protocols to safely manage TPN interruptions when administering blood products.