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 receiving 2 units of Packed Red Blood Cells (PRBCs) through the same TPN line?

Cause of Electrolyte Imbalance in ICU Patient After Blood Transfusion

The cause of the electrolyte imbalance in this ICU patient is hypoglycemia, which developed after abruptly stopping TPN and administering PRBCs through the same line. 1

Mechanism of the Problem

The scenario presents a critical error in clinical practice that led to the patient's comatose state:

1. Improper administration technique:

   • The nurse administered PRBCs through the same line as TPN without proper flushing
   • This violates a clear contraindication in the FDA drug label which states: "Dextrose injection without electrolytes should not be administered simultaneously with blood through the same infusion set because of the possibility that pseudoagglutination of red cells may occur" 2

2. Abrupt discontinuation of TPN:

   • The Clinical Nutrition Society explicitly recommends that "TPN should not be stopped abruptly without providing an alternative glucose source to prevent severe hypoglycemia and electrolyte disturbances" 1
   • Patients with high-output fistulas have increased metabolic demands and are particularly vulnerable to rapid metabolic changes 1

Why Hypoglycemia is the Most Likely Cause

The patient's comatose state is most consistent with severe hypoglycemia for several reasons:

• The timing of symptom onset (2 hours after TPN discontinuation) matches the rapid development of hypoglycemia
• Patients on long-term TPN develop insulin resistance and high insulin secretion; when TPN is abruptly stopped, the persistent insulin effect causes rapid glucose utilization without replacement
• Altered mental status progressing to coma is a classic presentation of severe hypoglycemia
• Patients with high-output fistulas have increased metabolic demands, making them particularly vulnerable to glucose depletion 1

Why Other Options Are Less Likely

• Hypocalcemia (B): While possible in patients with high-output fistulas, it typically develops more gradually and would not cause such rapid deterioration 1
• Hypokalemia (C): Can occur during severe hypoglycemia 3, but is more likely a consequence rather than the primary cause of the patient's comatose state
• Hyponatremia (D): Develops more gradually and would be unlikely to cause such rapid deterioration in this clinical scenario 4

Prevention and Management

To prevent this complication:

• Never administer blood products through the same line as dextrose solutions without proper flushing 2
• When TPN must be interrupted, provide an alternative glucose source or taper the TPN gradually 1
• Use separate dedicated lines for blood product administration
• Monitor blood glucose levels closely when TPN is interrupted for any reason

For immediate management of this patient:

1. Check blood glucose level immediately
2. Administer IV dextrose (D50W) if hypoglycemia is confirmed
3. Resume appropriate nutritional support once the patient is stabilized
4. Monitor electrolytes, as secondary electrolyte disturbances may occur during severe hypoglycemia 3

Clinical Pitfalls to Avoid

• Never stop TPN abruptly in metabolically unstable patients without an alternative glucose source
• Always use separate lines for blood products and TPN
• Remember that patients with high-output fistulas have higher metabolic demands and are more vulnerable to rapid metabolic changes 1
• Be aware that severe hypoglycemia can cause secondary electrolyte abnormalities, particularly hypokalemia 3