Hypoglycemia is the Cause of Electrolyte Imbalance in the ICU Patient
The most likely cause of the electrolyte imbalance leading to coma in this ICU patient is hypoglycemia (option A) caused by stopping TPN while administering blood products through the same line.
Pathophysiology and Mechanism
When TPN was stopped and blood products were administered through the same line, the following sequence likely occurred:
Abrupt cessation of glucose supply: The patient was receiving TPN for a high-output fistula, which provided continuous glucose. When this was stopped, the patient's glucose supply was suddenly cut off 1.
Insulin effect: The patient likely had elevated insulin levels in response to the TPN. When the glucose supply was stopped but insulin remained active, severe hypoglycemia developed 2, 3.
Blood transfusion effect: Administering PRBCs through the same line that previously contained dextrose can create a situation where:
- Residual insulin in the bloodstream continues to act
- No replacement glucose is being provided
- The patient's metabolic state is already compromised due to the high-output fistula
Supporting Evidence
Patients with high-output fistulas have increased metabolic demands and are at risk for electrolyte disturbances 4.
The FDA label for dextrose warns that "the intravenous administration of this solution can cause fluid and/or solute overloading resulting in dilution of serum electrolyte concentrations" and that "significant hyperglycemia and possible hyperosmolar syndrome may result from too rapid administration" 1. The abrupt discontinuation can cause the opposite effect - severe hypoglycemia.
Studies have shown that during severe hypoglycemia, electrolyte disturbances are common, with hypokalemia being the most frequent (21.9% of cases) 3.
Massive insulin effect (in this case from continued insulin action after TPN cessation) can cause multiple electrolyte disorders including hypokalemia, hypophosphatemia, and hypomagnesemia 2.
Why Not the Other Options?
Hypocalcemia (B): While hypocalcemia can occur in patients on TPN, especially with refeeding syndrome 4, it typically doesn't develop so rapidly (within 2 hours) to cause coma unless extremely severe.
Hypokalemia (C): Although hypokalemia commonly occurs during severe hypoglycemia 3, it typically doesn't cause coma unless extremely severe.
Hyponatremia (D): Acute severe hyponatremia can cause coma, but it typically develops more gradually and is less likely to be the primary cause in this scenario 5.
Clinical Implications and Management
Immediate intervention:
- Administer IV dextrose (D50W) immediately
- Check blood glucose level stat
- Monitor electrolytes, particularly potassium, phosphate, and magnesium
Subsequent management:
- Restart TPN at appropriate rate after stabilization
- Monitor for rebound hyperglycemia
- Replace electrolytes as needed based on laboratory values
Prevention strategies:
- Never stop TPN abruptly without providing alternative glucose source
- When administering blood products, use a separate line or follow proper protocols for line flushing
- Monitor glucose levels closely when interrupting TPN for any reason
Pitfalls and Caveats
The ESPEN guidelines emphasize that "electrolytes abnormalities are common in patients with AKI, AKI on CKD, or CKD with KF receiving KRT and shall be closely monitored" 4. This applies to all critically ill patients, especially those with metabolic instability.
Refeeding syndrome can cause similar electrolyte abnormalities but typically develops over days rather than hours 4.
Blood products should not be administered through the same line as dextrose solutions without proper flushing due to the risk of pseudoagglutination 1.
Patients with high-output fistulas require meticulous attention to fluid and electrolyte balance 4.