Differential Diagnosis for Electrolyte Imbalance

The patient's condition, involving a high output fistula on Total Parenteral Nutrition (TPN) and the administration of 2 units of Packed Red Blood Cells (PRBCs) through the same line as TPN, followed by coma, suggests a critical electrolyte imbalance. The key to this scenario is understanding the effects of stopping TPN and administering blood products through the same line.

• Single Most Likely Diagnosis

  • Hypoglycemia: Stopping TPN abruptly can lead to hypoglycemia, especially in patients who are entirely dependent on TPN for their glucose needs. The brain is highly dependent on glucose for energy, and hypoglycemia can rapidly lead to neurological deterioration, including coma.

• Other Likely Diagnoses

  • Hypocalcemia: Citrate, a preservative in blood products, can bind to calcium, potentially leading to hypocalcemia, especially with rapid or large-volume transfusions. Hypocalcemia can cause neurological symptoms, including confusion and, in severe cases, coma.
  • Hypokalemia: Although less directly related to the immediate scenario of stopping TPN and giving PRBCs, hypokalemia can occur due to the dilutional effect of transfused blood products or as a complication of the underlying condition requiring TPN. However, it's less likely to cause acute coma compared to hypoglycemia or hypocalcemia.

• Do Not Miss Diagnoses

  • Hyperkalemia: Although not an option provided, it's crucial to consider hyperkalemia as a potential complication of transfusing blood products, especially if the blood is old or if there's significant hemolysis. Hyperkalemia can lead to cardiac arrest and is a critical diagnosis not to miss.
  • Hyponatremia: While less directly related to the immediate effects of TPN cessation and PRBC transfusion, hyponatremia can occur due to the free water content in some blood products or as a complication of the patient's underlying condition. Severe hyponatremia can cause neurological symptoms, including coma.

• Rare Diagnoses

  • Other electrolyte imbalances: While the provided options focus on single electrolyte imbalances, it's essential to consider that critically ill patients, especially those on TPN, can have complex and multifactorial electrolyte disturbances. Other imbalances, such as hypomagnesemia, can also contribute to neurological symptoms but are less directly implicated in this specific scenario.