A 34-year-old male is brought to the emergency room after being involved in a motor vehicle accident. He suffers blunt abdominal trauma and bilateral femur fractures. He has no significant past medical history. On physical examination, his blood pressure is 80/40 mmHg and his heart rate is 110/min. He receives several units of packed red blood cells. Once stabilized, the patient begins complaining of a tingling sensation in his toes and fingers. His serum calcium level is noted to be 7.2 mg/dL. Which of the following is the most likely cause of this patient's current symptoms?
This patient is experiencing paresthesias due to hypocalcemia. Evidently, he has had significant blood loss as a result of his injuries, and has received packed red blood cells as part of the resuscitation efforts. Prior to storage, whole blood (for transfusions) is generally mixed with solutions containing citrate anticoagulant. Packed cells derived from these whole blood collections also contain citrate. Infused citrate can chelate serum calcium, causing hypocalcemia. (This is most likely after massive transfusions of the equivalent of more than one blood volume over 24 hours.)
(Choice C) Stored red blood cells gradually lose intracellular potassium to the surrounding solution. This mechanism has the potential to cause hyperkalemia, but not hypocalcemia.
Educational Objective:
Patients who have received the equivalent of more than one blood volume of blood transfusions or packed red blood cells over 24 hours may develop elevated plasma levels of citrate (a substance added to stored blood). Citrate chelates calcium and magnesium and may reduce their plasma levels, causing paresthesias.