Variations in total and ionized calcium during cardiac surgery

Area of Science:

• Cardiovascular Surgery
• Anesthesiology
• Clinical Chemistry

Background:

• Cardiopulmonary bypass (CPB) is a critical procedure in cardiac surgery.
• Maintaining electrolyte balance, particularly calcium levels, is essential during CPB.
• Variations in serum calcium can impact patient outcomes.

Purpose of the Study:

• To investigate changes in total and ionized serum calcium and urine calcium during CPB.
• To determine the effects of hemodilution, pharmacologic agents, and blood transfusions on calcium levels.
• To evaluate the efficacy of calcium chloride administration during CPB.

Main Methods:

• Studied 20 patients undergoing cardiac surgery.
• Analyzed serial blood and urine samples using a calcium electrode during CPB.
• Measured total and ionized serum calcium and urine calcium levels.
• Administered calcium chloride during the procedure.

Main Results:

• Total serum calcium decreased significantly after anesthesia induction (p < 0.05).
• Ionized calcium decreased after heparinization (p < 0.05) but was unaffected by protamine.
• The ratio of ionized to total calcium declined during CPB, returning to normal post-perfusion.
• Urinary calcium excretion did not correlate with hypocalcemia during bypass.
• Exogenous calcium chloride administration significantly increased post-perfusion ionized serum calcium (p < 0.05).

Conclusions:

• CPB, hemodilution, and citrated blood products contribute to decreased serum calcium levels.
• Anesthesia induction alone significantly reduces total serum calcium.
• Ionized calcium levels are affected by heparinization but not protamine.
• Urinary calcium excretion is not a primary cause of hypocalcemia during bypass.
• Calcium chloride administration effectively increases ionized calcium, but current protocols may be insufficient, necessitating adjustments.