The relationship between plasma ionized concentration of calcium and magnesium with cardiac energetics and systemic oxygen transport in neonates after the Norwood procedure

  • Dr Hargen Zhang, Heart Center, Hospital for Sick Children, Canada
  • Dr Helen Holtby, Heart Center, Hospital for Sick Children, Toronto, Canada
  • Sally Cai, Data Center, Congenial Heart Surgeon's Society, Canada
  • Dr Jia Li, Department of Cardiology, Stollery Children's Hospital, Canada

    • Objective: We examined the relationship between Ca2+ and Mg2+ and systemic oxygen transport in neonates after the Norwood procedure.

    Methods: Oxygen consumption (VO2) was measured using respiratory mass spectrometry for 72 hrs in 17 neonates. Arterial, superior vena cava and pulmonary venous gases and pressures with Ca2+ and lactate were measured 2-4 hourly to calculate cardiac output (CO), systemic vascular resistance (SVR), rate pressure product (RPP), cardiac power output (CPO), systemic oxygen delivery (DO2) and oxygen extraction ratio (ERO2). Mg2+ was measured 4-12 hourly.

    Results: Ca2+ decreased in 8 hrs from 1.08±0.13 to 0.98±0.08 mmol/L, followed by an increase to 1.10±0.26 mmol/L at 72 hrs (p<0.0001). Mg2+ decreased in 24 hrs from 1.57±0.29 to 0.94±0.14 mmol/L, followed by a slow decrease to 0.67±0.16 mmol/L (p<0.0001). Mg2+ positively correlated with CO (p=0.008) and CPO (p=0.01), and negatively with heart rate (p=0.05). It trended to positively correlate with DO2 (p=0.08), and negatively with VO2 (p=0.08), ERO2 (p=0.04) and lactate (p=0.05). Negative trends were found between Mg2+ and SAP (p=0.16), RPP (p=0.14) and SVR (p=0.64). Ca2+ showed opposite trends without achieving significance in these variables except lactate (p=0.007). For a given CPO, Mg2+ negatively correlated with RPP (p=0.01), and Ca2+ showed a positive trend (p=0.50).
    Conclusion: Mg2+ exerts favorable effects on myocardial energetics and systemic oxygen transport in neonates after the Norwood procedure, whereas Ca2+ might be harmful. Maintaining a relatively high Mg2+ and low Ca2+ may promote the efficiency of myocardial work and improve oxygen transport in neonates after CPB.