The concentration of calcium in neonatal cardioplegia

Abstract

The optimal calcium concentration in cardioplegia for the newborn has not been determined. Therefore, the effect of 0, 0.6, 1.2, 1.8, and 2.4 mmol/L calcium in modified St. Thomas cardioplegia was evaluated in isolated working hearts of 7- to 10-day-old rabbits. Functional recovery was determined by comparing aortic flow, developed pressure, and first derivative of left ventricular pressure ( dP / dt ) before and after 1 hour of normothermic (37 °C) ischemia. As percentages of baseline values, recovery of developed pressure and dP / dt averaged 10% ± 1% (mean ± standard error of the mean) and 10% ± 1% with 0 mmol/L, 46% ± 7% and 44% ± 8% with 0.6 mmol/L, 79% ± 2% and 76% ± 2% with 1.2 mmol/L, 67% ± 2% and 61% ± 5% with 1.8 mmol/L, and 65% ± 5% and 65% ± 7% with 2.4 mmol/L calcium, respectively. Significant improvement in recovery of developed pressure and dP / dt was detected when the calcium concentration was increased from 0 to 0.6 mmol/ L and from 0.6 to 1.2 mmol/L, but the groups with 1.2, 1.8, and 2.4 mmol/L did not differ from one another significantly in terms of developed pressure and dP / dt recovery. There was no recovery of aortic flow when 0 mmol/L calcium was used; at calcium concentrations of 0.6, 1.2, 1.8, and 2.4 mmol/L, recovery of aortic flow averaged 16% ± 7%, 63% ± 10%, 23% ± 10%, and 36% ± 11% of baseline values, respectively. Recovery of aortic flow with 1.2 mmol/L calcium was significantly higher than at concentrations of 0.6 and 1.8 mmol/L. In the rabbit exposed to normothermic ischemia, we conclude that neonatal cardioplegia requires calcium to be effective and that 1.2 mmol/L represents the optimal calcium concentration for the best combination of recovery in aortic flow and developed pressure.