Effects of Magnesium Sulfate in a Newborn Piglet Meconium Aspiration Model

Abstract

OBJECTIVE: To examine the hemodynamic effects of magnesium sulfate (MgSO₄) in a neonatal model of meconium aspiration syndrome. DESIGN: A prospective animal study. PATIENTS AND PARTICIPANTS:Eight anesthetized neonatal piglets. METHODS: Animals were instrumented under fentanyl anesthesia for the determination of pulmonary and systemic blood pressures and cardiac index. A model of meconium aspiration was produced by instilling 6 to 7 ml of 20% fresh human meconium in normal saline down the endotracheal tube, resulting in hypoxemia (mean arterial O₂ saturation 73 SD, 10%), respiratory acidosis (mean pH 7.08, SD 0.04; PACO₂ 89, SD 2 torr), and pulmonary arterial hypertension (mean pulmonary artery pressure 52 SD, 5 mm Hg). A total of four aliquots of MgSO₄ (25 mg/kg equivalent to 0.1 mM/kg of magnesium) were administered intravenously to five animals (total of 100 mg/kg MgSO₄). Three animals served as controls and did not receive MgSO₄. RESULTS: Each dose of MgSO₄ was associated with a transient decrease in heart rate, cardiac index, pulmonary and systemic arterial pressures, and SAO₂, followed by a partial gradual recovery of all these variables within 2 to 3 minutes. According to measurements taken after MgSO₄ therapy, there was a significant decrease in arterial saturations (from 73 SD (10%) to 63 SD (13%); p < 0.05), mean systemic blood pressure (from 77 SD (16 mm Hg) to 74 SD (15 mm Hg); p < 0.05) and pulmonary artery pressure (to 52 SD (5 mm Hg); p < 0.05). The ratio between pulmonary and systemic vascular resistance was not significantly affected by MgSO₄ therapy. There were no changes in the control animals. CONCLUSION: The administration of magnesium sulfate is associated with increased hypoxemia in this model of meconium aspiration syndrome, probably because of worsening ventilation perfusion mismatch. These data do not provide any physiological support for the use of MgSO₄ in the neonate with meconium aspiration and pulmonary hypertension and suggest that this agent should be used cautiously, if at all, in such situations.