METHYLPREDNISOLONE ATTENUATES THE PULMONARY HYPERTENSIVE RESPONSE IN PORCINE MECONIUM ASPIRATION

Severe neonatal aspiration of meconium is frequently complicated by fa tal pulmonary hypertension. The protective effect of an i.v. bolus of methylprednisolone on meconium aspiration-induced hypertensive lung in jury was studied in anesthetized pigs with adapted lung circulation. E leven 10-wk-old pigs received 3 mL/kg 20% human meconium via the endot racheal tube. Five of them were pretreated with 30 mg/kg methylprednis olone 30 min before aspiration. Ventilator settings were adjusted to k eep arterial PO2 above 8 kPa and arterial PCO2 below 5 kPa. Meconium i nsufflation induced a biphasic pulmonary presser response during the 6 h follow-up. Methylprednisolone tended to prevent the early (0-1 h) i ncrease in pulmonary artery pressure and inhibited significantly the s econd phase (1-6 h) progressive rise in pulmonary artery pressure and pulmonary vascular resistance. This inhibition of resistance increase was most profound in the postarterial segment of the lung circulation, as determined by pulmonary artery occlusion. Additionally, the methyl prednisolone pretreated group demonstrated a significant decrease in v enous admixture together with improved oxygenation during the late pha se after the insult, and further showed evidence of diminished lung ed ema formation. Although meconium aspiration-induced fall in blood leuk ocyte concentration was inhibited by methylprednisolone pretreatment, no histologic difference was found in pulmonary leukocyte sequestratio n. Our results thus show that in adapted porcine lungs methylprednisol one pretreatment improves oxygenation and attenuates the meconium aspi ration-induced pulmonary hypertensive response by preventing the incre ase in the postarterial resistance.