MECONIUM ASPIRATION INDUCES A CONCENTRATION-DEPENDENT PULMONARY HYPERTENSIVE RESPONSE IN NEWBORN PIGLETS

To investigate the effects of aspirating different meconium concentrat ions on the pulmonary circulation in 10- to 12-day-old piglets, 30 cat heterized animals were studied. The piglets received an intratracheal bolus oi 3 ml/kg of a mixture of human meconium in saline with concent rations of 20 mg/ml (light, n = 7), 40 mg/ml (moderate, n = 6), or 65 mg/ml (thick, n = 10) meconium in saline. Control piglets (n = 7) rece ived 3 ml/kg of intratracheal saline. Pulmonary and systemic pressures were measured and vascular resistances calculated at baseline and ser ially for 4 hours after instillation. Four of the piglets died early a nd were excluded from the study. In addition, 23 samples of human meco nium-stained amniotic fluid were collected at delivery for determinati on of their meconium concentration. After an initial rise in pulmonary artery pressure and vascular resistance after meconium and saline ins tillation, pulmonary artery pressure and resistance increased progress ively and concentration-dependently in the meconium groups, but return ed to baseline in the control group. The saline and meconium-induced i nitial increases, and the subsequent meconium-stimulated progressive r ise in vascular resistance occurred mainly in the postarterial segment . There were no significant changes in systemic hemodynamics. Mean air way pressure increased and oxygenation deteriorated after meconium ins tillation. The impairment of oxygenation depended on the meconium conc entration in the instilled bolus and persisted throughout the study af ter moderate and thick meconium instillation. Similarly, the intrapulm onary shunt fraction increased initially and remained elevated in the moderate and thick meconium groups. Meconium concentrations in the hum an amniotic fluid samples were in the same range as concentrations use d in the present experimental study. These results indicate that aspir ated meconium at concentrations found in light to moderate meconium-st ained human amniotic fluid has significant effects on pulmonary hemody namic and oxygenation in newborn piglets. (C) 1998 Wiley-Liss, Inc.