ObjectiveTo determine whether airway hyperresponsiveness contributes to the development of lower airway obstruction in infants recovering from severe meconium aspiration syndrome treated with extracorporeal membrane oxygenation (ECMO).DesignProspective comparison study of the response to bronchodilator during the acute and convalescent phase of severe meconium aspiration.SettingPediatric/neonatal intensive care unit in a tertiary care hospital.PatientsSeven neonates with severe meconium aspiration syndrome that was refractory to conventional mechanical ventilation, requiring ECMO treatment.InterventionsEvaluation of the effect of bronchodilator treatment on the airway function at a postnatal age of 14 +/- 2.7 (SEM) days, after the patients had been off ECMO for 4.6 +/- 1.4 days, and comparison with the response the same patients had shown at a postnatal age of 2.7 +/- 0.6 days, when they had been on ECMO for 1.3 +/- 0.6 days. Lung mechanics and lower airway function were measured and compared before and after administration of aerosolized isoetharine early in the course of ECMO and again several days after ECMO. Maximum expiratory flow-volume curves produced by the deflation flow-volume curve technique were used for evaluating the lower airway function, and partial passive flow-volume curves were used for measuring respiratory system compliance and resistance.Measurements and Main ResultsDuring the first test, isoetharine produced a mild increase in maximum expiratory flows at 25% (MEF25) of forced vital capacity (FVC) (48 +/- 27% compared with baseline values), without significant change in the MEF25to FVC ratio. During the second test approximate 2 wks later (post-ECMO), isoetharine increased MEF25by 123 +/- 29% and increased the MEF25/FVC by 40 +/- 13% compared with baseline values. The percent change in both indices was significantly higher during the second test (p < .05) than in the first test.ConclusionsAirway obstruction in infants recovering from severe meconium aspiration syndrome is partially reversible with aerosolized isoetharine, indicating that airway hyperresponsiveness contributes to the pathogenesis of airway obstruction.(Crit Care Med 1995; 23:749-754)