CONTRIBUTION OF AIRWAY HYPERRESPONSIVENESS TO LOWER AIRWAY-OBSTRUCTION AFTER EXTRACORPOREAL MEMBRANE-OXYGENATION FOR MECONIUM ASPIRATION SYNDROME

Objective: To determine whether airway hyperresponsiveness contributes to the development of lower airway obstruction in infants recovering from severe meconium aspiration syndrome treated with extracorporeal m embrane oxygenation (ECMO). Design: Prospective comparison study of th e response to bronchodilator during the acute and convalescent phase o f severe meconium aspiration. Setting: Pediatric/neonatal intensive ca re unit in a tertiary care hospital. Patients: Seven neonates with sev ere meconium aspiration syndrome that was refractory to conventional m echanical ventilation, requiring ECMO treatment. Interventions: Evalua tion of the effect of bronchodilator treatment on the airway function at a postnatal age of 14 +/- 2.7 (SEM) days, after the patients had be en 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 a irway function were measured and compared before and after administrat ion of aerosolized isoetharine early in the course of ECMO and again s everal 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 wer e used for measuring respiratory system compliance and resistance. Mea surements and Main Results: During the first test, isoetharine produce d a mild increase in maximum expiratory flows at 25% (MEF(25)) of forc ed vital capacity (FVC) (48 +/- 27% compared with baseline values), wi thout significant change in the MEF(25) to FVC ratio. During the secon d test similar to 2 wks later (post-ECMO), isoetharine increased MEF(2 5) by 123 +/- 29% and increased the MEF(25)/FVC by 40 +/- 13% compared with baseline values. The percent change in both indices was signific antly higher during the second test (p <.05) than in the first test. C onclusions: Airway obstruction in infants recovering from severe mecon ium aspiration syndrome is partially reversible with aerosolized isoet harine, indicating that airway hyperresponsiveness contributes to the pathogenesis of airway obstruction.