Management of a Piglet Model of the Meconium Aspiration Syndrome With High-Frequency or Conventional Ventilation

OBJECTIVE: To assess the usefulness of three methods of high-frequency ventilation in the early management of a piglet model of the meconium aspiration syndrome. DESIGN: Randomized, block design. SETTING: Animal research facility. SUBJECTS: Fifty-six mixed-breed newborn piglets aged 1 to 4 days and weighing 1.8 to 2.7 kg. INTERVENTIONS: After instillation of a 2.2-mL/kg solution of 25% meconium, 56 piglets were randomized to receive treatment with (1) a conventional positive-pressure infant ventilator, (2) the Bunnell Life Pulse high-frequency jet ventilator, (3) the Bird model VDR high-frequency flow interruptor, or (4) the Infant Star high-frequency flow interruptor. We adjusted ventilator settings to maintain partial pressures of arterial oxygen (PaO2) of 80 to 120 cm H2O and partial pressures of arterial carbon dioxide (PaCO2) of 30 to 50 cm H2O during the 6 hours of ventilation. MEASUREMENTS AND MAIN RESULTS: We compared pulmonary histologic alterations and four physiologic parameters: (1) mean airway pressure, (2) PaCO2, (3) ratio of PaO2 to partial alveolar oxygen pressure (PAO2), and (4) oxygenation index ([(fraction of inspired oxygen)(mean airway pressure)(100)]/PaO2). The two measures of oxygenation were similar for all four devices except at 4 hours, when the PaO2/PAO2 ratio on positive-pressure ventilation was significantly higher than that on high-frequency jet ventilation (P = .008). The histologic changes on positive-pressure ventilation (atelectasis, inflammation, presence of meconium, and exudative debris) were significantly worse than those on high-frequency jet ventilation or flow interruption (P < .0001). CONCLUSIONS: The finding of less severe pathologic alterations with various types of high-frequency ventilators justifies further investigations into the management of the meconium aspiration syndrome with these devices.