Management of a piglet model of the meconium aspiration syndrome with high-frequency or conventional ventilation
T. E. Wiswell, N. H. Foster, M. V. Slayter and W. E. Hachey
Department of Pediatrics, Walter Reed Army Medical Center, Washington, DC 20307-5001.
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.
