Effects of Conventional Mechanical Ventilation Performed by Two Neonatal Ventilators on the Lung Functions of Rabbits with Meconium-Induced Acute Lung Injury

Severe meconium aspiration syndrome (MAS) in the neonates often requires a ventilatory support. As a method of choice, a conventional mechanical ventilation with small tidal volumes (V_T<6 ml/kg) and appropriate ventilatory pressures is used. The purpose of this study was to assess the short-term effects of the small-volume CMV performed by two neonatal ventilators: Aura V (Chirana Stara Tura a.s., Slovakia) and SLE5000 (SLE Ltd., UK) on the lung functions of rabbits with experimentally-induced MAS and to estimate whether the newly developed neonatal version of the ventilator Aura V is suitable for ventilation of the animals with MAS.

In the young rabbits, a model of MAS was induced by an intratracheal instillation of a suspension of neonatal meconium (4 ml/kg, 25 mg/ml). After creating the model of MAS, the animals were ventilated with small-volume CMV (frequency 50/min, V_T <6 ml/kg, inspiration time 50 %, fraction of inspired oxygen 1.0, positive end-expiratory pressure 0.5 kPa, mean airway pressure 1.1 kPa) performed by ventilator Aura V (Aura group, n=7) or ventilator SLE5000 (SLE group, n=7) for additional 4 hours. One group of animals served as healthy non-ventilated controls (n=6). Blood gases, oxygenation indexes, ventilatory pressures, lung compliance, oxygen saturation and total and differential white blood cell (WBC) count were regularly determined. After euthanizing the animals, a left lung was saline-lavaged and total and differential counts of cells in the bronchoalveolar lavage (BAL) fluid were determined. A right lung was used for estimation of lung edema formation (expressed as a wet/dry weight ratio) and for analysis of concentrations of pro-inflammatory cytokines (IL-1β, IL-8, TNF). The cytokines were measured also in the blood plasma taken at the end of experiment.

Meconium instillation seriously worsened the gas exchange and induced inflammation and lung edema formation. In the Aura group, slightly lower concentrations of cytokines were found and better gas exchange early after creating the MAS model was observed. However, there were no significant differences in the respiratory parameters between the ventilated groups at the end of experiment (P>0.05).

Concluding, the newly developed neonatal version of the ventilator Aura V was found to be fully comparable to widely used neonatal ventilator SLE5000. Results provided by Aura V in CMV ventilation of rabbits with meconium-induced acute lung injury suggest its great potential also for future clinical use, i.e. for ventilation of the neonates with MAS.