Influence of inspiratory flow pattern and nebulizer position on aerosol delivery with a vibrating-mesh nebulizer during invasive mechanical ventilation: an in vitro analysis.

Abstract

Aerosol delivery during invasive mechanical ventilation (IMV) depends on nebulizer type, placement of the nebulizer and ventilator settings. The purpose of this study was to determine the influence of two inspiratory flow patterns on amikacin delivery with a vibrating-mesh nebulizer placed at different positions on an adult lung model of IMV equipped with a proximal flow sensor (PFS). IMV was simulated using a ventilator connected to a lung model through an 8-mm inner-diameter endotracheal tube. The impact of a decelerating and a constant flow pattern on aerosol delivery was evaluated in volume-controlled mode (tidal volume 500 mL, 20 breaths/min, inspiratory time of 1 sec, bias flow of 10 L/min). An amikacin solution (250 mg/3 mL) was nebulized with Aeroneb Solo(®) placed at five positions on the ventilator circuit equipped with a PFS: connected to the endotracheal tube (A), to the Y-piece (B), placed at 15 cm (C) and 45 cm upstream of the Y-piece (D), and placed at 15 cm of the inspiratory outlet of the ventilator (E). The four last positions were also tested without PFS. Deposited doses of amikacin were measured using the gravimetric residual method. Amikacin delivery was significantly reduced with a decelerating inspiratory flow pattern compared to a constant flow (p<0.05). With a constant inspiratory flow pattern, connecting the nebulizer to the endotracheal tube enabled similar deposited doses than these obtained when connecting the nebulizer close to the ventilator. The PFS reduced deposited doses only when the nebulizer was connected to the Y-piece with both flow patterns or placed at 15 cm of the Y-piece with a constant inspiratory flow (p<0.01). Using similar tidal volume and inspiratory time, a constant flow pattern (30 L/min) delivers a higher amount of amikacin through an endotracheal tube compared to a decelerating inspiratory flow pattern (peak inspiratory flow around 60 L/min). The optimal nebulizer position depends on the inspiratory flow pattern and the presence of a PFS.