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Aerosol delivery in neonatal ventilator circuits: A rabbit lung model

The benefits of inhaled therapy in ventilated neonates are recognized, but the reliability of drug delivery in nebulizer‐ventilator circuits is uncertain. We quantified the effect of changing variables. Twenty‐three freshly killed rabbits (1.15–1.9 kg) were ventilated via a tracheostomy by a pressure‐limited, time‐cycled ventilator (Neovent). A radioaerosol of 99Tcm pertechnetate from an Ultravent nebulizer (Mallinkrodt) was fed into the proximal ventilator tubing. Two 3‐minute nebulizations at “standard settings” were followed by 2 at altered pressure, frequency, gas flow, I:E ratio, or position of the nebulizer in the circuit. Each nebulization was followed by a 3‐minute gamma camera image and total deposited radioactivity was measured in excised lungs and trachea. Images demonstrated good peripheral aerosol deposition. At standard settings, lung deposition averaged 2.8% of the aerosol released. This was decreased markedly by reducing tidal volume (ventilator pressures) and residence time of aerosol (I:E ratio). Reduced gas flow decreased deposition slightly, presumably by increased particle size and marginally reduced tidal volume. Deposition did not change with increased frequency; increased minute ventilation was offset by decreased residence time of the aerosol. We conclude that the Ultravent nebulizer can be used to nebulize drugs in a standard neonatal circuit, although the dose delivered is small. Tidal volume and aerosol residence time are important determinants of aerosol delivery. Pediatr Pulmonol 1991; 10:208–213.