Evaluating the delivery of nebulized and metered-dose inhalers in an in vitro infant ventilator lung model

In vitro evaluation of bronchodilator drug delivery by jet nebulization during pediatric mechanical ventilation

OBJECTIVE

To determine the influence of jet nebulizer brands and nebulization mode on albuterol delivery in a mechanically ventilated pediatric lung model.

DESIGN

In vitro, laboratory study.

SETTING

Research laboratory of a university hospital.

INTERVENTIONS

Using albuterol as a marker, six jet nebulizers (Microneb NA420, Sidestream, Acorn II, Cirrus, Upmist, Micro Mist) were tested in four nebulization modes in a bench model mimicking the ventilatory pattern of a 10-kg infant (Galileo ventilator, Hamilton Medical). The amounts of albuterol deposited on the inspiratory filters at the end of the endotracheal tube were determined, as well as the pressure, flow profiles, and particle size distribution of the jet nebulizers.

MEASUREMENTS AND MAIN RESULTS

Pooling the data of the six jet nebulizer brands (n = 30) indicated that intermittent nebulization during the expiratory phase was more efficient (6.5 +/- 2.5% of the initial dose, p < .001) than intermittent nebulization during the inspiratory phase (1.9 +/- 1.2%) and continuous nebulization with air from the ventilator (4.0 +/- 1.5%) or from an external source (4.2 +/- 1.4%). The particle size distribution at 6 L x min(-1) was between 2.81 and 3.30 microm.

CONCLUSIONS

In our in vitro pediatric lung model, the quantity of inhaled drug was low. Jet nebulizer brands and nebulization modes significantly affected drug delivery, and in vitro models designed for adults cannot be extrapolated to infants.

Neonatal Chronic Lung Disease

Chronic lung disease (CLD), formerly known as bronchopulmonary dysplasia, is presently defined as the need for oxygen therapy either at 28 days of age or greater than 36 weeks postmenstrual age. Clinical signs and symptoms include tachypnea, retractions, apnea, and radiographic findings of poorly inflated lungs with reticulogranular opacities. The disease develops as a result of chronic pulmonary inflammation and continuous lung injury induced by oxygen, positive pressure ventilation, and other causes. Fifty to sixty-five percent of neonates with CLD are rehospitalized with respiratory problems, and 21% of very low birth weight neonates are diagnosed with asthma or other respiratory disorders by the age of five. These infants are at risk of adverse neurodevelopmental sequelae as they have a more complicated neonatal course. Many studies have explored various preventive therapies including α1-proteinase inhibitors, superoxide dismutase, antioxidants, and ventilatory management. Although the results from these trials are promising, further studies are needed to define which patients are most likely to benefit from preventive therapy. Two preventive treatment approaches that have shown a decrease in morbidity and an improvement in mortality are antenatal steroids and surfactant therapy. Postnatal corticosteroid therapy continues to be the mainstay of treatment for CLD, however, there are a number of detrimental side effects associated with this treatment. Due to the increased incidence in periventricular leukomalacia, early treatment of steroid therapy cannot be recommended. The optimal time to start steroid therapy appears to be after the first week of life. In addition, the lowest dose and shortest duration of treatment needs to be implemented in order to minimize potential complications. Although bronchodilators and diuretics continue to be used extensively in infants with CLD, there are surprisingly few well-controlled studies that have evaluated the clinical impact of this therapy. Further trials are needed in order to support the routine use of these therapies in CLD. Unfortunately, inhaled steroids have not shown an improvement in long-term outcomes of CLD, however, they have shown a decrease in systemic steroid usage. CLD is a complex disease with many unanswered questions. Further studies are needed to evaluate the effects of various treatment modalities with particular focus on the long-term outcomes such as oxygen and ventilator dependency as well as the incidence of CLD.