Nebulized drug delivery in patients breathing spontaneously through an artificial airway.

During the past 25 years, incremental gains in knowledge about aerosol delivery to mechanically ventilated patients had a major impact on patient care in this setting. The complex array of factors influencing aerosol delivery during mechanical ventilation made it difficult to elucidate the contribution of individual parameters to optimal aerosol delivery. Over the ensuing years, bench models made invaluable contributions in elucidating the effects of each variable on the efficiency of aerosol delivery and in determining methods to maximize drug deposition in the lung, despite the poor efficiency of aerosol-generating devices, the presence of a ventilator circuit and artificial airway, differing ventilator modes and ventilatory parameters, and in many clinical situations, the occurrence of severe lung disease in the patient.1 The artificial airway was long believed to be a serious obstacle to effective aerosol delivery during mechanical ventilation. Impaction of aerosol on the endotracheal tube reduced the efficiency of lower airway delivery of drug, particularly in pediatric ventilator circuits (internal diameter of the artificial airway between 3 mm and 6 mm).2,3 However, nebulizer efficiency was not reduced with endotracheal tubes of internal diameter 7 mm.4 Earlier investigators may have overemphasized the impediments created by the artificial airway to aerosol delivery, probably because the aerosol generator was placed too close to the artificial airway. When the aerosol generator was placed at a distance from the endotracheal tube, instead of being directly connected to it, drug losses in the endotracheal tube were minimized and pulmonary deposition of aerosol was increased.4 Overall, in mechanically ventilated adults, the type of aerosol generator and the ventilatory parameters seemed to have a greater influence on aerosol deposition within the endotracheal tube than the diameter of the endotracheal tube per se.4 Critically ill patients in the ICU often require placement of an artificial airway to provide mechanical ventilation. In some situations (eg, during recovery from anesthesia or during weaning trials), patients may have an endotracheal tube while they are breathing spontaneously. Spontaneously breathing patients may also have tracheostomy tubes for extended periods while they are being weaned from the ventilator. Moreover, spontaneously breathing patients with chronic respiratory failure may require a tracheostomy tube, but no or periodic ventilator support, for a prolonged duration. Many such patients require aerosolized therapies, particularly inhaled bronchodilators, for relief of air-flow obstruction. In spontaneously breathing patients the efficiency of aerosol delivery is influenced by the drug output from the nebulizer, aerosol particle size, interface between the nebulizer and patient, and breathing pattern.5 Addition of an artificial airway in a spontaneously breathing patient adds another variable influencing aerosol deposition to the mix. Optimal methods for delivering aerosols in the setting of patients needing an artificial airway without ventilator support have not been well studied.