November 2002 / Volume 47 / Number 11 / Page 1279
Aerosol Delivery Through an Artificial Airway
IntroductionFor both lung and systemic diseases, aerosol delivery of drugs into the lungs can often offer substantial advantages over other routes of administration. In the intensive care unit, however, the artificial airway can be a substantial barrier to aerosol delivery, so clinicians must pay careful attention to the ventilator pattern, the delivery gas humidity/density, the device characteristics, and the circuit/tube properties. When those are optimized, aerosol delivery from a nebulizer or metered-dose inhaler and through an endotracheal tube can begin to approach that seen in a nonintubated patient. Novel approaches, such as generating the aerosol within the airway, offer the opportunity to greatly increase deposition efficiency and focal drug targeting in intubated patients.
Natural Versus Artificial Airways
Assessment of Aerosol Delivery Through Artificial Airways
In Vitro Measurements
In Vivo Assessments
Comparison of Aerosol Delivery With and Without an Artificial Airway
Factors Important in Optimizing Delivery Through an Artificial Airway
Ventilation Pattern and Timing
Carrier Gas Properties
Intra-Airway Delivery Systems
MDI Nozzle Extender
Intra-Airway Aerosol-Generating Catheter
Medication delivery into the airways of intubated patients can offer substantial advantages over parenteral or oral administration routes. For medications targeted at lung diseases, a higher therapeutic index can be achieved with drugs delivered directly to the site of intended action, with little or no systemic exposure. The lung can also be a useful portal for medications designed for systemic targets, because drugs that can easily pass through the alveolar-capillary interface (eg, insulin) can be exposed to a large lung surface area in contact with the entire cardiac output.
Effective aerosolized medication delivery into the lungs of intubated patients depends on many of the same factors important in nonintubated patients: efficient device output, small particle size, low-velocity gas flow, large inspired volume, and breath-hold at end inspiration. The intubated patient, however, offers additional challenges: the artificial airway is a different geometry than the natural airway; the aerosol delivery system is generally attached to the ventilator circuit in which heat, humidification, and bias gas flows may be present; pressure gradients down the airways are different than during spontaneous breathing; and the required mechanical ventilatory pattern may not be ideal for aerosol delivery. In this paper I review these issues and examine some novel design concepts that may help optimize aerosol delivery.