AEROSOL DELIVERY FROM A METERED-DOSE INHALER DURING MECHANICAL VENTILATION - AN IN-VITRO MODEL

Successful bronchodilator therapy with a metered-dose inhaler (MDI) in intubated, mechanically ventilated patients requires adequate deliver y of aerosol to the lower respiratory tract. We determined the effect of ventilator mode, inspiratory flow pattern, humidity, and spontaneou s respiratory effort on albuterol delivery in a model of the trachea a nd bronchi. The model was ventilated through an endotracheal tube duri ng controlled mechanical ventilation (CMV), assist control (At), press ure support (PS), and continuous positive airway pressure (CPAP), sepa rately with a dry and humidified ventilator circuit. Delivery of albut erol administered by a MDI and spacer on filters placed at the ends of the bronchi was measured by spectrophotometry (246 nm). Under dry con ditions and with a frequency of 10 breaths/min, albuterol delivery wit h CMV (VT, 800 mi; 30.3 +/- 3.4%), At (VT, 800 mi; 31.9 +/- 1.3%), PS 10 cm H2O (VT, 700 mi; 28.8 +/- 4.5%), or PS 20 cm H2O (VT, 800 ml; 30 .9 +/- 1.8%) was lower than that observed with simulated spontaneous b reaths with CPAP (VT, 800 mi; 39.2 +/- 1.4%) (p < 0.01 for all modes). Delivery was greater under dry (28.8 to 39%) than under humidified co nditions (15.9 to 20.2%) (p < 0.005 in all modes). Albuterol delivery showed a linear correlation with both inspiratory time and duty cycle (r > 0.91). Lower respiratory tract delivery of aerosol from a MDI var ied from 4.9 to 39.2%. We conclude that in addition to other known fac tors such as dose, type of spacer, and its position the technique of a dministering MDIs in mechanically ventilated patients markedly influen ces lower respiratory tract aerosol delivery.