1996 OPEN FORUM Abstracts
EXHALED AEROSOL ACCOUNTS FOR DISCREPANCIES IN MODELING OF DRUG DELIVERY DURING MECHANICAL VENTILATION.
I. Fink, R. Dhand, D. Naven, P. Fahey, M.J. Tobin. Hines VA Hospital and Loyola Univ Chicago, Hines IL
Differences in aerosol delivered in-vitro and deposited in the lower respiratory tract in-vivo may be due to the amount of aerosol filtered in models that are normally exhaled by patients. To determine the amount of aerosol exhaled by ventilated patients, we administered albuterol by metered dose inhaler (MDI) with spacer chamber into the inspiratory limb of a wet (35ºC, >99% RH) ventilator circuit during control mode (CMV). Albuterol deposition (246nm) was determined at the expiratory limb of the ventilator circuit. An in-vitro model was used to identify drug passing directly from the inspiratory to expiratory limb of the ventilator circuit under similar conditions. Drug exhaled in-vivo (8.7 %) was greater than that measured in-vitro (3.9%) (p < 0.001).
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4.8% of the nominal dose of the MDI is exhaled by the patient. Subtracting drug exhaled (4%) from previously reported in-vitro delivery (16%) results in correlation with adjusted deposition reported in-vivo (11-12%). In conclusion, adjusting in-vitro measurements for exhaled aerosol improves the correlation of in-vitro delivery with in-vivo deposition during mechanical ventilation.