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In vitro evaluation of aerosol bronchodilator delivery during mechanical ventilation: pressure-control vs. volume
Dean R Hess1, Christine Dillman, Robert M Kacmarek
1Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA. dhess@partners.org
Objective:
To determine the effect of inspiratory time and inspiratory flow pattern on albuterol delivery by aerosol during mechanical ventilation.
Design:
A ventilator was connected to a lung model and set to deliver a tidal volume of 0.6 l, PEEP 5 cmH(2)O, and respiratory rate of 15/min. We evaluated inspiratory times of 1 and 2 s, lung mechanics of 0.05 l/cmH(2)O compliance and 50 cmH(2)O/l/s resistance, or 0.02 l/cmH(2)O compliance and 5 cmH(2)O/l/s resistance, and three inspiratory flow patterns (constant flow volume-controlled ventilation, descending ramp flow volume-controlled ventilation, and pressure-controlled ventilation). Albuterol was delivered into the ventilator circuit by a nebulizer containing 5 mg (4 ml) albuterol or a pMDI and spacer (four actuations; 360 micro g). A filter between the Y-piece and the lung model collected the aerosol, which was analyzed for albuterol by spectrophotometry.
Results:
For the nebulizer there were significant differences in albuterol delivered for inspiratory time, flow pattern, and lung mechanics. For the pMDI there were no significant differences for the amount of albuterol delivered for inspiratory time, flow pattern, or lung mechanics.
Conclusions:
Albuterol delivery by nebulizer is affected by inspiratory time and inspiratory flow pattern. When a pMDI is used, the amount of albuterol delivered is not affected by inspiratory flow pattern or inspiratory time.