DELIVERY OF METERED-DOSE INHALER AEROSOLS TO PARALYZED AND NONPARALYZED RABBITS

Objective: To assess whether paralysis alters pulmonary deposition of albuterol delivered by metered dose inhaler and spacer to small animal s, Design: A parallel group study of intubated and ventilated rabbits, Interventions: Animals in group 1 (n = 7) were paralyzed with intrave nous pancuronium, and ventilated at a rate of 30 breaths/min, The anim als in group 2 (n = 6) were ventilated at a rate of 10 breaths/min und er light anesthesia without paralysis. In this latter group, spontaneo us respiration continued at a rate of 40 to 50 breaths/min, Both group s were maintained at PaCO2 of 35 to 40 torr (4.7 to 5.3 kPa), and othe r ventilatory settings were identical, Measurements and Main Results: Technetium-99m labeled albuterol aerosol was delivered by metered dose inhaler via a spacer device to both groups, Pulmonary deposition of t he aerosol, determined by measuring the radioactivity in the lung tiss ues at autopsy, was expressed as percent of the total radioactivity di spensed by the metered dose inhaler, Group 2 showed significantly grea ter lung deposition than group 1 (0.510 +/- 0.076 [SEM] % vs. 0.226 +/ - 0,054%, P = .0094), Deposition in the airway, the endotracheal tube, and the ventilator circuit did not differ significantly, Conclusion: Metered dose inhaler delivery of aerosolized medications to ventilated rabbits is significantly enhanced if respiration is not controlled, T his observation might have implications for the delivery of therapeuti c aerosols to newborns and young infants receiving slow, intermittent, mandatory ventilation.