Bronchodilator delivery by pressurized metered-dose inhaler (pMDI) to patients on mechanical ventilation is best achieved without breaking the breathing circuit. We describe an evaluation of an improved CHC (AeroVent Plus*, Trudell Medical International, London, Canada (n=5 devices, 1 measurement/device)), in which the pMDI canister receptacle is offset from the CHC axis to reduce internal impaction, and can also accept GSK pMDI canisters having a dose counter. Delivery of 3-actuations of salbutamol (HFA-Ventolin*, GSK (Canada); 100-μg/actuation) was assessed with the expanded CHC inserted in the inspiratory limb of an adult breathing circuit equipped with a 7-mm diameter endotracheal tube (ETT). An adult test lung (Michigan Instruments) was used to simulate the patient. The circuit was humidified near to body conditions (T = 36°C, 100%RH), and tidal breathing (600-mL, duty cycle = 33%, 10 breaths/min) was simulated by a servo ventilator (Siemens, model 900C). A filter was located between the distal end of the ETT and test lung to collect the aerosol. Total mass (TM) of salbutamol after 6 respiratory cycles was determined by HPLC-UV spectrophotometry. Similar measurements were undertaken with a Spirale* CHC (Armstrong Medical), providing benchmark data from a European marketed CHC having the pMDI receptacle in-line with the axis of the device. TM (mean ± S.D.) from the AeroVent Plus and Spirale CHCs was 22.7±3.1 and 4.7±0.7 μg/actuation respectively. Clinicians using these devices should be aware of the implications of the difference in drug output between these apparently similar devices.
Nagel et al. (2011) studied this question.