A Novel, Versatile Valved Holding Chamber for Delivering Inhaled Medications to Neonates and Small Children: Laboratory Simulation of Delivery Options

BACKGROUND: Delivery of bronchodilator to infants and small children from a pressurized metered-dose inhaler with valved holding chamber (pMDI-VHC) is limited by airway narrowness, short respiratory cycle time, and small tidal volume (V_T). There is a need for a versatile, efficient VHC, given the variety of treatment modalities.

METHODS: We tested the AeroChamber Mini VHC (the internal geometry of which is optimized for aerosol delivery, and which accepts a pMDI canister that has a dose counter) in experiments to determine differences in the delivery of hydrofluoroalkane-propelled albuterol (90 μg/actuation) during: mechanical ventilation via endotracheal tube (ETT); manual resuscitation via ETT; and spontaneous breathing via face mask. We tested 5 units of the AeroChamber Mini VHC per test. We simulated the tidal breathing of a premature neonate (V_T 6 mL), a term neonate (V_T 20 mL), and a child approximately 2 years old (V_T 60 mL). We collected the aerosol on an electret filter and quantitatively assayed for albuterol.

RESULTS: The total emitted mass of albuterol per actuation that exited the VHC was marginally greater during spontaneous breathing (12.1 ± 1.8 μg) than during manual resuscitation (10.0 ± 1.1 μg) (P = .046). Albuterol delivery via mechanical ventilation, though comparable with the premature-neonate model (3.3 ± 1.2 μg), the term-neonate model (3.8 ± 2.1 μg), and the 2-y-old-child model (4.2 ± 2.3 μg) (P = .63), was significantly lower than in the spontaneous-breathing and manual-resuscitation models (P < .001). In the neonatal models the total emitted mass was similar with the spontaneous-breathing model (6.0 ± 1.0 μg with the premature-neonate model, 10.5 ± 0.7 μg with the term-neonate model) and the manual-resuscitation model (5.5 ± 0.3 μg premature-neonate model, 10.7 ± 0.9 μg term-neonate model) (P ≥ .46 via one-way analysis of variance).

CONCLUSION: The reduced delivery of albuterol during mechanical ventilation (compared to during spontaneous breathing and manual resuscitation via ETT) was probably associated with the saturated atmosphere in the breathing circuit (37°C, relative humidity > 99%), compared to the ambient air (22 ± 1°C, 44 ± 7% relative humidity). The AeroChamber Mini VHC may provide a versatile alternative to VHCs that are designed exclusively for one aerosol treatment modality.