Valved holding chamber drug delivery is dependent on breathing pattern and device design

Small children with airway obstruction breathe with very low tidal volumes (V(T)) and high respiratory rates (RRs). These extreme respiratory patterns affect drug delivery unpredictably through valved holding chambers (VHCs). We compared in an in vitro study the effectiveness of two VHCs, one small (140 mL, Optichamber Diamond) and one large (350 mL, Babyhaler) without facemasks, to deliver salbutamol to filters positioned between the VHC mouthpieces and a breathing simulator. Different tidal volumes (from 30 mL to 200 mL) and RRs (25·min(-1) and 50·min(-1)) were applied through a breathing simulator. The amount of salbutamol delivered increased with increasing V(T) in both VHCs for both RRs (ρ>0.87 and p<0.001 for both devices at both rates). The effect of RR was not as evident, but drug delivery tended to be higher at the higher rate. Drug delivery was significantly higher through the Optichamber Diamond as compared with the Babyhaler at every combination of RR and V(T) up to a 12-fold difference. We found marked differences in salbutamol delivery between the Babyhaler and Optichamber Diamond VHCs. The delivered dose of salbutamol increased with increasing V(T) and RR with both VHCs but with differences related to valve dead spaces. Instead of considering all VHCs equal in clinical paediatric practice, each device should be tested in vitro with respiratory patterns relevant to small children with respiratory difficulties.