The Science Journal of the American Association for Respiratory Care
Background: Aerosolized albuterol (ALB) is commonly administered to mechanically ventilated neonates via MDI and spacer. Most manufacturers recommend placing spacers in the inspiratory limb, immediately proximal to the circuit wye. This location may be impractical during neonatal ventilation due to continuous flow and difficulty in adapting spacers to the circuit. Thus, practitioners often place spacers between the wye and endotracheal tube (ETT). However, large-volume spacers introduced at this location may result in CO2 retention due to mechanical dead space. The objective of this bench study was to determine the relationship between CO2 accumulation in an ACE® spacer and the time that a spacer remains in-line between the wye and the ETT. In addition, we sought to determine the effect of different tidal volumes on CO2 accumulation.
Methods: The model consisted of a Bird VIP ventilator in a time cycled (rate 20), pressure-limited, continuous flow (7L/min) mode. The circuit wye was attached to an ACE
Results: Data are represented as mean (SD) end-tidal CO2 (mm Hg) for each 30 second interval (n=30).
|9 mL VT||15 mL VT||25 mL VT|
|0-30 sec||0||0.18 (0.70)||0.95 (1.54)|
|31-60 sec||1.78 (1.19)||2.98 (1.12)||6.38 (1.36)|
|61-90 sec||3.90 (0.92)||4.75 (0.72)||7.48 (1.31)|
|91-120 sec||4.98 (0.80)||5.68 (0.87)||6.75 (1.92)|
|121-150 sec||6.30 (0.79)||5.98 (0.80)||7.32 (1.90)|
|151-180 sec||6.79 (0.94)||6.48 (0.71)||6.68 (1.56)|
CONCLUSION: Accumulation of CO2 within the spacer increased with time and reached a maximum of 6-7 mm Hg in this model. Due to the short duration of spacer use when administering drugs via MDI, this level of CO2 exposure is likely clinically insignificant for the majority of ventilated newborns.