1999 OPEN FORUM Abstracts

ALBUTEROL DELIVERY FROM MDI AND SPACER IS REDUCED FOLLOWING SHORT DURATION MANUAL VENTILATION IN A NEONATAL VENTILATOR-LUNG MODEL.

Ralph A. Lugo PharmD, Julie Ballard BS, RRT, Keith Elkins BS, University of Utah College of Pharmacy and School of Medicine, Primary Children's Medical Center, Salt Lake City, Utah.

BACKGROUND: Aerosolized albuterol (ALB) is commonly administered to mechanically ventilated neonates with chronic lung disease. Treatment with a metered dose inhaler (MDI) and spacer is more efficient and less costly than nebulization; however, prolonged use of large-volume spacers in neonates may result in CO₂ retention due to mechanical dead space. To minimize this risk, some institutions limit the time that spacers remain in-line to < 30 seconds. However, this strategy may also limit ALB delivery. The objective of this bench study was to determine the relationship between the time that a spacer is left in place following each MDI actuation and the efficiency of ALB delivery in a neonatal ventilator-lung model.

Methods: The model consisted of a Bird VIP ventilator in a time cycled, pressure-limited, continuous flow mode with settings to simulate a 1-kg infant with moderate lung disease. The circuit was attached to a 3.0-mm endotracheal tube (ETT) and a neonatal test lung. Ventilator settings: Vt = 6.5-6.7 mL, flow 9 L/min, pressure 25/4 cm H₂O, rate 30, FiO2 0.4, and gas conditioned to 34°C. There were five methods of administration tested (see table) following two actuations of ALB MDI (VentolinÒ). The first three methods utilized an ACEÒ spacer attached to the ETT followed by 5, 15, and 30 manual breaths after each actuation (anesthesia bag-flow 6 L/min, rate 30, PIP 25 cm H2O). The final two methods utilized an in-line ACEÒ spacer (placed between the circuit wye and ETT) with the spacer kept in-line for 30 sec and 60 sec after each actuation. A breathing filter was placed between the ETT and test lung to trap aerosolized albuterol. Filters were rinsed with 50 ml of 50% methanol solution and ALB concentration was analyzed chromatographically by HPLC (99.1% accuracy and CV <3.3%, n=9).

Results: Mean (SD) ALB delivery (%) is presented below. Thirty manual breaths after each actuation increased ALB delivery by 44% and 118% as compared to 15 and 5 manual breaths, respectively. Inserting the spacer in-line and waiting 60 seconds after each actuation improved ALB delivery by 59% as compared to 5 manual breaths after each actuation.

CONCLUSION: Manually ventilating for 30 breaths after each actuation resulted in a superior ALB delivery as compared to 15 breaths and 5 breaths. Similar results can be achieved by leaving the spacer in-line for 30-60 seconds after each actuation.

OF-99-208