The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

PERFORMANCE COMPARISON OF 4 SPACERS IN A NEONATAL MECHANICAL VENTILATOR-LUNG MODEL.

Jim Keenan BS, RRT, Ralph A. Lugo, PharmD, John W. Salyer BS, RRT, Robert M. Ward, MD. Primary Children's Medical Center and the University of Utah College of Pharmacy, Salt Lake City, Utah.

Introduction: Aerosolized albuterol (ALB) is commonly administered to mechanically ventilated neonates. Many institutions have favored switching from nebulized ALB to metered dose inhalers (MDIs) since the latter is more cost-effective. To administer ALB to intubated neonates via MDI, several in-line spacers are commercially available. Since there are few data in ventilated neonates, we sought to compare the efficiency of ALB delivery using 4 commercially available spacers. Since previous studies in mechanically ventilated neonates have demonstrated limited drug delivery from MDI/spacers, a secondary objective was to determine where ALB is lost and thus unavailable for patient delivery. Methods: The model consisted of a VIP Bird ventilator in a time cycled, pressure-limited, continuous flow mode with ventilator settings selected to simulate a neonate with moderate chronic lung disease: PIP 25 cm H_{2}O, rate 30, Ti 0.35 sec, PEEP 4 cm H_{2}O, FiO_{2} 0.40, flow 9 L/min, T 35° C, and humidified chamber control -1. The test lung compliance was [approx] 0.4 mL/cm H_{2}O and was adjusted with each replicate to obtain a V_{T} of 6.4-6.6 mL. The circuit wye was attached to a 3.0-mm endotracheal tube (ETT) and then to a neonatal test lung. Four spacers were tested in this model (ACE, Aerochamber, Aerovent, and Medspacer) and were placed between the circuit wye and the ETT. A Sims filter (#2832) was placed between the ETT and the test lung to measure ALB delivery to the patient. A second filter was placed between the wye adapter and the expiratory limb to trap aerosolized ALB lost from the spacer via retrograde flow to the expiratory limb. Each of 7 MDIs was actuated 5 times at 30 second intervals, immediately prior to inspiration. After each experiment, filters were rinsed 3 times with 15 mL of filtered water and spacers were rinsed once with 20 mL. Concentrations of ALB in the resultant solutions were analyzed by high performance liquid chromatography, which was determined to be accurate and precise. Results: ALB delivery to the patient, retrograde loss of ALB, and spacer impaction are presented in the table. All values are represented as mean percent of ALB released with each actuation (100 mcg) ± SD.

Spacer Brand Patient Retrograde Spacer Total

ACE 4.1*(0.9) 18.6(3.4) 64.9(6.1) 87.6(7.1)

Aerochamber 1.2(0.5) 26.5(3.1) 66.7(1.8) 94.4(2.9)

Aerovent 1.5(0.3) 16.9(5.6) 83.0(11.3) 101.4(13.9)

Medispacer 2.4?(0.8) 10.9(0.9) 82.9(5.4) 96.2(4.5)

* p < 0.01 for ACE vs. all spacers; ?p < 0.05 for Medispacer vs Aerochamber (ANOVA with Tukey all pairwise comparison).

Conclusion: There were statistically significant and clinically important differences in ALB delivery between 4 commonly used spacers. The ACE spacer demonstrated superior performance when tested with this model. Unanticipated findings included the significant amount of ALB lost to retrograde flow and spacer impaction. Optimizing drug delivery to ventilated neonates may require redesign of in-line spacers to limit drug loss.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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