The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

Evaluation of Three Small Volume nebulizers for use with Infant Ventilator Circuits

 

Kristin Smith AS, RRT1,2, Tom Blackson BS, RRT1,3, Tim Cox BS, RRT2, Thomas H. Shaffer Ph.D.2, 4. 1Delaware Technical & Community College, 2AI duPont Hospital for Children, 3Christiana Care Health System, 4Nemours Lung Center, DE


Background:
Aerosolized medication delivery is common in mechanically ventilated neonates. We have previously demonstrated that the flow needed to power a conventional small volume nebulizer (SVN) can cause several adverse patient conditions such as altered volume delivery and patient-ventilator dyssynchrony in the spontaneously triggering infant. Metered dose inhalers may obviate the need for SVN devices in some, but not all, situations. New nebulizer technology is currently available that is intended for use with infants receiving mechanical ventilation.

Purpose: To compare three SVN devices and their impact on ventilation parameters and patient-ventilator synchrony during continuous flow nebulization with infant mechanical ventilation.

Materials and Methods: A Servo 300 ventilator (S300) (Siemens, Danvers, MA) was used to ventilate a double bellows test lung (Michigan Instruments, Grand Rapids, MI) driven by an LTV-1000 (Pulmonetics, Minneapolis, MN) to simulate an infant spontaneously breathing 40 B/min. Three different nebulizers were used for comparison: a Mistyneb conventional SVN (Allegiance, McGaw Park, IL), a miniHEART SVN (Westmed Inc, Tucson, AZ), and the Aeroneb Pro (Aerogen, Sunnyvale, CA). Airway resistance was created using a 2.5mm ID endotracheal tube (ETT) (Malinkrodt, Pleasanton, CA) and lung compliance was set at 1 ml/cm H2O. The SVN devices were tested with the S300 in the pressure control/SIMV mode. Ventilator settings were the same for all test conditions: frequency (f): 30 B/min, inspiratory time (TI): 0.4 seconds, PEEP: 4 cm H2O, peak inspiratory pressure (PIP): 15 cm H2O above PEEP, pressure support level (PSV): 10 cm H2O above PEEP, and sensitivity set to the most sensitive flow trigger setting without auto-triggering. The LTV was adjusted to insure that each spontaneous effort was sensed by the S300 during control conditions (C) resulting in a PSV supported inspiration. An unaltered infant circuit was used for the C. Three test conditions were evaluated: the Aeroneb Pro was operated electronically according to the manufacturer's recommendations (#1), 6 L/min of flow was used to power the Mistyneb (#2), and 2 L/min powered the miniHEART (#3). All nebulizers were placed in the inspiratory limb of the C circuit at the temperature probe adapter. VT, f, minute volume (MV), PIP, PEEP, and TI measurements were made using a CO2SMO differential pressure transducer (Novametrix, Wallingford, CT) placed between the ventilator circuit and the ETT (independently displayed values-IDV) for the C and all test conditions. 

RESULTS:
The MV, VT spontaneous (VTS), TI, PIP, and PEEP were significantly different in conditions #2 and #3 compared to the C (p<0.05). These parameters were unaltered in condition #1 relative to the C (p>0.05). 

  MV total (L) VT S (ml) TI (sec.) PIP (cm H2O) PEEP (cm H2O)
Control (SD) 0.38 (0.01) 6.10 (0.00) 0.37 (0.11) 18.67 ( 2.32) 4.51 (0.04)
#1 Aerogen (SD) 0.37 (0.01) 6.11 (0.03) 0.38 (0.12) 18.70 ( 2.32) 4.47 (0.05)
#2 Mistyneb (SD) 0.47 (0.02) 1.49 (0.08) 0.48 (0.13) 31.77 (10.34) 5.90 (0.07)
#3 MiniHEART (SD) 0.33 (0.02) 1.62 (0.04) 0.50 (0.16) 19.31 ( 5.81) 4.86 (0.05)


CONCLUSION:
Compared to the control, condition #1 resulted in the least alteration in set ventilation parameters and patient-ventilator synchrony. Decreased VTS and increased TI during conditions #2 and #3 reflect patient-ventilator dyssynchrony not evident during condition #1. 

Clinical Implications: The Aerogen nebulizer, condition #1, alleviates the problems associated with flow added by either a conventional or miniHEART SVN in this test model. Clinical correlation with this bench model is indicated. 

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