The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts


PRECISION OF TIDAL VOLUME (VT) DELIVERED DURING VOLUME-TARGETED VENTILATION IN A SPONTANEOUSLY BREATHING NEONATAL LUNG MODEL WITH DIFFERENT NEONATAL VENTILATORS.



John Salyer, RRT, Cary Jackson RRT. Respiratory Care Service, Children's Hospital and Regional Medical Center, Seattle Washington.

Introduction
: Neonatal ventilators now offer modes of ventilation with VT -targeting using decelerating flow profiles. Each manufacturer has different programming to respond to changes in the patient's pulmonary mechanics. Infant breathing has been shown to be very erratic, e.g. wide variations in VT (Am J Perinatol 1999;16:549-59). We sought to determine how well these ventilators maintain these targeted volumes in the presence of erratic spontaneous neonatal breathing.

Methods
: We used the Ingmar Active Servo Lung 5000 (ASL 5000) simulator to mimic neonatal breathing. The simulator allows programming of individual breaths or groups of breaths. The spontaneous breathing model was 196 seconds in length, including epochs of apnea, eupnea, and tachypnea, with varying TI and VT. The table at left describes the exact conditions of the test lung, including the length of time of each epoch. VT generated by the lung simulator was measured with a pneumotachometer and data acquisition software placed at the connection to the lung simulator (Cosmo Plus and Analysis Plus, Novametrix Inc.). The rates and volumes selected for each epoch were based on a combination of the published literature and our experience. Ventilators tested included Viasys Avea, Drager Baby Log and Evita XL, Puritan Bennet PB 840, & Maquet Servo-i. The Servo-i was tested twice, at the manufacturer's request, after new software revisions were released that were supposed to improve neonatal volume accuracy. Thus, Servo-i-1 is with the older software, while the Servo-i-2 is with the newer software. Volume-limiting on the Avea was activated and set at 6 mL. Each ventilator was set up with a conventional dual heated wire circuit to give VT = 5 mL in their respective modes for VT-targeted ventilation, with decelerating flow. Mean differences with tested with ANOVA with significance established as P < 0.05.

Results
: The figure at left shows distributions of VT for each ventilator. Differences between distributions were both clinically important and statistically significant, P < 0.0001.
Test Lung Conditions
Time Rate TI VT
24 30 0.4 4.3
15 100 0.2 1.8
6 0 0 0
15 80 0.3 1.4
12 20 0.4 4.3
12 10 0.45 2.8
7.5 0 0 0
6 100 0.2 6.7
15 40 0.35 5.4
12 20 0.4 4.3
15 100 0.2 1.8
6 0 0 0
15 80 0.3 1.3
12 20 0.4 4.4
9 100 0.2 4.3
15 20 0.4 3.3
Time and TI in seconds



Discussion
: The Avea clearly kept the VT much closer to the targeted VT than any of the other ventilators. This was achieved in part through the use of their unique volume-limiting feature. This allows the user to set a VT limit, which the ventilator will not exceed, even if the patient tries to take a larger breath. This feature could lead to flow starvation and/or patient agitation and should be used with prudence and studied further.
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PRECISION OF TIDAL VOLUME (VT) DELIVERED DURING VOLUME-TARGETED VENTILATION IN A SPONTANEOUSLY BREATHING NEONATAL LUNG MODEL WITH DIFFERENT NEONATAL VENTILATORS.