1997 OPEN FORUM Abstracts
TIDAL VOLUME DELIVERY VARIABILITY FOR THREE NONINVASIVE BILEVEL POSITIVE PRESSURE (BPP) DEVICES.
Bliss P. Adams A. Healthpartners-St. Paul Ramsey Medical Center. St. Paul, MN.
Background: The use of noninvasive ventilation has been described and recommended for avoiding intubation in the settings of impending respiratory failure, assisting in the weaning process and providing ventilatory support for chronic respiratory failure. Several devices are available for non-invasive ventilation featuring simplified controls and at less cost than critical care ventilators. While differences between critical care ventilators exist, the gas delivery characteristics at their standard settings is considered precise and predictable between ventilators. We evaluated 3 BPP devices at similar settings to determine variability in tidal volume (VT) delivery between and within devices. Methods: The BPP devices (Nellcor-Puritan Bennett 335 (NPB), BIPAP STD, Healthdyne Quantum) were sequentially tested on one lung of a Michigan lung model system (Grand Rapids, MI) at IPAP = 15 cmH2O, EPAP = 3 cmH2O and various available trigger and rise time settings. A ventilator driving the other lung triggered efforts by a lift arm. An open, fixed orifice was interposed to simulate a leaking mask. Flow was measured by a Hans-Rudolph pneumotach and Validyne MP-45 transducer. Data was acquired and flow was integrated to attain VT measurements from 10 breaths by LabTech software (National Instruments). Results: Differences in VT between and within devices are shown below.
Device and settings Max Min Average S. D. C. V.
NPB 335 1/1 (insp/exp trigger) 842 666 774 50 6.4%
NPB 335 3/3 (insp/exp trigger) 920 895 909 9 0.9%
BiPAP STD 890 877 885 4 0.5%
Quantum .1 rise time 499 459 485 11 2.2%
Quantum .5 rise time 609 591 603 6 1.0%
Quantum .9 rise time 678 631 650 14 2.2%
At the same general settings VT delivery varied between devices and in the same device at different trigger or rise time settings. Variability for a device at the same setting was minimal as noted by low coefficients of variation. The patterns of flow delivery differed, visually, between and within devices according to trigger and rise time differences. Conclusions: To assure comparable performance between devices a practitioner must be aware of the level and meaning of trigger and rise time settings. Even when adjustments are made, it may be difficult to substitute devices to accomplish precisely the same task. Performance characteristics varied between and within devices in this lung model study, however, we can not comment on the ability of BPP devices to meet specific intended clinical purposes. Supported by the Ramsey Foundation.