1998 OPEN FORUM Abstracts
TIDAL VOLUME, AUTOPEEP AND INSPIRATORY TIME RESPONSE OF BILEVEL PRESSURE VENTILATORS (BPV) TO A RANGE OF IMPEDANCE CONDITIONS.
Pete Bliss BME, Robert McCoy RRT, Alexander Adams RRT. Regions Hospital, St. Paul, MN.
Background: Noninvasive ventilation, as delivered by BPV, is being administered to avoid tracheal intubation and as a form of chronic ventilatory support. While volume-cycled ventilators deliver a set tidal volume (VT), bilevel devices deliver volume determined by the set pressure, inspiratory flow profile, expiratory trigger setting and response to the respiratory system impedance condition. BPV have not been tested extensively and may not respond well to adverse or changing respiratory system impedance conditions. We hypothesized that delivered VT would be predictable within a range of impedance conditions and consistent between BPV at similar settings. Method: We constructed a bench model system for testing triggered breaths on a mechanical test lung (TTL- Michigan Instruments). Three BPV in common use (BiPAP S/T-D30 - Respironics, 335 - Nellcor-PB, Quantum - Healthdyne) were tested at IPAP 15 cmH2O, EPAP3 cmH2O, f = 10/min. Their volume delivery capabilities were challenged by combinations of linear resistance (R) (5,20,50 cmH2O/L/sec) and compliance (C) (.02, .05, .08, .11 L/cmH2O). We also measured autoPEEP, Ti, and flow and pressure waveforms for the various conditions. Results: Tidal volume delivery for the tested devices (VT - ml):
R/C .02 .05 .08 .11 .02 .05 .08 .11
5 224 581 896 1127 210 546 789 1030
20 222 468 607 662 214 473 629 699
50 201 301 328 338 214 351 326 361
R/C .02 .05 .08 .11
5 207 429 615 792
20 131 222 323 388
50 134 161 164 182
Tidal volume decreased in response to decreasing compliance and increasing resistance for each BPV but more so for the Quantum. AutoPEEP developed for C=.11/R=50 for the BiPAP and 335 (4.3, 4.2, respectively) associated with higher VT, an increased Ti and decreased Te compared to the Quantum.
Conclusions: BPV had a wide range of VT response to the tested impedance conditions. Although the response was somewhat predictable, differences between expiratory trigger algorithms and inspiratory flow profiles partially account for differences between devices. Monitoring of adequate supported ventilation by BPV must be scrupulous under adverse and changing impedance conditions.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.