1998 OPEN FORUM Abstracts
EXPIRATORY SYSTEM PERFORMANCE OF THE NPB 840 AND EVITA 4 VENTILATORS DURING PASSIVE EXHALATION
Wayne Johnson RCP, Katie Kinninger RCP, Elzbieta Bak MS, Rick Ford RCP, John Newhart RCP, David Burns MD, UCSD Medical Center, San Diego California
BACKGROUND: This study was designed to assess the performance of the PB 840 (Nellcor Puritan Bennett, Carlsbad, California) and the Evita 4 (Drager, Lubeck, Germany) ventilators during passive exhalation. Methods: The evaluation of the exhalation system characteristics was performed for adult and pediatric ventilator ranges and for two levels of end-expiratory pressure, 0 cmH_{2}O (ZEEP) and 10 cmH_{2}O (PEEP). Both ventilators were configured as specified for patient use and connected to the Vent Aid TTL lung model via adult or pediatric disposable ventilator circuit and endotracheal tube with ID of 7.0 or 4.0 mm. The TTL compliance was set to 50 ml/cmH_{2}O (adult model) or to 10 ml/cmH_{2}O (pediatric model). The ventilator was set to deliver pressure-controlled ventilation with peak pressure of 15 cmH_{2}O above PEEP level. The flow and airway pressures (Paw) were measured at the proximal end of the endotracheal tube. The volume was obtained by numerical integration of the flow. The resistance related energy dissipation (E) during passive exhalation (Marini ARRD 1985; 131:850-854) was used to characterize resistive properties of expiratory valves. The E was calculated as an area enclosed by a plot of exhaled volume against the pressure and normalized to the exhaled tidal volume (V_{T}). Additionally, the fraction of V_{T} remaining in the lung at different expiratory times (Te) was measured as an index of potential air-trapping (Richard, AJRCCM 1998; 157(3):A686).
Results:
ADULT RANGE
Fraction of V_{T} Remaining In Lung at Different
Expiratory Times
(V_{T}-Vexhaled)/ V_{T} (%)
Te ZEEP PEEP Te
EV 4 PB 840 EV 4 PB 840
0.5 45.0 46.3 48.6 50.1 0.3
0.9 14.8 18.2 20.3 24.2 0.5
1.3 0.0 3.1 4.6 10.1 0.7
1.7 0.0 0.0 0.4 4.0 0.9
PEDIATRIC RANGE
Fraction of V_{T} Remaining In Lung at Different
Expiratory Times
(V_{T}-Vexhaled)/ V_{T} (%)
ZEEP PEEP
EV 4 PB EV 4 PB 840
44.0 46.4 51.0 53.6
17.9 20.6 27.7 31.5
1.6 3.2 13.1 16.6
0.3 0.0 4.8 7.5
Energy Dissipation Per Liter of Exhaled Volume
E/V_{T} (J/L)
ZEEP PEEP ZEEP PEEP
EV 4 PB 840 EV 4 PB 840 EV 4 PB EV 4 PB 840
0.769 0.706 0.714 0.702 0.837 0.802 0.764 0.754
Conclusions: Expiratory system of both ventilators showed similar performance during passive exhalation.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.