The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts


M. D. Babic1, R. L. Chatburn1, J. K. Stoller1

Background: The Vortran Automatic Resuscitator (VAR) has been suggested as an emergency ventilator. The purpose of this study was to test the hypothesis that changing the simulated patient load connected to the VAR will have a significant effect on minute alveolar ventilation.

The VAR was connected to a passive lung model and loads representative of ventilated patients were imposed. Tidal volume (VT), frequency, inspiratory time, expiratory time, peak inspiratory pressure and autoPEEP were measured. Duty cycle (%I) minute ventilation (MV), minute alveolar ventilation (MVA) and estimated PaCO2 were calculated. Data were analyzed using standard design of experiments (DOE) procedures including ANOVA. P values < 0.05 were considered significant.

Assuming the lung model represented an adult weighing 68 kg, the VT ranged from a low of 1.7 mL/kg to a high of 16.7 mL/kg. The %I was 30% at 40 L/min and 52% at 20 L/min source gas flow. As the load increased, the VT decreased and the frequency increased. MVA ventilation ranged from zero to 9.8 L/min, resulting in a calculated PaCO2 of over 100 torr to 16 torr, respectively. DOE analysis showed that VT was affected independently by compliance and resistance (p < 0.001 and p < 0.05, respectively). Frequency was affected only by compliance (p < 0.001). MVA increases as compliance increases and/or resistance decreases (p < 0.001 and p < 0.01, respectively). The table below shows the average of the 3 VARs tested.

The VAR automatically increases frequency and decreases tidal volume resulting in inappropriate levels of minute alveolar ventilation over a range of compliance and resistance expected for paralyzed patients ventilated for respiratory failure. Variable performance and the lack of alarms prompt caution in using the VAR for emergency situations where patients cannot be constantly monitored by trained and experienced operators. We suggest that use of the VAR in the management of a patient with ARDS would be ill-advised and potentially unsafe. The major limitation of this study was that we simulated a passive patient. A patient who was able to trigger the VAR could presumably maintain a more consistent minute alveolar ventilation and gas exchange. We made no effort to increase the tidal volume by adjusting PIP (and decrease frequency) as the load increased. Our results should be generalized only to patients unable to trigger inspiration and unattended by trained operators.