Chest
Volume-Assured Pressure Support Ventilation (VAPSV): A New Approach for Reducing Muscle Workload during Acute Respiratory Failure
Section snippets
The VAPS Device
VAPSV essentially can be conceived as a form of volume-cycled ventilation. In other words, the ventilator is designed to stop the inspiratory phase only after a preset tidal volume is delivered to the patient. During this inspiratory period, two flow sources will be working in parallel: one with a fixed square wave-flow pattern (a high impedance source), which is able to deliver a constant flow (CF, adjustable from 10 up to 120 L/min) whatever the airway pressure may be; and another one, a
RESULTS
The respiratory variables measured after 40 min of ventilation with VAV and VAPSV are presented in Table 2. A significant decrease in the work parameters (WOB/L, WOB/min, and PTPb-see Fig 2 and 3) and in the ventilatory drive (P0.1tr) was achieved during the VAPSV period. At the same time, a significant improvement of some mechanical parameters (Cdyn, rs, VT/TI, and Irs) was observed.
Figure 4 shows that there was an evident relationship (r = 0.99) between the level of work performed by each
DISCUSSION
The main finding of this study is that the ventilatory workload imposed on the inspiratory muscles during VAV was significantly reduced by the use of VAPSV. All three work parameters studied—WOB/L, WOB/min, and PTPb—were reduced to half or less in most of our patients. Also, those patients performing the more distressed ventilation during VAV—in view of their impaired pulmonary mechanics and high levels of ventilation requirements—were just those presenting the greater reductions in their
APPENDIX A
When we were performing the initial tests with the VAPS device, we observed that the shape of the inspiratory flow curve during VAPSV had important mechanical consequences. A well-adjusted VAPSV was normally characterized by a decreasing flow tracing resembling conventional PSV, with the consequent benefits of an increased VT/TI, a reduced peak tracheal pressure, and the best values of dynamic compliance and inspiratory impedance (see Fig 2, on the right). This flow pattern was necessarily
ACKNOWLEDGMENT
The authors wish to thank Rosangela Santoro de Souza Amato for her assistance in the manuscript and to Intermed-Equipamento Hospitalar Ltda for its dedication and technical assistance.
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This work was presented in part at the 36th Congress of the AARC, New Orleans, December 8-11, 1990. (Abstract published in Respiratory Care 1990; 35[11]:1113)
Supported by the Laboratório de Investigaçã o Médica and Instituto do Coraçã o—HC-FMUSP; FAPESP; COOPERSUCAR; and Intermed-Equipamento Medico Hospitalar Ltda.