Abstract
The purpose was to develop a bench setup for testing a decision support system (DSS) for proportional assist ventilation (PAV). The test setup was based on a patient simulator connected to a mechanical ventilator with the DSS measurement sensors connected to the respiratory circuit. A test case was developed with parameters of lung mechanics reflecting a patient with mild acute respiratory distress syndrome. Five experiments were performed starting at different levels of percentage support (%Supp) and continuing until the DSS advised to remain at current settings. Final advice ranged from %Supp of 50-70%, indicating some dependence of baseline level, but with resulting patient effort estimates indicating that this may not be clinically important. Further studies are required of test cases reflecting different patient types and in patients.
Highlights
Setting mechanical ventilation can be considered as an optimization problem of balancing competing goals
The decision support system (DSS) includes mechanistic steady state models of pulmonary gas exchange, mechanics, drive and blood acidbase status. These models can be identified from a single arterial blood gas measurement entered into the DSS and measurements of pressures and settings from the ventilator collected via RS-232 communication, in combination with DSS built in continuous oxygenation measurements by pulse oximetry and side-stream breath-by-breath calorimetry giving flows, volumes, respiratory rate (RR), O2 and CO2 levels as well as metabolism (VO2 and VCO2) [4]
All other work of breathing (WOB) estimates decreased with increasing support level, except the Pmus,peak estimate which primarily showed a change when increasing support from 50 to 70 and 80% which resulted in decreased Pmus,peak
Summary
Setting mechanical ventilation can be considered as an optimization problem of balancing competing goals. In supported ventilation modes where patients’ spontaneous efforts trigger ventilator support, one important tradeoff is to the correct levels of support to avoid both under-support, which may cause inappropriately high work of breathing (WOB) [1], and over-support, which can depress respiratory drive and cause atrophy of the respiratory muscles [2]. The system has been shown to provide appropriate advice in patients on controlled mechanical ventilation and pressure support ventilation [5,6]. Proportional Assist Ventilation (PAV) is a mechanical ventilation mode for patients with spontaneous breathing efforts [7]. PAV has resulted in similar WOB as pressure support [8] but improved patient-ventilator synchrony [9]
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