Abstract
Adherence to low tidal volume (VT) ventilation and selected positive end-expiratory pressures are low during mechanical ventilation for treatment of the acute respiratory distress syndrome. Using a pig model of severe lung injury, we tested the feasibility and physiological responses to a novel fully closed-loop mechanical ventilation algorithm based on the “open lung” concept. Lung injury was induced by surfactant washout in pigs (n = 8). Animals were ventilated following the principles of the “open lung approach” (OLA) using a fully closed-loop physiological feedback algorithm for mechanical ventilation. Standard gas exchange, respiratory- and hemodynamic parameters were measured. Electrical impedance tomography was used to quantify regional ventilation distribution during mechanical ventilation. Automatized mechanical ventilation provided strict adherence to low VT-ventilation for 6 h in severely lung injured pigs. Using the “open lung” approach, tidal volume delivery required low lung distending pressures, increased recruitment and ventilation of dorsal lung regions and improved arterial blood oxygenation. Physiological feedback closed-loop mechanical ventilation according to the principles of the open lung concept is feasible and provides low tidal volume ventilation without human intervention. Of importance, the “open lung approach”-ventilation improved gas exchange and reduced lung driving pressures by opening atelectasis and shifting of ventilation to dorsal lung regions.
Highlights
Using a closed-loop feedback algorithm for mechanical ventilation, our key findings are that (a) the OLA algorithm allows for fully automated mechanical ventilation without any human intervention in severely lung injured pigs by (b) successfully providing lung protective mechanical ventilation and that (c) application of the automatized “open lung approach” results in high PaO2/FIO2-ratios and low driving pressures in conjunction with dorsal lung recruitment and ventilation
Second and with regards to the selection of positive end-expiratory pressure (PEEP), our data show that with application of a fully computer controlled “open lung” approach, the absolute level of positive end expiratory pressure was higher as compared to the Acute Respiratory Distress Syndrome (ARDS) Network PEEP/FIO2 table and higher as compared to our previous closed loop ARDSNet algorithm [6]
When comparing the recent findings to a previously published closed loop ARDSNet algorithm, we find that the open lung protocol leads to higher P aO2/ FIO2-ratios and significant reduction of lung driving pressures via dorsal recruitment and ventilation of the lung [6]
Summary
The Acute Respiratory Distress Syndrome (ARDS) Network landmark study proved that application of physiological principles translate into highly significant mortality reduction in patients suffering from ARDS [1]. A recent secondary analysis of human studies applying higher than traditional PEEP values to maintain injured lungs open and prevent cyclic alveolar collapse and reopening, indicates increased survival for patients responding to higher PEEP with increased oxygenation of arterial blood [3].
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