AN ADAPTIVE LUNG VENTILATION CONTROLLER

Closed loop control of ventilation is traditionally based on end-tidal or mean expired CO2. The controlled variables are the respiratory rat e RR and the tidal volume V-T. Neither patient size or lung mechanics were considered in previous approaches. Also the modes were not suitab le for spontaneously breathing subjects. This report presents a new ap proach to closed loop controlled ventilation, called Adaptive Lung Ven tilation (ALV), ALV is based on a pressure controlled ventilation mode suitable for paralyzed, as well as spontaneously breathing, subjects. The clinician enters a desired gross alveolar ventilation (V-gA' in 1 /min), and the ALV controller tries to achieve this goal by automatic adjustment of mechanical rate and inspiratory pressure level. The adju stments are based on measurements of the patient's lung mechanics and series dead space. The ALV controller was tested on a physical lung mo del with adjustable mechanical properties. Three different lung pathol ogies were simulated on the lung model to test the controller for rise time (T-90), overshoot (Y-m), and steady state performance (Delta max ). The pathologies corresponded to restrictive lung disease (similar t o ARDS), a ''normal'' lung, and obstructive lung disease (such as asth ma). Furthermore, feasibility tests were done in 6 patients undergoing surgical procedures in total intravenous anesthesia. In the model stu dies, the controller responded to step changes between 48 seconds and 81 seconds. It did exhibit an overshoot between 5.5% and 7.9% of the s etpoint after the step change. The maximal variation of V-gA' in stead y state was between +/-4.4% and +/-5.6% of the setpoint value after th e step change. In the patient study, the controller maintained the set V-gA' and adapted the breathing pattern to the respiratory mechanics of each individual patient.