The AVL-mode: A safe closed loop algorithm for ventilation during total intravenous anesthesia

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Abstract
The Adaptive Lung Ventilation Controller (ALV-Controller) represents a new approach to closed loop control of ventilation. It is based on a pressure controlled ventilation mode. Adaptive lung ventilation signifies automatic breath by breath adaptation of breathing patterns to the lung mechanics of an individual patient. The specific goals are to minimize work of breathing, to maintain a preset alveolar ventilation to prevent the occurrence of intrinsic PEEP. We ventilated 5 patients undergoing major abdominal procedures using ALV. ALV was tolerated well in all patients. Alveolar ventilation was preset between 5500 and 6500 ml/min. Serial dead space (Vds) and respiratory time constant (resistence* compliance) of the patients ranged from 104 to 164 ml and 0.74 to 1.5 s, respectively. The resulting respiratory rates ranged from 8 to 15 breaths/min, the tidal volumes from 542 to 829 ml, and the applied maximum inspiratory pressures from 15.5 to 18.9 mbar. Expiratory time was sufficient in all cases to allow complete expiration and to avoid intrinsic PEEP. I: E-relations ranged from 0.36 to 0.76. After a step change in alveolar ventrilation rise times of the breathing patterns were recorded at values from 7 to 67 s. Overshoot did not reach statisic significance compared to the variations in breathing patterns which occurred during stable measuring periods. Accuracy of the controller was high (27.8 ml difference between preset and applied alveolar ventilation in the mean) and stability was sufficient for clinical purposes. The results of this preliminary study show that the breathing patterns selected by the controller were well adapted to the lung mechanics of the patients. Respiratory rates, inspiratory pressures and tidal volumes were within the clinically acceptable range in all patients.

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