THE AVL-MODE - A SAFE CLOSED-LOOP ALGORITHM FOR VENTILATION DURING TOTAL INTRAVENOUS ANESTHESIA

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 signif ies automatic breath by breath adaptation of breathing patterns to the lung mechanics of an individual patient. The specific goals are to mi nimize work of breathing, to maintain a preset alveolar ventilation an d to prevent the occurrence of intrinsic PEEP. We ventilated 5 patient s undergoing major abdominal procedures using ALV. ALV was tolerated w ell in all patients. Alveolar ventilation was preset between 5500 and 6500 ml/min. Serial dead space (Vds) and respiratory time constant (re sistence compliance) of the patients ranged from 104 to 164 ml and 0 .74 to 1.5 s, respectively. The resulting respiratory rates ranged fro m 8 to 15 breaths/min, the tidal volumes from 542 to 829 ml, and the a pplied maximum inspiratory pressures from 15.5 to 18.9 mbar. Expirator y 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 patte rns were recorded at values from 7 to 67 s. Overshoot did not reach st atisic significance compared to the variations in breathing patterns w hich occurred during stable measuring periods. Accuracy of the control ler was high (27.8 ml difference between preset and applied alveolar v entilation in the mean) and stability was sufficient for clinical purp oses. The results of this preliminary study show that the breathing pa tterns selected by the controller were well adapted to the lung mechan ics of the patients. Respiratory rates, inspiratory pressures and tida l volumes were within the clinically acceptable range in all patients.