Evaluation of adaptive support ventilation in paralysed patients and in a physical lung model

Objective: Evaluation of the respiratory pattern selected by the Adaptive Support Ventilation (ASV) in ventilated patients with acute, chronic respiratory failure and normal lungs and in a physical lung model. Design: We tested ASV both on patients and in a physical lung model, with a normal level of minute ventilation and with minute ventilation increased by 30%. In each patient, respiratory pattern, mechanics and blood gases were recorded. Setting: General ICU of a University Hospital. Results: In patients with normal lungs, mean values+/-SD were: tidal volume (Vt) 558.1 +/- 142.4mL, respiratory rate (RR) 12.6 +/- 1.3b/min and inspiratory time/total time ratio (Ti/Ttot) 42.4 +/- 4.1%; in COPD, mean values +/- SD were: Vt 724 +/- 171mL, RR 9.2 +/- 2.7b/min and Ti/Ttot 26.6 +/- 10.5%; in restrictive ones, mean values SD were: Vt 550.2 +/- 77.0mL, RR 15.8 +/- 2.6b/min, Ti/Ttot 47.5 +/- 2.5%. In the lung model, at a normal setting, mean values +/- SD were: Vt 523 +/- 18.5mL, RR 14 +/- 0.0b/min, Ti/Ttot 44.0%, in COPD, mean values SD were: Vt 678 +/- 0.0mL, RR 9 +/- 0.0b/min, Ti/Ttot 20 +/- 0.7%, in restrictive one, mean values SD were: Vt 513 +/- 12.8mL, RR 15 +/- 0.0b/min, Ti/Ttot 48 +/- 1.5%. In model hyperventilation conditions in a normal setting a Vt of 582 +/- 16.6mL, RR 16 +/- 0.0b/min, Ti/Ttot 48 +/- 0.0% were selected, in the obstructive setting Vt 883 +/- 0.0mL, RR 0 +/- 0.0b/min, Ti/Ttot 20 +/- 0.0% and in a restrictive one Vt 545 +/- 8.4mL, RR 18 +/- 0.0b/min, Ti/Ttot 50 +/- 0.0%. Conclusions: In normal patients ASV selected a ventilatory pattern close to the physiological one, in COPD almost a high expiratory time pattern and in restrictive ones a reduced tidal volume pattern. In the model the selection was similar. In the hyperventilation test, ASV chose a balanced increase in both Vt and RR.