Evaluation of Adaptive Support Ventilation in Paralysed Patients and in a Physical Lung Model

Abstract

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 9±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.