The configuration of bi-level ventilator circuits may affect compensation for non-intentional leaks during volume-targeted ventilation.

PURPOSE: To assess the behaviour of a pressure-preset volume-guaranteed (V(TG)) mode of ventilation in the presence of non-intentional leaks in single-limb circuit (SLC) home ventilators. METHODS: All SLC home ventilators commercially available in Italy can be used in a V(TG) mode with an intentional leak ("vented") or a true expiratory valve ("non-vented") configuration were selected. Using an experimental model consisting of a mannequin connected to an active lung simulator, for each level of leak (15, 25 and 37 l/min) three different conditions of respiratory mechanics (normal, restrictive and obstructive) were simulated using the ventilators in either a "vented" or "non-vented" configuration. RESULTS: Three home ventilators were tested: Vivo50 (Breas), PB560 (Covidien) and Ventilogic LS (Weimann). In a "vented" circuit configuration all three ventilators kept constant or increased inspiratory pressure in all leak conditions to guarantee the V(TG). Conversely, in a "non-vented" circuit configuration, all tested ventilators showed a drop in inspiratory pressure in all leak conditions, resulting in a concomitant reduction in delivered tidal volume. The same behaviour was found in all conditions of respiratory mechanics. In the absence of leaks, all the ventilators, independently of circuit configuration, were able to maintain the set V(TG) in the presence of modifications of the respiratory mechanics. CONCLUSIONS: The ability of the V(TG) mode to compensate for non-intentional leaks depends strictly on whether a "vented" or "non-vented" circuit configuration is used. This difference must be taken into account as a possible risk when a V(TG) mode is used in the presence of non-intentional leaks.