Volume targeted pressure support ventilation (VT-PSV) is a hybrid mode increasingly used to maintain a minimal tidal volume (VT) by automatically adjusting the level of inspiratory pressure. The objective of the study was to determine the ability of home ventilators to maintain the preset minimal VT during unintentional leaks in a VT-PSV mode.
Methods
Seven ventilators were tested on a lung bench with different circuit configurations and with different levels of unintentional leaks. Unintentional leaks were generated using calibrated holes.
Results
All the studied ventilators with a single-limb circuit with intentional leak (n = 5) were able to maintain the minimal preset VT during unintentional leaks. One ventilator overcompensated VT during unintentional leaks of high intensity. In contrast, all studied ventilators with a single circuit with an expiratory valve (n = 2) or a double-circuit (n = 3) but one failed to maintain the minimal VT during unintentional leaks. Unintentional leaks generated a decrease in inspiratory pressure, which was responsible for the fall in VT.
Conclusions
Most of the studied ventilators with a single-limb circuit with intentional leak correctly estimate the expiratory VT and therefore successfully maintain the preset minimal VT during unintentional leaks, in contrast to most of the studied ventilators with a double-circuit, which paradoxically are not able to directly measure expiratory VT. Importantly, the VT-PSV mode, when used with most ventilators with expiratory valve or double-circuit, can paradoxically exacerbate the VT drop during unintentional leaks.
