Background: Noninvasive ventilation (NIV) is increasingly used in intensive care medicine, but only little information is available how different NIV interfaces affect the performance of a ventilatory system. Therefore, we compared delay times, pressure time products (PTPs), and wasted efforts during inspiration among patients receiving invasive ventilation and NIV with a helmet (NIV-h) or a face mask (NIV-fm).
Methods: Using an in vitro lung model capable of simulating spontaneous breathing, gas flow and airway pressure were measured with varying positive end-expiratory pressure and pressure support (PS) levels. Wasted efforts were determined while lung compliance, respiratory rate (RR), continuous positive airway pressure (CPAP), and PS levels were changed.
Results: Delay times were more than twice as long with a helmet compared to NIV-fm or invasive ventilation (p < 0.001), but decreased during NIV-h with increasing CPAP (p < 0.001) and PS levels (p < 0.001). During the initial inspiratory phase, PTP was smaller with NIV-h compared to NIV-fm or invasive ventilation, but not so when a complete inspiration with PS was evaluated. Wasted efforts occurred earlier during NIV-h and were aggravated with rising PS, RR, and compliance.
Conclusions: Although delay times are prolonged during NIV-h, PTP is initially smaller compared to NIV-fm and invasive ventilation, indicating less work of breathing due to the high volume the patient can access. Increasing the CPAP or PS level decreases delay times in NIV-h and should therefore be considered whenever possible. Wasted inspiratory efforts occurred at higher RRs and should carefully be monitored during NIV.