Bench studies evaluating devices for non-invasive ventilation:Critical analysis and future perspectives

Purpose: Because noninvasive mechanical ventilation (NIV) is increasingly used, new devices, both ventilators and interfaces, have been continuously proposed for clinical use in recent years. To provide the clinicians with valuable information about ventilators and interfaces for NIV, several bench studies evaluating and comparing the performance of NIV devices have been concomitantly published, which may influence the choice in equipment acquisition. As these comparisons, however, may be problematic and sometimes lacking in consistency, in the present article we review and discuss those technical aspects that may explain discrepancies. Methods: Studies concerning bench evaluations of devices for NIV were reviewed, focusing on some specific technical aspects: lung models and simulation of inspiratory demand and effort, mechanical properties of the virtual respiratory system, generation and quantification of air leaks, ventilator modes and settings, assessment of the interfaceventilator unit performance. Results: The impact of the use of different test lung models is not clear and warrants elucidation; standard references for simulated demand and effort, mode of generation and extent of air leaks, resistance and compliance of the virtual respiratory system, and ventilator settings are lacking; the criteria for assessment of inspiratory trigger function, inspiration-toexpiration (I:E) cycling, and pressurization rate vary among studies; finally, the terminology utilized is inconsistent, which may also lead to confusion. Conclusions: Consistent experimental settings, uniform terminology, and standard measurement criteria are deemed to be useful to enhance bench assessment of characteristics and comparison of performance of ventilators and interfaces for NIV.