Volume–controlled home ventilators were the first machines used to deliver NPPV, mostly for a domiciliary care. Even if well equipped with alarms, monitoring system, and inner battery, their usefulness to apply NPPV is largely limited by their inability to compensate for air leaks. Consequently, their NPPV application is today restricted to home-based selected cases of neuromuscular disorders, although they still play a role in the safe invasive support of ventilatory-dependent tracheostomized patients [3].

Bi–level ventilators are the evolution of home-based continuous positive airway pressure (CPAP) devices and derive their name from their capability of supporting spontaneous breathing with two different pressures: an inspiratory positive airway pressure (IPAP) and a lower expiratory positive airway pressure (EPAP) or positive end-expiratory pressure (PEEP). These machines were specifically designed to deliver NPPV, thanks to their efficiency in compensating air leaks. Because of their easy handling, transportability, lack of alarms and monitoring system, and low costs, the first generation of bi-level ventilators matches the needs for nocturnal NPPV in chronic patients with a large ventilatory autonomy. However, traditional bi-level ventilators showed important technical limitations (risk of CO₂ rebreathing due to their single-limb circuit in non-vented masks; inadequate monitoring; lack of alarms and O₂ blending; limited generating pressures; poor performance to face the increase in respiratory system load, lack of battery), which have been largely overcome by more sophisticated machines. The newer generations of bi-level ventilators have gained popularity in clinical practice to apply acute NPPV, especially in higher levels of care settings, as well as to invasively support ventilatory-dependent chronic patients at home. These new devices are capable of delivering a large extent of more advanced pressometric modalities of ventilation, with the inclusion of “hybrids modes” such as volume-target pressure-preset ventilation (i.e., volume-assured pressure support ventilation, or VAPS), which can dynamically change the level of pressure assistance depending on the measured tidal volume according to different algorithms. Despite their physiological benefits, the real clinical advantages of these “hybrids modes” have yet to be demonstrated compared with the traditional pressometric modalities [3, 4].

ICU ventilators were initially designed to deliver invasive ventilation via a cuffed endotracheal tube or tracheal cannula to either sick patients in the intensive care unit (ICU) or to allow surgical procedures in the theatre room. Despite good monitoring of ventilatory parameters and of flow-pressure-volume waves, as well as a satisfactory setting of FiO₂ and of ventilation, performance of conventional ICU ventilators in delivering NPPV is poor because they are not able to cope with leaks. Thus, a new generation of ICU ventilators has been developed to efficiently assist acute patients with NPPV with to the option of leak compensation (i.e., “NPPV mode”), which allows a partial or total correction of air leak-induced patient-ventilator asynchrony, even with large intermachine variability [5].

Intermediate ventilators combine some features of bi-level, volume-cycled, and ICU ventilators (dual-limb circuit, sophisticated alarm and monitoring systems, inner battery, both volumetric and pressometric modes, wide setting of inspiratory and expiratory parameters). “Hybrid modes” of ventilation, such as VAPS, are available with the great majority of newer intermediate ventilators. These new machines are designed to meet the patients’ needs, both at home and in the hospital, and for the safe transport of critically ill patients [3, 4].