In this issue of Respiratory Care, Vargas et al present the results of a randomized study comparing neurally-adjusted ventilatory assist (NAVA) versus variable pressure support (VPS) ventilation.1 The goal was to evaluate the effect of both modes on synchrony and work of breathing. The study was carefully planned, and a fair amount of information is given for us to review and compare. At the end, no major differences were found. To the reader, this may seem as just another trial with evidence of no difference. However, there are many details, based on how the modes work and are tested, that can give perspective to their results.
A mode of ventilation is a predetermined pattern of patient-ventilator interaction that can be classified by 3 characteristics: (1) control variable, that is, pressure or volume; (2) breath sequence, that is, continuous mandatory ventilation, intermittent mandatory ventilation, or continuous spontaneous ventilation; and (3) targeting scheme(s).2 Such taxonomy is important for distinguishing arbitrary brand names from generic classifications, just as is done in pharmacology. Once taxonomy aspects are standardized, it is easier to evaluate performance in terms of clinical outcomes (eg, mortality), technological features serving the goals of ventilation (ie, safety, comfort, and liberation),3 patient-ventilator interaction (ie, synchrony issues),4 and/or discrete physiological outcomes (eg, work of breathing). Vargas et al1 focused on compared physiological outcomes (synchrony and work of breathing) between NAVA and VPS. Their study allows us to discuss a framework to compare modes. Evidently, modes differ substantially with respect to technical capabilities as well as settings used to manage them. Thus, a systematic comparison of mode characteristics could help understand differences and potential sources of bias when assessing performance. Table 1 summarizes a construct to assess the differences between NAVA and VPS with pressure support …
