LAUSR

Driving pressure (ΔP), i.e. plateau pressure (Pplat) minus positive end-expiratory pressure, is increasingly a target for limiting inspiratory lung stretch, since it represents the pressure distending the respiratory system. It is commonly thought that estimation of Pplat (and hence ΔP) is unreliable during spontaneous effort because a stable inspiratory “hold” cannot be achieved. Moreover, the contribution of spontaneous effort is ignored if reading airway pressure without esophageal manometry (Pes). Thus, it is thought that Pplat and ΔP are accurately measurable only during paralysis. However, both of these limitations can be easily overcome. First, a brief inspiratory hold during pressure support ventilation (if allowed by the specific ventilator in use, Supplemental Table 1) results in a satisfactory Pplat, as shown in previous publications from our group. Second, inspiratory effort (negative Pes deflection) is not apparent from the airway pressure waveform, but is reflected in it when inspiration is interrupted. An inspiratory hold during a positive pressure breath without spontaneous effort results in a slight decrease in the inspiratory pressure as the flow ceases yielding the Pplat; this is the pressure generated by that static lung volume. An inspiratory hold during a positive pressure breath with spontaneous effort (Fig. 1 and supplemental video) results in an increase in the airway pressure, which is again the Pplat. It is important to realize that this is a true Pplat that reflects the size of the VT and the additional (hidden) contribution of the spontaneous effort. In conclusion, an inspiratory hold during assisted ventilation allows measurement of the total distending