LAUSR

Initial correspondence from Drs. Taylor and Camporota Dear Editor, We congratulate Zhou and colleagues on an insightful trial [1]. The authors reported that driving pressure (∆P) in the airway pressure release ventilation (APRV) arm was similar to that in the low tidal volume (LTV) arm (12.6 vs. 12.3 cmH2O, respectively) at day 3. However, we feel that ∆P may have been overestimated in the APRV arm. As stated in note (d) of Table 2, ∆P in the APRV arm was calculated by switching to a volume-controlled mode and then subtracting the previous monitoring PEEP from the plateau pressure. This ignores the contribution of expiratory pressure (analogous to intrinsic PEEP) present at the end of the release phase. As demonstrated below, the total expiratory pressure can be estimated—giving a better estimate of true ∆P (Fig. 1). The authors calculated the expiratory time constant (τ) for all patients on APRV using the following equation: