Abstract
BACKGROUND: The precision of quasi-static airway driving pressure (ΔP) assessed in pressure support ventilation (PSV) as a surrogate of tidal lung stress is debatable because persistent muscular activity frequently alters the readability of end-inspiratory holds. In this study, we used strict criteria to discard excessive muscular activity during holds and assessed the accuracy of ΔP in predicting global lung stress in PSV. Additionally, we explored whether the physiological effects of high PEEP differed according to the response of respiratory system compliance (C(RS)). METHODS: Adults with ARDS undergoing PSV were enrolled. An esophageal catheter was inserted to calculate lung stress through transpulmonary driving pressure (ΔP(L)). ΔP and ΔP(L) were assessed in PSV at PEEP 5, 10, and 15 cm H(2)O by end-inspiratory holds. C(RS) was calculated as tidal volume (V(T))/ΔP. We analyzed the effects of high PEEP on pressure-time product per minute (PTP(min)), airway pressure at 100 ms (P(0.1)), and V(T) over PTP per breath (V(T)/PTP(br)) in subjects with increased versus decreased C(RS) at high PEEP. RESULTS: Eighteen subjects and 162 end-inspiratory holds were analyzed; 51/162 (31.5%) of the holds had ΔP(L) ≥ 12 cm H(2)O. Significant association between ΔP and ΔP(L) was found at all PEEP levels (P < .001). ΔP had excellent precision to predict ΔP(L), with 15 cm H(2)O being identified as the best threshold for detecting ΔP(L) ≥ 12 cm H(2)O (area under the receiver operating characteristics 0.99 [95% CI 0.98-1.00]). C(RS) changes from low to high PEEP corresponded well with lung compliance changes (R(2) 0.91, P < .001) When C(RS) increased, a significant improvement of PTP(min) and V(T)/PTP(br) was found, without changes in P(0.1). No benefits were observed when C(RS) decreased. CONCLUSIONS: In subjects with ARDS undergoing PSV, high ΔP assessed by readable end-inspiratory holds accurately detected potentially dangerous thresholds of ΔP(L). Using ΔP to assess changes in C(RS) induced by PEEP during assisted ventilation may inform whether higher PEEP could be beneficial.