Airway and Transpulmonary Driving Pressure by End-Inspiratory Holds During Pressure Support Ventilation

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 H₂O 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 H₂O. 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 H₂O being identified as the best threshold for detecting ΔP_L ≥ 12 cm H₂O (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 (R² 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.

Keywords: acute respiratory distress syndrome; interactive ventilatory support; patient monitoring; respiratory mechanics; ventilator-induced lung injury.

Fig. 1.

Airway pressure (P_aw), esophageal pressure (P_es), transpulmonary pressure (P_L), and flow tracing during an end-inspiratory hold performed during pressure support ventilation. As can be observed, there is a first part of the inspiratory hold where P_aw, P_es, and P_L waveforms are flat and readable. Contrarily, at the end of the hold, a new inspiratory effort occurs, making all measurements unreadable from that point onward. P_aw = airway pressure; ΔP = airway driving pressure; P_es = esophageal pressure; P_L = transpulmonary pressure; ΔP_L = transpulmonary driving pressure.

Fig. 2.

Association between airway and transpulmonary driving pressure assessed in pressure support ventilation at different PEEP levels. ΔP_L = transpulmonary driving pressure; ΔP = airway driving pressure.

Fig. 3.

Accuracy of airway driving pressure to detect transpulmonary driving pressure ≥ 12 cm H₂O. The black dot in the left-upper corner of the curve indicates the best cut-off point according to Youden index.

Fig. 4.

Individual physiological response of subjects who increased (right panels) and decreased (left panels) respiratory system compliance with high PEEP. (A) work of breathing, (B) respiratory drive, (C) neuromuscular ventilatory coupling. C_RS = respiratory system compliance; PTP_min = pressure-time product per minute; P_0.1 = airway pressure decay during the first 100 ms of an expiratory occlusion; V_T/PTP_br = relationship tidal volume and pressure-time product per each breath; In (A), the scale of y axis was rescaled by square root function to improve visualization.