Author: Clinical Experts Group, Hamilton Medical
Date of first publication: 02.04.2020
Last change: 02.04.2020First published: 02.06.2017 Reference 6 changed from abstract to publication, additional data added
As the aerated lung has normal compliance, the reduction in respiratory system compliance is mainly due to the non-aerated part of the lung, and can serve as an estimation of the end-expiratory lung volume. In turn, the ratio between tidal volume and end-expiratory lung volume represents the strain applied to the lung. Therefore, the ratio between tidal volume and respiratory system compliance – also called driving pressure (ΔP) – can be considered a substitute for lung strain. Driving pressure is calculated as the difference between plateau pressure and total PEEP, and can be measured quite easily using end-inspiratory and end-expiratory occlusions respectively.
A multilevel mediation analysis of individual pooled data from 2,365 ARDS patients included in four randomized controlled trials showed that ΔP was the ventilator variable associated most strongly with hospital survival. Any change in tidal volume or PEEP affected the outcome only when associated with a decrease in ΔP (
A large observational study aimed at better understanding the global impact of acute respiratory failure (the LUNG SAFE study) was conducted in 459 intensive care units in 50 countries around the world. Results showed that ARDS occurs in 10% of all patients admitted to the ICU, with a hospital mortality of 40% (
These results, however, should not be seen as implying that tidal volume is of no importance for lung protection. Most of the patients included in this study did indeed receive low tidal volumes. What the study does show is that when a low tidal volume is used, ΔP is an important variable to monitor for assessing the risk of hospital mortality. Although there is no data from prospective randomized controlled studies available to provide strong recommendations as to what the ΔP should be, it would seem reasonable to advocate keeping ΔP below 14 cmH2O.
There are several methods available for limiting ΔP, such as muscle relaxants, use of the prone position, decreasing instrumental dead space, veno-venous extracorporeal CO2 removal, and ECMO (
Adaptive Support Ventilation (ASV®) and INTELLiVENT®-ASV (
Airway driving pressure is associated with clinical outcomes in ARDS, post-surgical, and normal-lung patients, and is a measure of the strain applied to the respiratory system and the risk of ventilator-induced lung injuries. Evidence suggests we should keep driving pressure below 14 cmH2O. But how can we measure it?