Ventilator-induced lung injury (VILI) can occur despite use of tidal volume (VT) limited to 6 ml/kg of predicted body weight, especially in patients with a smaller aerated compartment (i.e. the baby lung) in which, indeed, tidal ventilation takes place. Because respiratory system static compliance (CRS) is mostly affected by the volume of the baby lung, the ratio VT/CRS (i.e. the driving pressure, ΔP) may potentially help tailoring interventions on VT setting.
Driving pressure is the ventilatory variable most strongly associated with changes in survival and has been shown to be the key mediator of the effects of mechanical ventilation on outcome in the acute respiratory distress syndrome. Observational data suggest an increased risk of death for patients with ΔP more than 14 cmH2O, but a well tolerated threshold for this parameter has yet to be identified. Prone position along with simple ventilatory adjustments to facilitate CO2 clearance may help reduce ΔP in isocapnic conditions. The safety and feasibility of low-flow 2 removal">extracorporeal CO2 removal in enhancing further reduction in VT and ΔP are currently being investigated.
Driving pressure is a bedside available parameter that may help identify patients prone to develop VILI and at increased risk of death. No study had prospectively evaluated whether interventions on ΔP may provide a relevant clinical benefit, but it appears physiologically sound to try titrating VT to minimize ΔP, especially when it is higher than 14 cmH2O and when it has minimal costs in terms of CO2 clearance.
aInterdepartmental Division of Critical Care Medicine, University of Toronto
bKeenan Centre for Biomedical Research, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Canada
cDepartment of Anesthesiology and Intensive Care Medicine, Catholic University of the Sacred Heart
dFondazione ‘Policlinico Universitario A. Gemelli’, Rome, Italy
eService de Pneumologie et Réanimation, Département ‘R3S’ Groupe Hospitalier Pitié Salpêtrière - Charles Foix, Assistance Publique Hôpitaux de Paris
fSorbonne Université, UPMC University Paris 06, INSERM, UMRS1158 Neurophysiology Respiratoire Expérimentale et Clinique, Paris, France
Correspondence to Laurent Brochard, Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada. Tel: +1 416 864 686; fax: +1 416 864 5698; e-mail: BrochardL@smh.ca