Jornal Brasileiro de Pneumologia | 2021
Caring for patients at risk of ARDS: the role of driving pressure
Abstract
1. Disciplina de Pneumologia, Departamento de Cardiopneumologia, Instituto do Coração – InCor – Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo (SP) Brasil. 2. Instituto de Ensino e Pesquisa, Hospital Sírio-Libanês, São Paulo (SP) Brasil. Lung-protective strategies in patients with ARDS on mechanical ventilation (MV) are associated with reduced mortality.(1-3) Adherence to these strategies has improved progressively over the last two decades, because increasing numbers of physicians and respiratory therapists have come to recognize lung protection as the cornerstone of supportive therapy.(4) Lung-protective strategies represent a bundle of interventions to reduce lung injury aggravated by MV itself, known as ventilator-induced lung injury. These strategies usually aim to apply low tidal volumes (4-6 mL/kg of predicted body weight), low plateau pressures (< 30 cmH2O), and enough PEEP to reach oxygenation goals. The rationale is to avoid lung overdistension and to minimize the mechanical stress imposed on the lungs, which are the primary pathophysiological mechanisms of ventilator-induced lung injury.(5) Recently, airway driving pressure (expressed as the difference between plateau pressure and PEEP) has been proposed as the primary variable that can be targeted in order to avoid lung injury. The idea is that limiting driving pressure can be safer in patients with injured lungs. In such patients, the size of the functional aerated lung can be considerably small, a baby lung, to borrow the term coined by Gattinoni et al.(6) The application of tidal volumes normalized to predicted body weight takes into account the size of the patient but not the size of the baby lung, which ends up being overdistended and overstressed.(7) Driving pressure is nothing more than tidal volume normalized to respiratory system compliance, which has been shown to follow closely the size of the functional lung.(8) A patient-level meta-analysis of trials involving patients with ARDS showed that lower driving pressures were associated with improved survival.(9) More importantly, the survival benefit of protective MV strategies was mediated by driving pressures, not by tidal volume or PEEP.(9)