title: Experts' opinion on management of hemodynamics in ARDS patients: focus on the effects of mechanical ventilation.
abstract: BACKGROUND
  Acute respiratory distress syndrome (ARDS) is frequently associated with hemodynamic instability which appears as the main factor associated with mortality. Shock is driven by pulmonary hypertension, deleterious effects of mechanical ventilation (MV) on right ventricular (RV) function, and associated-sepsis. Hemodynamic effects of ventilation are due to changes in pleural pressure (Ppl) and changes in transpulmonary pressure (TP). TP affects RV afterload, whereas changes in Ppl affect venous return. Tidal forces and positive end-expiratory pressure (PEEP) increase pulmonary vascular resistance (PVR) in direct proportion to their effects on mean airway pressure (mPaw). The acutely injured lung has a reduced capacity to accommodate flowing blood and increases of blood flow accentuate fluid filtration. The dynamics of vascular pressure may contribute to ventilator-induced injury (VILI). In order to optimize perfusion, improve gas exchange, and minimize VILI risk, monitoring hemodynamics is important.
  
  
  RESULTS
  During passive ventilation pulse pressure variations are a predictor of fluid responsiveness when conditions to ensure its validity are observed, but may also reflect afterload effects of MV. Central venous pressure can be helpful to monitor the response of RV function to treatment. Echocardiography is suitable to visualize the RV and to detect acute cor pulmonale (ACP), which occurs in 20-25 % of cases. Inserting a pulmonary artery catheter may be useful to measure/calculate pulmonary artery pressure, pulmonary and systemic vascular resistance, and cardiac output. These last two indexes may be misleading, however, in cases of West zones 2 or 1 and tricuspid regurgitation associated with RV dilatation. Transpulmonary thermodilution may be useful to evaluate extravascular lung water and the pulmonary vascular permeability index. To ensure adequate intravascular volume is the first goal of hemodynamic support in patients with shock. The benefit and risk balance of fluid expansion has to be carefully evaluated since it may improve systemic perfusion but also may decrease ventilator-free days, increase pulmonary edema, and promote RV failure. ACP can be prevented or treated by applying RV protective MV (low driving pressure, limited hypercapnia, PEEP adapted to lung recruitability) and by prone positioning. In cases of shock that do not respond to intravascular fluid administration, norepinephrine infusion and vasodilators inhalation may improve RV function. Extracorporeal membrane oxygenation (ECMO) has the potential to be the cause of, as well as a remedy for, hemodynamic problems. Continuous thermodilution-based and pulse contour analysis-based cardiac output monitoring are not recommended in patients treated with ECMO, since the results are frequently inaccurate. Extracorporeal CO2 removal, which could have the capability to reduce hypercapnia/acidosis-induced ACP, cannot currently be recommended because of the lack of sufficient data.
authors.affiliation: Intensive Care Unit, Section Thorax-Vascular Disease-Abdomen-Metabolism, Service de Réanimation, Assistance Publique-Hôpitaux de Paris, University Hospital Ambroise Paré, 9, avenue Charles de Gaulle, 92100, Boulogne-Billancourt, France. antoine.vieillard-baron@apr.aphp.fr.|University of Versailles Saint-Quentin en Yvelines, Faculty of Medicine Paris Ile-de-France Ouest, 78280, Saint-Quentin en Yvelines, France. antoine.vieillard-baron@apr.aphp.fr.|INSERM U-1018, CESP, Team 5 (EpReC, Renal and Cardiovascular Epidemiology), UVSQ, 94807, Villejuif, France. antoine.vieillard-baron@apr.aphp.fr.
authors.forename: A
authors.initials: A
authors.lastname: Vieillard-Baron
authors.affiliation: Departments of Medicine and Anesthesia and the Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Matthay
authors.affiliation: Assistance Publique-Hôpitaux de Paris, Hôpitaux universitaires Paris-Sud, Hôpital de Bicêtre, service de réanimation médicale, Le Kremlin-Bicêtre, France.|Université Paris-Sud, Faculté de médecine Paris-Sud, Inserm UMR S_999, Le Kremlin-Bicêtre, France.
authors.forename: J L
authors.initials: JL
authors.lastname: Teboul
authors.affiliation: Department of Anesthesia, Operative Intensive Care, University Hospital Regensburg, 93042, Regensburg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Bein
authors.affiliation: Laboratory of Experimental Intensive Care and Anesthesiology, Department of Intensive Care, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Schultz
authors.affiliation: Department of Critical Care, McGill University Health Centre (Glen Site Campus), Montreal, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Magder
authors.affiliation: Departments of Pulmonary and Critical Care Medicine, University of Minnesota and Regions Hospital, Minneapolis/St. Paul, MN, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Marini
mesh_terms: D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008991:Monitoring, Physiologic; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D012307:Risk Factors
keywords: ARDS; Echocardiography; Guidelines; Heart–lung interactions; Hemodynamic monitoring; Shock