Intro:

The mortality of acute respiratory distress syndrome (ARDS) remains high (40%), and may be aggravated by ventilation-induced lung injury (VILI), the main mechanisms of which are:

1. Anterior region overdistension,
2. Atelectrauma in the posterior regions. Positive expiratory pressure (PEEP) adjusted on the ventilator during ARDS aims to recruit posterior pulmonary territories in order to limit atelectrauma but is accompanied by a concomitant risk of overdistension of anterior territories.

Recent data suggest that continuous anterior chest compression (CACC) could limit the overdistension of the anterior regions by decreasing the compliance of the anterior chest wall and thus the regional transpulmonary pressure, while promoting the redistribution of ventilation to the posterior territories.

The effects of CCAC on ventilation/perfusion ratios and hemodynamics are unknown.

Hypothesis/Objective :

The participants hypothesize that during ARDS, CCAC:

1. Improves ventilation/perfusion ratios by decreasing both anterior territory dead space effect and posterior territory shunt,
2. Induce an improvement in cardiac output by decreasing right ventricular afterload (decrease in capillary compression related to the overdistension of the anterior territories and decrease in hypoxic vasoconstriction of the condensed territories).

Objective:

Primary outcome :

To evaluate the effects of CCAC on ventilation/perfusion ratios during moderate to severe ARDS.

Secondary outcome :

To evaluate the effects of CCAC on hemodynamics : left heart morphology, systolic and diastolic function, cardiac output, right heart morphology, systolic function, pulmonary hypertension, volemia.

Method In patient with moderate to severe ARDS, CACC is performed manually and the pressure applied will be maintained between 60 and 80 cmH2O.

Electrical impedance tomography of ventilation and perfusion will be used for the measurement of the percentage of areas with normal VA/Q ratios, areas of shunt and areas of dead space effect.

Left heart morphology, systolic and diastolic function, cardiac output, right heart morphology, systolic function, pulmonary hypertension, volemia will be evaluated by using echocardiography.

Inclusion Criteria:

• Age ≥ 18 years
• ARDS moderate to severe according to the Berlin criteria
• Patient receiving continuous sedation and curarization
• Free and informed consent from the patient or family member

Exclusion Criteria:

• Pregnancy
• Adult patient subject to a legal protection measure (tutor, curator, etc.)
• Patients with a pacemaker, automatic implantable cardioverter defibrillator,
• Contraindications to thoracic belt placement (e.g., thoracic or spinal cord trauma, recent thoracic surgery)
• Undrained pneumothorax, bronchopleural fistula
• Hemodynamic instability (i.e., use of intravenous fluids of more than 10 mL/kg or vasopressors 2 mg/h of norepinephrine or 0.5 mg/h of epinephrine)

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