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Effects of Ventilation With Tidal Volume Adjusted on Driving Pressure on Ventilation/Perfusion Ratios and Hemodynamics in ARDS

Sponsor: Assistance Publique - Hôpitaux de Paris

Summary

The driving pressure (DP) is defined as the pressure above the end-expiratory pressure (PEEP) required to distend the respiratory system by the tidal volume (Vt). It is calculated as follows: DP = Plateau pressure - PEEP. It is also equal to the ratio between the tidal volume and the compliance of the respiratory system (Crs): DP = Vt/Crs. Crs is correlated with end-expiratory lung volume, i.e., the lung volume available to receive the tidal volume. DP allows adaptation of the Vt to the available lung volume when the lungs are diseased, rather than to a fraction of lung size when they are healthy, as occurs when tidal volume is adjusted in mL/kg of predicted body weight (PBW). DP is therefore a better reflection of the deformation applied by the tidal volume and the risk of overdistension. It is an important prognostic indicator in acute respiratory distress syndrome (ARDS), with a risk of excess mortality when DP exceeds 14 cm H2O. Conversely, an excessively low DP, suggesting a low tidal volume in relation to the available lung volume, may theoretically also be accompanied by deleterious effects: de-recruitment, atelectrauma, the need to increase respiratory rate, the need for significant sedation, or even curarization. DP and Vt can influence hemodynamics, as overdistension is associated with an increase in dead space and the occurrence of acute cor pulmonale. On the other hand, de-recruitment due to low tidal volume can lead to hypoxic vasoconstriction with an increase in right ventricular afterload.

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