Variable Ventilation Is Equally Effective as Conventional Pressure Control Ventilation for Optimizing Lung Function...

Area of Science:

• Critical Care Medicine
• Respiratory Physiology
• Mechanical Ventilation

Background:

• Conventional mechanical ventilation (CMV) can be monotonous.
• Introducing variability, such as mathematically derived variability (MVV) or physiological breathing pattern variability (PVV), has been proposed to improve lung recruitment and gas exchange.
• The efficacy of these variable ventilation strategies in acute respiratory distress syndrome (ARDS) remains unclear.

Purpose of the Study:

• To compare the effects of PVV, MVV, conventional pressure-controlled ventilation with sighs (PCS), and conventional pressure-controlled ventilation without sighs (PCV) in a rabbit model of severe ARDS.
• To evaluate the impact of two positive end-expiratory pressure (PEEP) levels (6 and 9 cmH2O) on respiratory mechanics and gas exchange under different ventilation modes.

Main Methods:

• Severe ARDS was induced in 54 anesthetized rabbits via lung lavage, endotoxin, and injurious ventilation.
• Rabbits were randomly assigned to PVV, MVV, PCV, or PCS for 5 hours at either 6 or 9 cmH2O PEEP.
• Ventilation parameters, blood gas indices, respiratory mechanics (tissue damping G, elastance H), serum cytokine levels, and lung histology were assessed.

Main Results:

• PVV and PCV at 6 cmH2O PEEP did not show progression of lung injury.
• PCS and MVV at 6 cmH2O PEEP resulted in worsening of lung mechanics (G, H) and gas exchange (PaCO2, pH).
• Higher PEEP (9 cmH2O) improved lung function and reduced inflammation across all ventilation modes, irrespective of the pattern.

Conclusions:

• PVV provided protection against lung injury progression comparable to PCV in moderate PEEP settings.
• MVV and PCS were associated with adverse effects on lung mechanics, potentially due to increased peak inspiratory pressures.
• Increasing PEEP is a more significant factor for improving respiratory mechanics and gas exchange in severe ARDS than the choice of ventilation mode.