The effect of unilateral chest drainage for transpulmonary pressure during mechanical ventilation.

Introduction: Chest tube drainage is usually performed through an underwater seal at a level of 10-20 cmH₂O. Based on the definition of transpulmonary pressure, continuous chest drainage creates continuous negative pressure, decreasing pleural surface pressure and increasing transpulmonary pressure. We investigated how unilateral chest drainage could affect the tidal volume or driving pressure during mandatory mechanical ventilation.

Methods: This study was an experimental study using a lung-thoracic model and anesthesia ventilator. Tidal volume was set to 300 mL with pressure-controlled ventilation or volume-controlled ventilation. Left tidal volume and right tidal volume were measured independently using respirometers with positive end-expiratory pressure (PEEP) levels of 0, 10, and 20 cmH₂O. Simultaneously, left negative pressure of the chest drainage was changed to 0, 10, and 20 cmH₂O.

Results: In all conditions, a tidal volume of 300 mL was achieved. In both pressure-controlled ventilation and volume-controlled ventilation, the left tidal volume increased with the application of chest drainage at 10 cmH₂O when the PEEP level was 0 cmH₂O, but left tidal volume decreased with the application of chest drainage at 20 cmH₂O. Furthermore, when PEEP was 10 cmH₂O, the left tidal volume decreased in proportion to the pressure of thoracic drainage. The right tidal volumes changed inversely with their counterpart left tidal volumes.

Conclusion: Unilateral chest drainage caused unbalanced ventilation of the left and right lungs regardless of pressure-controlled ventilation or volume-controlled ventilation.