Volume-controlled Ventilation Does Not Prevent Injurious Inflation during Spontaneous Effort

Area of Science:

• Respiratory physiology
• Mechanical ventilation
• Lung injury research

Background:

• Spontaneous breathing during mechanical ventilation can increase transpulmonary pressure and tidal volume (Vt), potentially exacerbating lung injury.
• Controlling Vt and transpulmonary pressure is intuitively thought to mitigate injury from spontaneous effort.

Purpose of the Study:

• To test if volume-controlled ventilation limits Vt and transpulmonary pressure, resulting in less injurious inflation patterns during spontaneous effort in injured lungs.

Main Methods:

• Dynamic computed tomography in rabbits with injured lungs to assess regional inflation patterns.
• Esophageal balloon manometry to estimate transpulmonary pressure (Pl(es)) with and without spontaneous effort.
• Intrapleural manometry to estimate local dependent lung stress.
• Electrical impedance tomography in a pig and an ARDS patient.

Main Results:

• Spontaneous breathing increased Pl(es) during pressure-controlled ventilation but not volume-controlled ventilation.
• Volume-controlled ventilation with spontaneous effort led to greater dorsal lung inflation and recruitment compared to muscle paralysis, despite similar Vt and Pl(es).
• Higher local dependent lung stress, underestimated by esophageal manometry, was observed during spontaneous effort.

Conclusions:

• Volume-controlled ventilation's limitation of Vt and Pl(es) did not fully prevent harm from spontaneous breathing.
• Reducing spontaneous effort and local dependent lung stress is necessary to eliminate injury.