In a volume-controlled breath, which statement is true about volume and pressure?

• A. The delivered volume is fixed by the ventilator, while pressure may vary with compliance and resistance.
• B. The delivered pressure is fixed, while volume may vary with compliance and resistance.
• C. Both volume and pressure are fixed by ventilator settings.
• D. Volume and pressure both vary randomly with patient effort.

Answer: (A)

In volume-controlled ventilation, you program a specific tidal volume to be delivered with each breath. The ventilator ensures that fixed volume is delivered, assuming no leaks or other issues. The pressure needed to push that volume, however, changes with the patient's lung mechanics. If the lungs are stiff (low compliance) or the airways are narrow or obstructed (high resistance), the ventilator must generate higher airway pressure to deliver the same volume. So volume stays fixed, while pressure varies with compliance and resistance.

That’s why the statement describing the fixed delivered volume with pressure that can vary due to compliance and resistance is the correct one. The idea that pressure is fixed in this mode isn’t accurate, and the notion that both volume and pressure are fixed or that they vary randomly with patient effort isn’t correct for volume-controlled breaths.