Minute Ventilation (Tidal Volume × Respiratory Rate)

Minute ventilation is the total gas moved into the lungs each minute, and it is simply the volume of one breath times the number of breaths. A resting adult at 500 mL a breath and 12 breaths a minute moves $500 \times 12 = 6000$ mL/min, or 6 L/min. On a ventilator the two terms are set directly, which makes this the first calculation anyone learns in critical care.

The important thing the number hides is dead space. Roughly 150 mL of each breath never reaches an alveolus; it sits in the trachea and bronchi and gets exhaled unchanged. So of that 6 L/min, only $(500 - 150) \times 12 = 4200$ mL/min actually participates in gas exchange. That distinction matters enormously when you change the settings. Doubling the rate at half the tidal volume keeps minute ventilation at 6 L/min but collapses alveolar ventilation to $(250 - 150) \times 24 = 2400$ mL/min, and the patient's CO₂ climbs even though the headline number never moved. Rapid shallow breathing is inefficient for exactly this reason.

Because CO₂ clearance tracks alveolar ventilation almost exactly, this calculation is the lever for managing an arterial CO₂. It is much less useful for oxygenation, which depends on inspired oxygen fraction and on mean airway pressure rather than on how much gas moves. And the tidal volumes chosen in practice are set by lung-protective targets based on predicted body weight, typically 6 to 8 mL/kg, not by whatever minute ventilation looks tidy.