What is minute volume?

What is Minute Volume?

Minute volume (also called minute ventilation or V̇E) is the total volume of air exhaled from the lungs in one minute, calculated as tidal volume multiplied by respiratory rate, and expressed in liters per minute. 1

Definition and Calculation

• Minute ventilation = Tidal Volume × Respiratory Rate 2, 3
• The measurement is conventionally expressed in liters per minute (L/min) using BTPS conditions (body temperature, ambient pressure, saturated with water vapor) 1
• This represents the volume of expired air, not inspired air, though they are essentially equivalent under steady-state conditions 1

Normal Values in Healthy Adults

• At rest, normal minute ventilation is approximately 5-7 liters per minute, which corresponds to 70-100 mL/kg/min 2, 4, 3
• For a 70 kg adult, the mean minute ventilation is 6.01 ± 1.39 L/minute 2, 3
• This is derived from:
  • Normal tidal volume: 6-8 mL/kg predicted body weight (approximately 500-600 mL per breath, with a mean of 383 ± 91 mL) 2, 4, 3
  • Normal respiratory rate: 10-12 breaths per minute at rest (with a mean of 16 ± 2.8 breaths/minute) 2, 4, 3

Clinical Significance

During Mechanical Ventilation

• Target tidal volumes should be 6-7 mL/kg of ideal body weight to prevent ventilator-induced lung injury while maintaining adequate gas exchange 2, 4, 3
• Always use ideal body weight, not actual body weight, especially in obese patients to avoid excessive volumes and potential barotrauma 2, 4, 3

During Resuscitation

• During CPR with an advanced airway: provide 8-10 breaths/minute (1 breath every 6-8 seconds) without pausing chest compressions 2, 4, 3
• For spontaneous circulation requiring rescue breathing: provide 10-12 breaths/minute (1 breath every 5-6 seconds) 2, 4, 3
• Avoid hyperventilation (>12 breaths/minute during CPR) as it decreases cardiac output and worsens outcomes 4, 3

Assessment of Ventilatory Function

• Minute ventilation is used to assess ventilatory demand and capacity during exercise testing 1
• Maximal exercise ventilation (V̇E max) is the highest minute ventilation achieved during maximal exercise testing 1
• Ventilatory reserve is calculated as (V̇E peak/MVV) × 100, where a lower limit of 15% difference represents reasonable reserve 2

Important Clinical Pitfalls

• Measurement conditions matter significantly: Minute ventilation measured during room air breathing can be 20-25% higher than when measured with supplemental oxygen (11.0 vs 13.5 L/min), potentially leading to inappropriate deferral of weaning trials 5
• Mouthpiece use artificially alters breathing pattern: Using a mouthpiece increases tidal volume by 34%, decreases breathing frequency by 10%, and increases minute ventilation by 16% 6
• Breath-to-breath variability is substantial: Measurements should be based on adequate sampling periods (approximately 250 breaths) for reproducible results 3
• Tachypnea (>29 breaths/minute) is an extremely sensitive marker of clinical deterioration in critically ill patients, though it is nonspecific 3

Related Ventilatory Indices

• Ventilatory equivalent for CO₂ (V̇E/V̇CO₂): Indicates how many liters of air are breathed to eliminate 1 liter of CO₂, used as a noninvasive estimator of ventilation appropriateness 1, 2
• Ventilatory equivalent for O₂ (V̇E/V̇O₂): Indicates how many liters of air are breathed for each liter of O₂ uptake 1, 2