What does Mv (minute ventilation) mean in the context of ventilation?

Minute Ventilation (MV or V̇E): Definition and Clinical Significance

Minute ventilation (MV or V̇E) is the total volume of air exhaled from the lungs in one minute, expressed in liters per minute (L/min). 1

Core Definition and Calculation

V̇E represents the volume of expired air exhaled from the lungs in 1 minute, conventionally expressed in units of liters per minute under BTPS conditions (body temperature, ambient pressure, saturated with water vapor). 1

The calculation is straightforward:

• Minute Ventilation = Tidal Volume × Respiratory Rate 2
• Normal tidal volume: 6-8 mL/kg predicted body weight (approximately 500-600 mL per breath) 2
• Normal respiratory rate at rest: 10-12 breaths per minute 2

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. 3, 2

For a 70 kg adult specifically:

• Total minute volume: 5-7 liters per minute 3
• Mean values in healthy subjects: 6.01 ± 1.39 L/minute 2
• Mean tidal volume: 383 ± 91 mL 2
• Mean respiratory rate: 16 ± 2.8 breaths/minute 2

Exercise and Maximal Values

V̇E max (maximal exercise ventilation) is the highest minute ventilation achieved during a maximal exercise test, usually determined by tests that tax large muscle masses such as cycle ergometry or treadmill. 1

During exercise:

• Oxygen consumption can increase from resting value of approximately 3.5 mL/minute per kilogram to maximum values of 30-50 mL/minute per kilogram (approximately 15 times the resting value) 3
• Athletes can reach values higher than 20 times their resting value 3

Clinical Applications in Mechanical Ventilation

During mechanical ventilation, target tidal volumes of 6-7 mL/kg of ideal body weight to prevent ventilator-induced lung injury while maintaining adequate gas exchange. 3, 2

Key mechanical ventilation principles:

• Use ideal body weight, NOT actual body weight, especially in obese patients 3, 2
• Acceptable tidal volume range: 6-8 mL/kg using ideal body weight 3
• Using actual body weight in obese patients leads to excessive volumes and potential barotrauma 3, 2

Resuscitation Settings

During CPR with an advanced airway, provide ventilation at 8-10 breaths/minute (1 breath every 6-8 seconds) without pausing chest compressions. 3, 2

Critical resuscitation parameters:

• For spontaneous circulation requiring rescue breathing: 10-12 breaths/minute (1 breath every 5-6 seconds) 3, 2
• Do NOT hyperventilate during resuscitation—rates exceeding 12 breaths/minute during CPR decrease cardiac output and worsen outcomes 3, 2

Ventilatory Reserve Assessment

Ventilatory reserve is calculated as (V̇E peak/MVV) × 100, where MVV is maximal voluntary ventilation. 1

• A lower limit of 15% difference between V̇E and MVV represents reasonable reserve based on 95% confidence limits 1
• Patients with pulmonary diseases characteristically have reduced ventilatory capacity and increased ventilatory demand, resulting in reduced ventilatory reserve 1

Related Ventilatory Indices

V̇E/V̇CO₂ (ventilatory equivalent for carbon dioxide) indicates how many liters of air are being breathed to eliminate 1 liter of CO₂, used as a noninvasive estimator of appropriateness of ventilation. 1

V̇E/V̇O₂ (ventilatory equivalent for oxygen) indicates how many liters of air are being breathed for each liter of O₂ uptake. 1

Critical Clinical Pitfalls

Tachypnea (respiratory rate >29 breaths/minute) is an extremely sensitive marker of clinical deterioration in critically ill patients, though nonspecific. 2

Common errors to avoid:

• Never calculate tidal volumes using actual body weight in obese patients 3, 2
• Recognize that breath-to-breath variability is substantial—base measurements on adequate sampling periods (approximately 250 breaths for reproducible results) 2
• In obesity, normalization by height (V̇O₂/height) may be a better correlate of lean body mass than body weight 3