Which mechanism terminates a breath when the target tidal volume is reached?

• A. Flow Cycling
• B. Time Cycling
• C. Exhalation
• D. Volume Cycling

Answer: (D)

Terminating a breath when the target tidal volume is reached is volume cycling. In volume-controlled ventilation, the ventilator is set to deliver a specific tidal volume and tracks the actual air delivered to the patient. When the measured delivered volume reaches the preset target, the inspiratory flow is stopped and the breath ends, allowing exhalation to begin. This approach keeps the amount of air per breath consistent even if airway resistance or lung compliance changes.

If the end of inspiration were based on flow cycling, the breath would end when inspiratory flow falls below a threshold rather than when a volume is delivered. Time cycling ends after a fixed inspiratory time, regardless of how much volume has been delivered. Exhalation is simply the subsequent phase, not the mechanism that ends inspiration.