Question

In volume cycled respiration the inspiratory flow rate is set at:

• A. 140-160 L/min
• B. 110-130 L/min
• C. 60-100 L/min
• D. 30-50 L/min

Hint:

Volume cycled ventilators are usually run at a moderate inspiratory flow of about 60-100 L/min.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
In volume cycled ventilation, the ventilator delivers a preset tidal volume to the patient during each breath, and it does this at a chosen inspiratory flow rate, the speed at which gas is pushed into the lungs. We need to know the usual range this flow rate is set at.

Step 2: Key Formula or Approach:
The inspiratory flow rate has to be fast enough to deliver the full tidal volume within a reasonable inspiratory time, without being so fast that it creates high peak airway pressure or turbulent, uneven gas flow to the lungs. Anaesthesia ventilators are set within a moderate practical range that balances these two needs.

Step 3: Detailed Explanation:
140-160 L/min and 110-130 L/min are both too fast for routine volume cycled ventilation. Flows this high push gas in abruptly, raising peak airway pressure and giving poor, uneven distribution of the breath within the lungs.
30-50 L/min sits at the low end and can work for gentle ventilation, but on its own it may not be enough to deliver an adequate tidal volume within a normal inspiratory time in many adult patients, so it is not the standard range quoted for this setting.
60-100 L/min is the range that comfortably delivers the set tidal volume within a normal inspiratory time while keeping airway pressures and gas turbulence in a safe zone. This is the range commonly used for volume cycled ventilation in practice.

Step 4: Final Answer:
The inspiratory flow rate in volume cycled respiration is usually set at 60-100 L/min, option 3.