What is the compression factor for the described ventilator circuit delivering 750 mL at 10/min with 6 L/min measured ventilation and 30 cm H2O peak pressure?

What is the compression factor for the described ventilator circuit delivering 750 mL at 10/min with 6 L/min measured ventilation and 30 cm H2O peak pressure?

• A. 1 mL (cm H2O)-1
• B. 3 mL (cm H2O)-1
• C. 4 mL (cm H2O)-1
• D. 5 mL (cm H2O)-1

Answer: (D)

Circuit compressibility is the volume stored in the breathing circuit as it is pressurized, so part of the gas delivered by the ventilator doesn’t reach the patient. The compression factor measures how many milliliters are compressed per centimeter of water pressure. Here, the ventilator delivers 750 mL per breath, but the patient receives 6 L/min at a rate of 10 breaths/min, which is 600 mL per breath. The extra volume that goes into compressing the circuit is 750 − 600 = 150 mL per breath. With a peak inspiratory pressure of 30 cm H2O, the amount of volume compressed per cm H2O is 150 mL / 30 cm H2O = 5 mL per cm H2O. So the compression factor is 5 mL (cm H2O)−1.

Circuit compressibility is the volume stored in the breathing circuit as it is pressurized, so part of the gas delivered by the ventilator doesn’t reach the patient. The compression factor measures how many milliliters are compressed per centimeter of water pressure.

Here, the ventilator delivers 750 mL per breath, but the patient receives 6 L/min at a rate of 10 breaths/min, which is 600 mL per breath. The extra volume that goes into compressing the circuit is 750 − 600 = 150 mL per breath. With a peak inspiratory pressure of 30 cm H2O, the amount of volume compressed per cm H2O is 150 mL / 30 cm H2O = 5 mL per cm H2O.

So the compression factor is 5 mL (cm H2O)−1.