In PC-CMV, what factors determine the tidal volume delivered to the patient?

• A. Patient's age and weight
• B. Compliance and resistance of the lungs, patient effort, and set pressure
• C. Only the set pressure
• D. Type of ventilator used

Answer: (B)

In pressure-controlled continuous mandatory ventilation (PC-CMV), the tidal volume delivered to the patient is primarily influenced by several key factors, which include the compliance and resistance of the lungs, the patient's effort, and the set pressure.

Compliance refers to the ability of the lungs to expand when pressure is applied. Higher compliance means that the lungs can expand more easily, potentially leading to a larger tidal volume for a given pressure. Conversely, low compliance can restrict lung expansion, resulting in a smaller tidal volume.

Resistance reflects how easily air can move through the airways. Increased resistance due to bronchoconstriction, secretions, or obstruction can reduce the tidal volume delivered, even when a set pressure is applied.

The patient's effort is also significant in pressure-controlled ventilation. If a patient spontaneously breathes, their effort can influence the tidal volume delivered, depending on how the ventilator is set to respond to patient-triggered breaths at the predetermined pressure level.

The set pressure is essential in determining the target pressure that the ventilator applies, but the actual volume delivered can vary based on those other factors. Thus, while the set pressure is a component of the equation, it is not the sole determinant of tidal volume in this mode of ventilation.

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