How does SIMV differ from assist-control ventilation?

• A. SIMV provides synchronized mandatory breaths with spontaneous breaths between; assist-control delivers breaths at a set rate, with patient effort augmenting or triggering breaths.
• B. SIMV provides breaths at a fixed rate only; assist-control provides spontaneous breaths.
• C. SIMV uses pressure support only; assist-control uses volume control only.
• D. SIMV is manual ventilation; assist-control is automated.

Answer: (A)

The main idea is how breaths are delivered and how patient effort is treated. In SIMV, there is a set of breaths delivered in synchronization with the patient, but between those mandatory breaths the patient can take spontaneous breaths that are not assisted by the ventilator. This means the patient can contribute to ventilation, and the number of mandatory breaths per minute is fixed while spontaneous breaths add variability.

In assist-control ventilation, every breath is delivered with full support at a set rate, and patient effort can trigger breaths as well. Whether the breath is patient-triggered or time-triggered, the ventilator provides a consistent tidal volume (or pressure) for that breath, so the patient’s effort augments the timing but not the amount of support.

So, the described statement aligns with SIMV providing synchronized mandatory breaths with spontaneous breaths between, while assist-control delivers breaths at a set rate with patient effort augmenting or triggering breaths.