How does Assist Control (AC) ventilation differ from SIMV?

Assist Control (AC) ventilation is characterized by delivering full tidal volumes for each breath, whether initiated by the patient or the ventilator. This mode assists patients who may not be able to maintain adequate ventilation on their own by ensuring that every breath they take—or that is triggered by the ventilator—is of a preset volume. This approach maximizes tidal volume delivery and provides consistent ventilation, making it a supportive choice for patients with compromised respiratory function.

In contrast, SIMV (Synchronized Intermittent Mandatory Ventilation) allows patients to breathe spontaneously between the mandatory breaths delivered by the ventilator. While SIMV provides assistance, the tidal volume of spontaneous breaths is not guaranteed to match the preset ventilator settings, which is a distinction from AC ventilation. In AC, the ventilator guarantees the delivery of full tidal volumes for both assisted and spontaneous breaths, thereby enhancing patient ventilation without relying on the patient’s effort alone to achieve sufficient tidal volume.

This fundamental characteristic of delivering all breaths as full tidal volumes under AC distinguishes it from other methods of ventilation and highlights its role in supporting patients with reduced respiratory drive or effort.