Which of the following is NOT a primary mode of ventilation?

Continuous Positive Airway Pressure (CPAP) mode is not considered a primary mode of ventilation because it primarily serves to maintain airway patency and support oxygenation rather than actively provide mechanical ventilation. In CPAP mode, the patient initiates all breaths, and the ventilator does not deliver any mandatory breaths. It helps keep the alveoli open during expiration and ensures adequate oxygen delivery but does not assist with the mechanics of breathing like the other modes listed.

In contrast, the other options—Assist/control (A/C) mode, Synchronous intermittent mandatory ventilation (SIMV) mode, and Pressure support ventilation (PSV) mode—are all primary modes of mechanical ventilation. A/C provides mandatory breaths and assists patient-initiated breaths, SIMV allows for a combination of mandatory breaths and patient-initiated breaths with the flexibility of spontaneous breathing, and PSV supports each breath initiated by the patient with a preset pressure. Each of these modes actively contributes to ventilating the patient and managing their respiratory needs.