Which of the following is NOT a secondary mode of mechanical ventilation?

The correct answer is based on the understanding of the classification of mechanical ventilation modes. Secondary modes are typically those that are used in combination with primary modes to enhance patient ventilation while maintaining some degree of spontaneous breathing.

Open lung ventilation refers to a strategy rather than a specific ventilation mode. It focuses on keeping the alveoli open to improve oxygenation and lung mechanics and is not categorized strictly as a mode of ventilation. This strategy can often be applied across different primary modes of ventilation.

In contrast, inverse ratio ventilation (IRV), pressure regulated volume control (PRVC), and proportional assist ventilation (PAV, PAV+) are all recognized as ventilatory support modes that actually assist in achieving specific ventilation goals through established control mechanisms. They are designed specifically to interact with the patient's breathing pattern and support the ventilation process either by controlling pressure or volume while allowing for varying levels of spontaneous breathing.

Thus, since open lung ventilation does not fit the criteria of a specific mechanical ventilatory mode, it is categorized as the option that does not belong in the list of secondary modes.