Which forms of mechanical ventilation produce tidal volumes at or below the anatomic dead space?

High-frequency oscillation is the correct choice because it is specifically designed to deliver very small tidal volumes, which can be at or below the level of anatomic dead space. This form of mechanical ventilation operates by delivering rapid bursts of gas at a high frequency, allowing for effective gas exchange while minimizing the risk of lung injury due to over-distension or barotrauma. The small tidal volumes in high-frequency oscillation align closely with the respiratory physiology, making it useful in patients with conditions like Acute Respiratory Distress Syndrome (ARDS) where lung protection is essential.

In contrast, the other forms of ventilation mentioned generally utilize larger tidal volumes than what is considered safe for such patients. Inverse I:E ratio ventilation, for example, modifies the normal expiratory phase to increase lung recruitment but still uses traditional tidal volumes. Pressure support ventilation delivers a set tidal volume based on the patient's needs, often exceeding the dead space. Low-frequency positive-pressure ventilation similarly provides larger tidal volumes with longer inspiratory times that do not conform to the dead space constraint. These methods can contribute to over-distension in certain clinical situations, highlighting why high-frequency oscillation stands out for maintaining ventilation while minimizing potential harm.