Final answer:
The ventilatory support mode where the patient's work of breathing is least is continuous mandatory ventilation (CMV), as the ventilator performs all the work of breathing.
Step-by-step explanation:
The mode of ventilatory support in which the patient's work of breathing would be least is continuous mandatory ventilation (CMV). CMV provides full ventilatory support by delivering a set number of breaths of a set volume or pressure, depending upon the mode, to the patient regardless of the patient's own respiratory efforts. This reduces the patient's work of breathing significantly as the ventilator does all the work of breathing for them. In contrast, modes like continuous positive airway pressure (CPAP) and pressure-supported ventilation (PSV) assist with the effort, but still require the patient to initiate some or all of the breaths. Intermittent mandatory ventilation (IMV) allows spontaneous breathing in between mandatory breaths, which means there is still some work required from the patient.