Final answer:
The appropriate course of action for a patient with altered mental status, rapid, shallow respirations, and a thready pulse is to begin ventilatory assistance.
Step-by-step explanation:
In this scenario, the patient is experiencing an altered mental status along with rapid, shallow respirations and a thready pulse. These signs indicate a potentially life-threatening condition, such as cardiac or respiratory failure. Therefore, the appropriate course of action would be to begin ventilatory assistance, as the patient is not breathing adequately on their own.