Final answer:
In the case of a primigravida experiencing hypotension after an epidural, administering a vasopressor such as ephedrine or phenylephrine is a common treatment to increase her blood pressure.
Step-by-step explanation:
A primigravida dilated to 5 cm who has just received an epidural and complains of feeling lightheaded and dizzy with a significant drop in blood pressure is likely experiencing hypotension as a side effect of the epidural anesthesia. After administering a fluid bolus, one of the preferred medications to increase her blood pressure would be ephedrine or phenylephrine, which are both vasopressors commonly used to treat hypotension during epidurals. These medications work by constricting blood vessels, thereby increasing vascular resistance and restoring blood pressure levels.