Vasopressin may be used in cardiac arrest when:

a. The patient has regained consciousness and needs blood pressure support
b. As an antiarrhythmic agent
c. As a replacement for the first or second epinephrine dose
d. To increase heart rate in symptomatic bradycardia

c
Rationale: c. Current guidelines suggest the use of vasopressin to replace the first or second dose of epinephrine in cardiac arrest.