Final answer:
Vasoactive medications for a client in shock should be administered via continuous infusion to allow for rapid and precise control of the medication's effects. Therefore, the correct option is c.
Step-by-step explanation:
When caring for a client in shock and administering vasoactive medications, the ICU nurse should use continuous infusion to provide a controlled and titratable effect. This method allows for immediate effect and precise dose management crucial in managing a patient's blood pressure and heart function. Other methods such as intramuscular injection, intermittent bolus injections, and oral medications are not appropriate in this situation due to the need for rapid and finely adjustable dosing that can only be achieved through continuous intravenous infusion.