Final answer:
The most important intervention for the nurse to implement is to maintain strict intake and output.
Step-by-step explanation:
The most important intervention for the nurse to implement in this case is to maintain strict intake and output. The patient is experiencing severe nausea and vomiting, which can lead to dehydration. Monitoring the intake and output of fluids is crucial to determine the level of hydration and to ensure that the patient receives appropriate fluid replacement.