Final answer:
The highest priority nursing action the nurse must perform before leaving the client's room is ensuring client safety. Acute diarrhea can lead to dehydration and electrolyte imbalances, which can be life-threatening.
Step-by-step explanation:
The highest priority nursing action the nurse must perform before leaving the client's room is ensuring client safety. Acute diarrhea can lead to dehydration and electrolyte imbalances, which can be life-threatening. The nurse should ensure that the client has access to fluids, is able to maintain good hygiene, and is in a safe environment to prevent falls or injury.
Documenting the vital signs and providing comfort measures are also important, but ensuring client safety takes precedence. Notifying the healthcare provider may be necessary, but it may not be the highest priority in this situation.